About 1815 Pacific standard time on December 28, 1978, United Airlines, Inc., Flight
173 crashed into a wooded, populated area of suburban Portland, Oregon, during an approach
to the Portland International Airport. The aircraft had delayed southeast of the airport
at a low altitude for about 1 hour while the flightcrew coped with a landing gear
malfunction and prepared the passengers for a possible emergency landing. The plane
crashed about 6 nmi southeast of the airport. The aircraft was destroyed; there was no
fire. Of the 181 passengers and 8 crewmembers aboard, 8 passengers, the flight engineer,
and a flight attendant were killed and 21 passengers and 2 crewmembers were injured
The National Transportation Safety Board determined that the probable cause of the
accident was the failure of the captain to monitor properly the aircraft's fuel state and
to properly respond to the low fuel state and the crewmember's advisories regarding fuel
state. This resulted in fuel exhaustion to all engines. His inattention resulted from
preoccupation with a landing gear malfunction and preparations for a possible landing
Contributing to the accident was the failure of the other two flight crewmembers either
to fully comprehend the criticality of the fuel state or to successfully communicate their
concern to the captain.
1. FACTUAL INFORMATION
1.1 History of the Flight
On December 28, 1978, United Airlines, Inc., Flight 173, a McDonnell-Douglas DC-8-61
(N8082U), was a scheduled flight from John F. Kennedy International Airport, New York, to
Portland International Airport, Portland, Oregon, with an en route stop at Denver,
Flight 173 departed from Denver about 1447 1/ with 189
persons on board, including 6 infants, and 8 crewmembers. The flight was cleared to
Portland on an instrument flight rules (IFR) flight plan. The planned time en route was 2
hrs 26 min. The planned arrival time at Portland was 1713.
According to the automatic flight plan and monitoring systems 2/
the total amount of fuel required for the flight to Portland was 31,900 lbs. There was
46,700 lbs of fuel on board the aircraft when it departed the gate at Denver. This fuel
included the Federal Aviation Regulation requirement for fuel to destination plus 45 min
and the company contingency fuel of about 20 min. During a postaccident interview, the
captain stated that he was very close to his predicted fuel for the entire flight to
Portland "...or there would have been some discussion of it." The captain also
explained that his flight from Denver to Portland was normal.
At 1705:47, Flight 173 called Portland Approach and advised that its altitude was
10,000 ft 3/ and its airspeed was being reduced. Portland
responded and told the flight to maintain its heading for a visual approach to runway 28.
Flight 173 acknowledged the approach instructions and stated, "...we have the field
At 1707:55, Portland Approach instructed the flight to descend and maintain 8,000 ft.
Flight 173 acknowledged the instructions and advised that it was "leaving ten."
At 1709:40, Flight 173 received and acknowledged a clearance to continue its descent to
During a postaccident interview, the captain stated that, when Flight 173 was
descending through about 8,000 ft, the first officer, who was flying the aircraft,
requested the wing flaps be extended to 15, then asked that the landing gear be lowered.
The captain stated that he complied with both requests. However, he further stated that,
as the landing gear extended, "...it was noticeably unusual and (I) feel it seemed to
go down more rapidly. As (it is) my recollection, it was a thump, thump in sound and feel.
I don't recall getting the red and transient gear door light. The thump was much cut of
the ordinary for this airplane. It was noticeably different and we got the nose gear green
light but no other lights." The captain also said the first officer remarked that the
aircraft "yawed to the right
." Flight attendant and passenger statements
also indicate that there was a loud noise and a severe jolt when the landing gear was
At 1712:20, Portland Approach requested, "United one seven three heavy, contact
the tower (Portland), one one eight point seven." The flight responded,
"negative, we'll stay with you. We'll stay at five. We'll maintain about a hundred
and seventy knots. We got a gear problem. We'll let you know." This was the first
indication to anyone on the ground that Flight 173 had a problem. At 1712:28, Portland
Approach replied, "United one seventy -- three heavy roger, maintain five thousand.
Turn left heading two zero zero." The flight acknowledged the instructions.
At 1714:43, Portland Approach advised, "United one seventy three heavy, turn left
heading, one zero zero and I'll just orbit you out there 'til you get your problem."
Flight 173 acknowledged the instructions.
For the next 23 min, while Portland Approach was vectoring the aircraft in a holding
pattern south and east of the airport, the flightcrew discussed and accomplished all of
the emergency and precautionary actions available to them to assure themselves that all
landing gear was locked in the full down position. The second officer checked the visual
indicators on top of both wings, which extend above the wing surface when the landing gear
The captain stated that during this same time period, the first flight attendant came
forward and he discussed the situation with her. He told her that after they ran a few
more checks, he would let her know what he intended to do.
About 1738, Flight 173 contacted the United Airlines Systems Line Maintenance Control
Center in San Francisco, California, through Aeronautical Radio, Inc. 4/
According to recordings, at 1740:47 the captain explained to company dispatch and
maintenance personnel the landing gear problem and what the flightcrew had done to assure
that the landing gear was fully extended. He reported about 7,000 lbs of fuel on board and
stated his intention to hold for another 15 or 20 minutes. He stated that he was going to
have the flight attendants prepare the passengers for emergency evacuation.
At 1744:03, United San Francisco asked, "okay, United one seventy three....You
estimate that you'll make a landing about five minutes past the hour. Is that okay?"
The captain responded, "Ya, that's good ball park. I'm not gonna hurry the girls. We
got about a hundred sixty five people on board and we...want to...take our time and get
everybody ready and then we'll go. It's clear as a bell and no problem."
The aircraft continued to circle under the direction of Portland Approach in a
triangular pattern southeast of the airport at 5,000 ft. The pattern kept that aircraft
within about 20 nmi of the airport.
From about 1744:30 until about 1745:23, the cockpit voice recorder (CVR) contained
conversation between the captain and the first flight attendant concerning passenger
preparation, crash landing procedures, and evacuation procedures. During his initial
interview, the captain indicated that he neither designated a time limit to the flight
attendant, nor asked her how long it would take to prepare the cabin. He stated that he
assumed 10 or 15 minutes would be reasonable and that some preparations could be made on
the final approach to the airport.
At 1746:52, the first officer asked the flight engineer, "How much fuel we
got...?" The flight engineer responded, "Five thousand." The first officer
acknowledged the response.
At 1748:38, Portland Approach advised Flight 173 that there was another aircraft in its
vicinity. The first officer advised Portland Approach that he had the aircraft in sight.
At 1748:54, the first officer asked the captain, "...what's the fuel show
now...?" The captain replied, "Five." The first officer repeated,
"Five." At 1749, after a partially unintelligible comment by the flight engineer
concerning fuel pump lights, the captain stated, "That's about right, the feed pumps
are starting to blink." According to data received from the manufacturer, the total
usable fuel remaining when the inboard feed pump lights illuminate is 5,000 lbs. At this
time, according to flight data recorder (FDR) and air traffic control data, the aircraft
was about 13 nmi south of the airport on a west southwesterly heading.
From just after 1749 until 1749:45, the flightcrew engaged in further conversation
about the status of the landing gear. This conversation was interrupted by a heading
change from Portland Approach and was followed by a traffic advisory from Portland
About 1750:20, the captain asked the flight engineer to "Give us a current card on
weight. Figure about another fifteen minutes." The first officer responded,
"Fifteen minutes?" To which the captain replied, "Yeah, give us three or
four thousand pounds on top of zero fuel weight." The flight engineer then said,
"Not enough. Fifteen minutes is gonna -- really run us low on fuel here." At
1750:47, the flight engineer gave the following information for the landing data card:
"...Okay. Take three thousands pound, two hundred and four." At this time the
aircraft was about 18 nmi south of the airport in a turn to the northeast.
At 1751:35, the captain instructed the flight engineer to contact the company
representative at Portland and apprise him of the situation and tell him that Flight 173
would land with about 4,000 lbs of fuel. From 1752:17 until about 1753:30, the flight
engineer talked to Portland and discussed the aircraft's fuel state, the number of persons
on board the aircraft, and the emergency landing preparations at the airport. At 1753:30,
because of an inquiry from the company representative at Portland, the flight engineer
told the captain, "He wants to know if we'll be landing about five after." The
captain replied, "Yea." The flight engineer relayed the captain's reply to the
company representative. At this time the aircraft was about 17 nmi south of the airport
At 1755:04, the flight engineer reported the "...approach descent check is
complete." At 1756:53, the first officer asked, "How much fuel you got
now?" The flight engineer responded that 4,000 lbs remained, 1,000 lbs in each tank.
At 1757:21, the captain sent the flight engineer to the cabin to "...kinda see how
things are going...." From 1757:30 until 1800:50, the captain and the first officer
engaged in a conversation which included discussions of giving the flight attendants ample
time to prepare for the emergency, cockpit procedures in the event of an evacuation after
landing, whether the brakes would have antiskid protection after landing, and the
procedures the captain would be using during the approach and landing.
At 1801:12, Portland Approach requested that the flight turn left to a heading of 195
deg. The first officer acknowledged and compiled with the request.
At 1801:34, the flight engineer returned to the cockpit and reported that the cabin
would be ready in "another two or three minutes." The aircraft was about 5 nmi
southeast of the airport turning to a southwesterly heading. Until about 1802:10, the
captain and the flight engineer discussed the passengers and their attitudes toward the
At 1802:22, the flight engineer advised, "We got about three on the fuel and
that's it." The aircraft was then about 5 nmi south of the airport on a southwest
heading. The captain responded, "Okay. On touchdown, if the gear folds or something
really jumps the track, get those boost pumps off so that
you might even get the
At 1802:44, Portland Approach asked Flight 173 for a status report. The first officer
replied, "Yeah, we have indication our gear is abnormal. It'll be our intention, in
about five minutes, to land on two eight left. We would like the equipment standing by.
Our indications are the gear is down and locked. We've got our people prepared for an
evacuation in the event that should become necessary."
At 1803:14, Portland Approach asked that Flight 173 advise them when the approach would
begin. The captain responded, "...They've about finished in the cabin. I'd guess
about another three, four, five minutes." At this time the aircraft was about 8 nmi
south of the airport on a southwesterly heading.
At 1803:23, Portland Approach asked Flight 173 for the number of persons on board and
the amount of fuel remaining. The captain replied, "...about four thousand, well,
make it three thousand, pounds of fuel," and "you can add to that one
seventy-two plus six laps-infants."
From 1803:38 until 1806:10, the flightcrew engaged in a conversation which concerned
(1) checking the landing gear warning horn as further evidence that the landing gear was
fully down and locked and (2) whether automatic spoilers and antiskid would operate
normally with the landing gear circuit breakers out
At 1806:19, the first flight attendant entered the cockpit. The captain asked,
"How you doing?" She responded, "Well, I think we're ready." At this
time the aircraft was about 17 nmi south of the airport on a southwesterly heading. The
conversation between the first flight attendant and the captain continued until about
1806:40 when the captain said, "Okay. We're going to go in now. We should be landing
in about five minutes." Almost simultaneous with this comment, the first officer
said, "I think you just lost number four..." followed immediately by advice to
the flight engineer, "...better get some crossfeeds open there or something."
At 1806:46, the first officer told the captain, "We're going to lose an
engine...." The captain replied, "Why?" At 1806.49, the first officer again
stated, "We're losing an engine." Again the captain asked, "Why?" The
first officer responded, "Fuel."
Between 1806:52 and 1807:06, the CVR revealed conflicting and confusing conversation
between flight crewmembers as to the aircraft's fuel state. At 1807:06, the first officer
said, "It's flamed out"
At 1807:12, the captain called Portland Approach and requested, "...would like
clearance for an approach into two eight left, now." The aircraft was about 19 nmi
south southwest of the airport and turning left. This was the first request for an
approach clearance from Flight 173 since the landing gear problem began. Portland Approach
immediately gave the flight vectors for a visual approach to runway 28L. The flight turned
toward the vector heading of 010 deg.
From 1807:27 until 1809:16, the following intracockpit conversation took place:
1807:27 - Flight Engineer: "We're going to lose number three in a minute,
1807:31 - Flight Engineer: "It's showing zero."
Captain: "You got a thousand pounds. You got to."
Flight Engineer: "Five thousand in there...but we lost it."
1807:38 - Flight Engineer: "Are you getting it back?"
1807:40 - First Officer: "No number four. You got that crossfeed open?"
1807:41 - Flight Engineer: "No, I haven't got it open. Which one?
1807:42 - Captain: "Open em both -- get some fuel in there. Got some fuel
Flight Engineer: "Yes sir."
1807:48 - Captain: "Rotation. Now she's coming."
1807:52 - Captain: "Okay, watch one and two. We're showing down to zero or a
Flight Engineer: "Yeah."
Captain: "On number one?"
Flight Engineer: "Right."
1808:08 - First Officer: "Still not getting it."
1808:11 - Captain: "Well, open all four crossfeeds."
Flight Engineer: "All four?"
1808:14 - First Officer: "Alright, now it's coming."
18 08:19 - First Officer: "It's going to be -- on approach though."
Unknown Voice: "Yeah."
1808:42 - Captain: "You gotta keep 'em running...."
Flight Engineer: "Yes, sir."
1808:45 - First Officer: "Get this...on the ground."
Flight Engineer: "Yeah. It's showing not very much more fuel."
1809:16 - Flight Engineer: "We're down to one on the totalizer. Number two is
At 1809:21, the captain advised Portland Approach, "United seven three is going to
turn toward the airport and come on in." After confirming Flight 173's intentions,
Portland Approach cleared the flight for the visual approach to runway 28L.
At 1810:17, the captain requested that the flight engineer "reset that circuit
breaker momentarily. See if we get gear lights." The flight engineer complied with
At 1810:47, the captain requested the flight's distance from the airport. Portland
approach responded, "I'd call it eighteen flying miles." At 1812:42, the captain
made another request for distance. Portland Approach responded, "Twelve flying
miles." The flight was then cleared to contact Portland tower.
At 1813:21, the flight engineer stated, "We've lost two engines, guys." At
1813:25, he stated, "We just lost two engines - one and two."
At 1813:38, the captain said, "They're all going. We can't make Troutdale." 5/ The first officer said, "We can't make anything."
At 1813:46, the captain told the first officer, "Okay. Declare a mayday." At
1813:50, the first officer called Portland International Airport tower and declared,
"Portland tower, United one seventy three heavy, Mayday. We're -- the engines are
flaming out. We're going down. We're not going to be able to make the airport." This
was the last radio transmission from Flight 173.
About 1815, the aircraft crashed into a wooded section of a populated area of suburban
Portland about 6 nmi east southeast of the airport. There was no fire. The wreckage path
was about 1,554 ft long and about 130 ft wide.
The accident occurred during the hours of darkness at latitude 45031'21"N
and longitude 122029'59"W. The elevation of the accident site was 285 ft.
1.3 Damage to Aircraft
The aircraft was destroyed.
1.4 Other Damage
Two unoccupied homes were destroyed. Telephone lines were cut and high-tension
electrical powerlines were damaged.
1.5 Personnel Information
The crewmembers were properly certificated and qualified for the flight (See Appendix
1.6 Aircraft Information
The aircraft was certificated and maintained in accordance with Federal Aviation
Administration (FAA) requirements. The gross weight and center of gravity were within
prescribed limits for the approach and landing. There was no usable fuel in the aircraft
when it crashed.
The figures below illustrate the aircraft's approximate takeoff gross weight,
approximate landing weight, and the approximate pounds of fuel remaining upon arrival in
the vicinity of the Portland International Airport; these figures are based on normal
Zero fuel weight from weight
Total fuel on board from fuel
Aircraft weight before departure
from gate at Denver
Fuel consumption on taxi
Takeoff gross weight
Fuel consumption en route to
Portland, based on flight plan
Landing weight at Portland
Zero fuel weight from weight
Fuel remaining at Portland
Throughout the landing delay, Flight 173 remained at 5,000 ft with landing gear down
and flaps set at 15 deg. Under these conditions, the Safety Board estimated that the
flight would have been burning fuel at the rate of about 13,209 lbs per hour -- 220 lbs
per min. At the beginning of the landing delay, there were about 13,334 lbs of fuel on
A new type of fuel quantity indicating system was retrofitted to this aircraft on May
12, 1978. The retrofit was authorized by Change Order Authorization No. 2-4849. With the
new system installed, there are eight individual tank quantity gages. Each of these gages
has three digits which are seven-segment incandescent lamps. On these individual tank
gages, the digital reading is multiplied by 100 to obtain the total amount of fuel in the
The totalizer gage receives input from each individual tank gage and displays the total
fuel available on three digital readouts. However, this digital reading must be multiplied
by 1,000 to obtain the value of the total amount of fuel on board. The smallest increment
of change that can be indicated on the individual tank gages is 1,000 lbs. The smallest
increment of change on the totalizer is 1,000 lbs.
Before the implementation of the change order, each individual tank gage displayed five
digits which were read directly to obtain the amount of fuel in each tank.
The change order also replaced the flight engineer's totalizer gage, which had
displayed six digits read directly for total fuel on board.
According to United Airlines, the primary purposes of installing the fuel quantity
indicating system were (1) to reduce erroneous system indications because of stray pickup
of 400 Hz signals in the fuel quantity indicating system wiring, and (2) to reduce
indication errors from current leaks across the elements of the capacitive probes and
After the accident, United Airlines determined that the aircraft was burning fuel in
accordance with the automatic flight plan and monitoring system. In October 1978, fuel
burnoff examination indicated that the aircraft was not consuming fuel as fast as
predicted; it was 1.04 percent less than predicted. In addition, another method for
determining burnout was begun by United engineers. Each trip's total burnout was divided
by total time. For December 1978 these aggregate values verified that this aircraft's fuel
consumption was within 1 percent of the plan.
The aircraft was also equipped with a fuel flow indicator for each engine which
displayed, in hundreds of pounds, the hourly rate of fuel being used by the engine. These
indicators were located on the pilot's forward engine instrument panel along with other
engine monitoring gages.
1.7 Meteorological Information
Surface weather observations taken before and after the accident at Portland
International Airport by National Weather Service personnel were:
1655 - 4,500 ft scattered; visibility -- 30 mi; temperature -- 300F;
dewpoint -- 130F; wind -- 3400 at 8 kns; altimeter setting -- 30.16
1755 - Clear; visibility -- 15 mi; temperature -- 290F; dewpoint -- 13
F; wind -- 0100 at 11 kns; altimeter setting -- 30.17 in Hg.
1829 Local - Clear; visibility -- 15 mi; temperature -- 280F dewpoint --
120F; wind -- 3500 at 11 kns; altimeter setting -- 30.19 in Hg; AIRCRAFT
1.8 Aids to Navigation
During his deposition, the captain stated that he had set the Portland VORTAC, which is
located 9.2 nmi north-northeast of Portland International Airport, in both of his VOR
receivers. He stated also that he was receiving distance measuring equipment information.
No communications difficulties were reported.
1.10 Aerodrome Information
Runway 28L at Portland International Airport is hard surfaced and is 11,014 ft long and
150 ft wide. The published touchdown zone elevation and field elevation are 19 ft and 26
ft, respectively. The runway is equipped with high intensity runway edge lights,
centerline lights, and visual approach slope indicator lights. The airport has two other
runways. Runway 10L/28R, which is parallel to runway 28L, is 8,004 ft long and 150 ft
wide. It is the primary instrument runway. Runway 02/20 is 7,000 ft long and 150 ft wide.
It is used mainly as a crosswind runway.
The airport is located near the south shore of the Columbia River southeast of
Portland. The terrain southeast of the airport is characterized by low rolling hills,
which rise from the river valley.
1.11 Flight Recorders
N8082U was equipped with a Fairchild model 5424 flight data recorder (FDR), serial No.
6043. The recorder showed no outward evidence of damage. The foil recording medium was not
damaged; all parameter and binary traces were present and active with no evidence of
recorder malfunction or recording abnormalities. Electrical power to the recorder was
terminated about 44 sec before the aircraft crashed. A readout was made of the final 15
min 44.7 sec of the recorded traces. This readout covers the 15 min of flight before all
parameter traces -- altitude, airspeed, magnetic heading, and vertical acceleration --
ceased to be recorded and continues for an additional 44.7 sec where all binary traces
N8082U was also equipped with a Sundstrand model V557 CVR, serial No. 1427. The
recorder was removed from the aircraft and the entire tape was transcribed. The quality of
the recording was good. (See Appendix D.)
1.12 Wreckage and Impact Information
The aircraft first struck two trees about 100 ft above the ground. These trees were
about 1,554 ft from the point where the wreckage came to rest. About 541 ft farther along
the flightpath on a heading of about 345 deg, the aircraft struck two trees about 85 ft
above the ground. About 400 ft farther, the right wing struck a tree about 45 ft above the
ground. About 225 ft beyond that point, the left outer wing struck a tree about 8 ft above
the ground. The aircraft then struck and destroyed an unoccupied house which was located
about 1,230 ft from the first tree. Pieces of the aircraft's left wing structure were
located just beyond the house.
The two main landing gear and the nose section of the aircraft first struck a 5-ft
embankment next to a city street about 1,275 ft from the first tree. The aircraft
continued across the street and came to rest on a heading of 330 between some trees and on
top of another unoccupied house. The tail of the aircraft came to rest about 1,350 ft from
the first tree. Just after crossing the street, the vertical stabilizer struck a series of
high tension cables, which ran parallel to the street.
The fuselage, from about the fifth row of passenger seats forward, sustained severe,
extensive impact damage in a generally rearward direction. The cockpit upper structure,
which included the cockpit forward windows, had separated and was found to the right of
the fuselage just forward of the inboard end of the right wing. The cockpit floor
structure, which included portions of the crew seats, sections of the instrument panel,
and the nose tunnel structure with the nose gear assembly partially attached, had
separated and rotated to the right and aft. This structure was in a partially inverted
position. All portions of the fuselage structure were accounted for and all of the
structural damage was caused by impact with the ground and the numerous large trees in the
The lower left side of the fuselage, between the fourth and sixth rows of passenger
seats and below window level, had been torn away. The remainder of the underside of the
fuselage sustained heavy damage from contact with several large trees and tree stumps. The
passenger cabin interior, from row 6 to the aft bulkhead, was relatively intact. At
several points along the fuselage, windows were smashed and the fuselage had been dented
by large trees and separated portions of the main landing gear.
The empennage showed moderate impact damage. The vertical stabilizer leading edge had
been damaged by high tension cables at three points just forward of the upper three
rudder-to-stabilizer hinge points.
The left wing had separated from the fuselage about 3 ft outboard from the fuselage
attachment point. The No. 2 engine had separated from its pylon and was located adjacent
to the wing trailing edge. The No. 1 engine remained attached to a section of left wing
structure. A 7-ft-long section of the left wingtip had been sheared off and was found near
the first house.
The right wing separated about 5 ft from the fuselage. A 2-ft opening was evident
between the fuselage and wing leading edge structure. The wing leading edge, from a point
about 5 ft outboard from the leading edge inboard end, was cut and torn aft to the front
spar assembly. A large section of right wing leading edge structure had separated during
the impact sequence and was also found near the first house.
A section of right wing with the No. 3 engine and pylon attached was located just
forward of the right horizontal stabilizer. The outboard wing section, which included the
No. 4 engine, was to the right of the fuselage.
All four engines were inspected and found to be capable of operation. None showed signs
of rotation at impact
Both main landing gear were fully extended but were torn from their mounting
structures. They were located near main wreckage. Inspection of the right main landing
gear retraction mechanism showed corrosion in the threads of an attachment eyebolt. The
eyebolt was pulled out of the actuator cylinder piston. The nose landing gear was fully
extended and remained attached to the nose tunnel structure.
1.13 Medical and Pathological Information
A review of the flightcrew's medical records revealed no evidence of medical problems
that might have affected their performance.
The 10 persons who were killed in the crash died from impact trauma. Toxicological
analyses showed no acidic, neutral, or basic drugs or ethanol in the blood taken from the
flight engineer and first flight attendant
There was no fire.
1.15 Survival Aspects
The accident was partially survivable. The 10 occupants killed in the crash were
located between the flight engineer's station in the cockpit and row 5 in the passenger
cabin. All of the passengers who were killed had been located on the right side of the
cabin. That section of the aircraft was destroyed during the accident sequence.
The most seriously injured passengers were seated in the right forward portion of the
cabin near an area of the fuselage which appeared to have been penetrated by a large tree.
These persons were seated near those passengers who were injured fatally. Some seriously
injured passengers were seated in the rear cabin near the trailing edge of the wings. The
fuselage in this area had been penetrated and the floor and seats had been disrupted.
Some passengers sustained serious injuries during the evacuation. Two passengers
sustained fractures and others sustained lacerations and abrasions when they either fell
from exits or as they climbed through debris outside the aircraft in order to reach the
ground. As a result of the accident, 22 persons were admitted to hospitals with serious
injuries ranging from multiple fractures of extremities and fractures of cervical
vertebrae, to observations for possible injuries.
The plane crashed in the jurisdiction of Multnomah County Rural Fire Protection
District No. 10. Three fire departments sent personnel and equipment to the scene: The
Port of Portland (Airport) Fire Department; Multnomah RFPD No. 10, and the City of
Portland Fire Bureau. A total of 39 fire units and 108 on-duty fire personnel responded to
the scene. Numerous off-duty fire personnel from all fire departments also responded to
the scene. Because there was no fire, the basic fire service functions were search and
rescue, extrication, triage, emergency medical care, precautionary foaming of some
aircraft parts and surrounding area, laying standby firefighting water supply lines,
transporting or assisting ambulatory victims to a nearby church, setting up area lighting,
providing some interagency radio communications, and setting up the on-scene command post.
Although there were many occupied houses and apartment complexes in the immediate
vicinity of the accident, there were no ground casualties and no postcrash fire, injured
persons were transported to nearby hospitals by helicopter and ambulance.
The aircraft was equipped with 10 floor level exits, each provided with automatically
inflatable emergency escape slides. In addition to slides at the boarding doors (1L and
5L) and at the two galley service doors (2R and 5R), slides were located at the six
"jet escape" floor level exits (1R, 2L, 3L, 3R, 4L, 4R). The "jet
escape" doors were hinged at the bottom and were designed to swing down and outward
when opened. Movement of the door actuated the automatic inflation of the escape side.
The slide from exit 1L was found wrapped around a tree at the left wing. The slides
from exits 3L and 3R were found packed and uninflated. These exits were reportedly blocked
by debris outside the aircraft. The slide at exit 1R reportedly inflated inside the cabin
and extended across the aisle and lodged against seat 8C. The door was prevented from
opening fully because of cockpit and forward cabin debris outside the aircraft. The slide
at exit 2R also reportedly inflated inside the cabin and blocked the cabin aisle. The exit
door was displaced inward when the plane hit a tree.
The slide at exit 4R reportedly inflated inside the cabin when the door was opened by a
passenger. The slide inflated upward and partially blocked the exit opening. Because of
debris outside the fuselage, the exit door was prevented from opening fully. The passenger
who opened the door reported that about 10 persons used this exit before the slide was
pushed out the exit and onto debris. The remaining escape slides reportedly deployed
outside the aircraft and inflated but were punctured or torn by debris during the
The escape slides were removed from the accident site and were examined on January 3,
and on January 9, 1979. No discrepancies were found in the installation, maintenance,
manufacture, or design of the escape slides.
The evacuation was completed in about 2 min. Except for seats at rows 20 through 22
which were torn loose from the floor attachments, there was only minor disruption of the
cabin furnishings aft of row 6. The emergency lights provided adequate illumination during
1.16 Tests and Research
1.16.1 Retract Cylinder Assembly
The Safety Board examined the piston rod and the mating end from the right main landing
gear retract cylinder assembly at its metallurgical laboratory in Washington, D.C. The
examination showed that the primary cause of the separation of the rod end from the piston
rod was severe corrosion cause by moisture on to the mating threads of both components. As
a result of the corrosion, the joint was weakened to such an extent that only a
comparatively low tensile load was required to pull the rod end out of the piston rod. The
pattern of mechanical damage indicated that all of the rod threads had been engaged and
that the rod end had been pulled straight out of the piston rod without any significant
1.16.2 Fuel Control Test
Functional testing of the fuel controllers from each of the four engines was conducted
at the company's maintenance base. No discrepancies or out-of-tolerance conditions were
1.16.3 Aircraft Systems Examinations
During the week of January 8, 1979, the following examinations were conducted at the
company's maintenance facility:
(1) Fuel Flow indicators
The shop examinations confirmed that the four indicators were indicating zero fuel
flow. The front face, case, and electrical connections were all damaged and none could be
operated or tested before being repaired. After minor repairs to the electrical
connections only the flow meter for the No. 2 engine became operable, and it met the
(2) Fuel Quantity Gages
During the wreckage salvage, the eight fuel quantity gages were recovered. AU units
were damaged and repairs were attempted on each. Three gages could be repaired
sufficiently to allow functional testing.
The No. 4 main tank gage was given a lamp check, segment check, and self-test check and
all were within specification. In addition, a linearity check was made at full, at 1,000
lbs, at 500 lbs, and at empty. The results were within specifications. The No. 4 alternate
tank gage and the No. 2 main tank gage were tested in the same manner, and the results
were within specifications. The other tank gages were not operable because of damage and,
therefore, could not be tested.
(3) Totalizer Gage
The glass face was broken, the electrical connector bent, and the case punctured.
The damage was too extensive to enable repair for testing.
(4) No. 1 Main Fuel Tank Capacitance Probes
The five capacitance probes from the No. 1 main fuel tank were examined according
to company specification. All units were within specification except probe No. MR 28062,
serial No. 525856-31X. This unit did not meet resistance tolerance specification when wet.
(5) Tank Reference Capacitors
One of these units is located in each main tank. All four units were recovered and,
when tested, met specifications.
(6) Right Main Landing Gear Down-Lock Switch
This switch is activated when the gear reaches a down-and-locked position. A
similar switch was installed on the left main landing gear. A comparison of the damage to
the two switch cases showed that the switch from the right landing gear had been damaged
apparently by an internal part that pushed the case outward and had distorted it.
Electrical tests of the switch and attached wiring indicated an intermittent short circuit
when the switch was shaken. X-rays of the switch showed that a large spring had become
free of its mounts within the switch case. Normally this spring returns the down-lock
switch to the gear-not- down position when the landing gear is refracted. The switch case
was cut open and several coils of the spring were found spread apart. When the spring and
switch case damages were matched, one end of the spring fit into the distorted portion of
the case. The other end of the spring touched wiring terminal No. 8 of the microswitch and
marks indicative of electrical arcing were found on the spring where it contacted terminal
(7) Left Main Landing Gear Down-Lock Switch
The spring of the left main landing gear down lock switch was tree of its mounts.
The coils of this spring were not bent and no marks similar to electrical arcing were
(8) Landing Gear Warning and Interlock Circuit Breaker
When examined in the field, this circuit breaker appeared to be mechanically
extended or electrically open. There was some mechanical damage. Later, shop tests
verified that the circuit breaker was open. It could be operated mechanically and it
opened and closed the electrical circuit properly.
(9) Distance Measuring Equipment
Two distance measuring equipment units, Collins Model 860E-2, serial No. 3954 (No.
1) and serial No. 617 (No. 2), were opened in the company maintenance shops and the
distance modules were removed. When connected to a test panel, the mileage readouts were
16.05 nmi for the No. 1 unit and 16.0 nmi for the No.2 unit. Both units were selected to
channel 113X, which corresponds to a VOR frequency of 116.60 MHz.
1.16.4 Fuel Quantity System Error
Upon request, United Airlines provided the Safety Board with an error analysis of the
fuel quantity indicating system for the accident aircraft. Analyses were prepared for
three different assumptions. The first analysis assumed that all errors were at their
limits and in the same direction. The second analysis assumed that all errors were at
their limits but were distributed randomly with respect to sign (root-sum-square
analysis). The third analysis was a probable error analysis. All errors in this analysis
were those associated with empty or near empty tanks.
These analyses indicated the following:
High Error Lbs
Low Error Lbs
High Error Lbs
Low Error Lbs
1.16.5 Fuel Burn Time History
At the request of the Safety Board, Douglas Aircraft Company and United Airlines
studied fuel burn performance for the accident flight. In both studies, the fuel on board
at the gate in Denver was 46,700 lbs. The fuel remaining at cruise at 35,000 ft was almost
identical in both studies. United's calculations of fuel burn rate for the descent from
35,000 ft to the 5,000 -- ft holding altitude were 13 percent lower than Douglas'.
However, United's fuel burn rate while in the holding pattern was 14 percent higher than
Douglas'. This disparity was a result of different interpretations of meteorological and
FDR data which resulted in differing mach values. Both studies had similar fuel remaining
values when both flight recorders ceased operation; Douglas had calculated 178 lbs and
United had calculated 73 lbs. Both studies compared favorably to the fuel burn time
history computed by the Safety Board using information from the automatic flight plan and
monitoring system and CVR data.
A correlation of CVR information with both fuel burn studies shows the observed and
calculated fuel remaining values to be in agreement The CVR transcript indicated an
observed fuel remaining value of 5,000 lbs about 1749. The Douglas figure for that time
was 5,250 lbs and United's was about 6,000 lbs. If the totalizer accumulated probable
error of 885 lbs was applied, the calculated and observed fuel remaining values would be
in agreement. In addition, the two studies indicated that the accident aircraft's fuel
consumption was normal during the accident flight
Although both studies had similar fuel remaining values when the aircraft lost its
engine power, the Safety Board believes that the Douglas' study more closely approximates
the fuel burn during the 5,000-ft hold period. Therefore, fuel remaining computations for
this period are predicated on the manufacturer's figures of a calculated fuel burn of
13,209 lbs per hour (220 lbs per min). According to the manufacturer's study, the aircraft
entered into the hold with about 13,334 lbs of fuel.
1.17 Other Information
1.17.1 Responsibility of the Crew
Excerpt from United Airlines Flight Operations Manual, paragraph 6.2, June 30,
"16. Except as otherwise specifically directed by the captain, all crew
members noting a departure from prescribed procedures and safe practices should
immediately advise the captain so that he is aware of and understands the particular
situation and may take appropriate action."
1.17.2 United Airlines Flight Operations Bulletin 22-76, Fuel Policy Domestic
FAR 45 Minute and Overwater/International 30 Minute Reserve Fuel.
"FAR 121.639 (C) does not specify in detail how the aforementioned requirements
are to be calculated. United Airlines has established the following criteria for computing
a. Weight - The operating weight empty of the airplane plus maximum structural
payload or maximum space payload, whichever is smaller, plus the weight of the 45 minutes
of reserve fuel.
b. Speed - Long range cruise speed.
c. Altitude -- 25,000 Feet
d. The ability to loiter at 5,000 feet at clean holding speed for 45 minutes."
"From the aforementioned criteria is derived the following DC-8-61 fuel
1. Fuel required for 45 minutes cruising at long range cruise at 25,000 feet is 8,300
2. Fuel required for 45 minutes holding clean at 5,000 feet is 7,800 pounds.
3. FAR 45 minute reserve: 8,400 pounds."
1.17.3 Excerpts From United Airlines DC-8 Flight Manual
"Landing Gear Lever Down and Gear Unsafe Light On
If the visual down-lock indicators indicate the gear is down then a landing can be made
at the captain's discretion."
(Dated January 1, 1974, pg. 1-44.)
"Landing Gear Apparently But Not Conclusively Down
If possible, have tower visually check. If there is reasonable indication that the gear
is down then the landing can be made assuming gear is down. Do not taxi the airplane until
gear locks have been installed."
(Dated January 2, 1974, pg 1 -- 44-59.)
"Preparation For Evacuation
1. Notify ground station of emergency.
2. Advise the First Flight Attendant as to:
a. nature of emergency and expected landing conditions,
b. time available for preparation,
c. signal for taking protective position,
d. signal to be used if evacuation is not necessary,
e. other special instructions.
3. Determine from the First Flight Attendant:
a. the passenger load,
b. number of infants, invalids, and other passengers who would be given special
4. Direct all nonessential cockpit members to move to the cabin and assist Flight
Attendants as requested.
5. Review the EVACUATION Emergency procedure.
6. Make an announcement to the passengers as appropriate.
7. Accomplish the CABIN INSPECTION CHECKLIST below when advised by the First Flight
Attendant that cabin preparations are completed.
8. Depressurize the airplane when below 10,000 feet.
9. Insure that -- the emergency exit lights switch is in the armed position.
10. Avoid landing, if possible, until emergency equipment and crews are standing by.
11. Advise the First Flight Attendant when approximately five minutes from landing.
12. Advise the passengers and Flight Attendants when to assume the protective position.
13. If evacuation is necessary, accomplish the EVACUATION Emergency Procedure."
(Dated September 27, 1975, page 1 -- 19.)
"Cabin Inspection Checklist
1. All Flight Attendants briefed on station, duties, and signals.
2. Passengers reseated as required and seats to be used by crew vacated.
3. Helper passengers briefed on station, duties, and exit operation.
4. Passengers briefed on:
a. Protective position and signal to assume position.
b. Seatbelts tight and low.
c. How to unfasten seat belts.
d. Assigned exits and when and how to leave the airplane.
5. Passengers' glasses, dentures, high heels, and other possible hazardous items
removed and stowed. Loose objects stowed in secure stowage areas.
6. Internal doors and curtains secured open.
7. Meal service furnishings in appropriate secure area.
8. Seat backs upright and tables stowed. Pillows and blankets distributed for impact
(Dated September 27, 1975, page 1-20)
1.17.4 Excerpts From United Airlines Maintenance/Overhaul Manual
"Fuel Quantity Indicator System - Tolerance
a. All tanks at empty, +/- 150 pounds.
b. Tank at full #1 & #4 Main +/- 400 pounds
#1 & #4 Alt +/- 225 pounds
#2 & #3 Main +/- 400 pounds
#2 & #3 Alt +/- 250 pounds"
(Dated January 19, 1976, page 201.)
1.17.5 Main Landing Gear Retract Cylinder Assembly
Although the purpose of the main landing gear retract cylinder assembly is to raise the
landing gear during the refract cycle, the hydraulic action of the cylinder acts as a
buffer during the extend cycle to moderate the rate of extension and prohibit the landing
gear from free falling to the down-and-locked position.
McDonnell-Douglas Corporation issued an All-Operator Letter, AOL 8-141, in July 1967,
Main Landing Gear Retract Cylinder Assemblies, DC-8 Aircraft. The letter advised, all DC-8
operators that several cylinder end fittings had been found with fractures in the thread
roots. To alleviate this condition, the eyebolt threads were changed from machined to
rolled-type threads. The letter also recommended sealing the threads with a corrosion
On March 27, 1968, McDonnell-Douglas issued Service Bulletin No. 32-131, DC-8 SC 1681,
Landing Gear Extension and Retraction -Replace Main Landing Gear Retract Rod Assemblies.
This bulletin provided information on the replacement of the retract cylinder rod end
assemblies with machined threads with rod end assemblies with rolled-type threads.
In 1973, United Airlines instituted a gamma ray inspection program for the main landing
gear retract actuating cylinder and rod ends on the DC-8 aircraft. The purpose of
inspection was to detect thread corrosion in the cylinder. The cylinder threads on the
main landing gear refract actuators of the accident aircraft were last inspected using the
gamma ray injection on April 2, 1977.
In order to provide additional threads and a longer eyebolt on actuator cylinders found
with corrosion damage, the retract cylinder was to have been modified as provided for in
the United Airlines Maintenance Manual dated January 2, 1974. The right main landing gear
retract actuator on the accident aircraft had not been modified.
1.17.6 Dispatcher Responsibility and Authority
Under the provisions of United Airlines Flight Operations Manual, the flight dispatcher
responsibility after the aircraft is airborne is limited to computation of fuel estimate
under only two conditions -- when contact is not established within 20 min and during a
1.18 New Investigation Techniques
The flightcrew was properly certificated and each crewmember had received the training
and the off-duty time prescribed by applicable regulations. There was no evidence of
medical problems that might have affected their performance.
The aircraft was certificated and maintained according to applicable regulations. The
gross weight and c.g. were within prescribed limits. Except for the failure of the piston
rod on the right main landing gear retract cylinder assembly and the failure of the
landing gear position indicating system, the aircraft's airframe, system; structures, and
powerplants were not factors in this accident.
The investigation revealed that fuel was burned at a normal rate between Denver and
Portland. The aircraft arrived in the Portland area with the preplanned 13,800 lbs of fuel
and began its delay at 5,000 ft with about 13,334 lbs.
The first problem which faced the captain of Flight 173 was the unsafe landing gear
indication during the initial approach to Portland International Airport. This unsafe
indication followed a loud thump, an abnormal vibration, and an abnormal aircraft yaw as
the landing gear was lowered. The Safety Board's investigation revealed that the landing
gear problem was caused by severe corrosion in the mating threads where the right main
landing gear refract cylinder assembly actuator piston rod was connected to the rod end.
The corrosion allowed the two parts to pull apart and the right main landing gear to fall
free when the flightcrew lowered the landing gear. This rapid fall disabled the
microswitch for the right main landing gear which completes an electrical circuit to the
gear-position indicators in the cockpit. The difference between the time it took for the
right main landing gear to free fall and the time it took for the the left main landing
gear to extend normally, probably created a difference in aerodynamic drag for a short
time. This difference in drag produced a transient yaw as the landing gear dropped.
Although the landing gear malfunction precipitated a series of events which culminated
in the accident, the established company procedures for dealing with landing gear system
failure(s) on the DC-8-61 are adequate to permit the safest possible operation and landing
of the aircraft. Training procedure; including ground school, flight training, and
proficiency and recurrent training, direct the flightcrew to the Irregular Procedures
section of the DC-8 Flight Manual, which must be in the possession of crewmembers while in
flight. The Irregular Procedures section instructed the crew to determine the position of
both the main and nose landing gear visual indicators. "If the visual indicators
indicate the gear is down, then a landing can be made at the captain's discretion."
The flight engineer's check of the visual indicators for both main landing gear showed
that they were down and locked. A visual check of the nose landing gear could not be made
because the light which would have illuminated that down-and-locked visual indicator was
not operating. However, unlike the main landing gear cockpit indicators, the cockpit
indicator for the nose gear gave the proper "green gear-down" indication.
Admittedly, the abnormal gear extension was cause for concern and a flightcrew should
assess the situation before communicating with the dispatch or maintenance personnel.
However, aside from the crew's discussing the problem and adhering to the DC-8 Flight
Manual, the only remaining step was to contact company dispatch and line maintenance. From
the time the captain informed Portland Approach of the gear problem until contact with
company dispatch and line maintenance, about 28 min had elapsed. The irregular gear check
procedures contained in their manual were brief, the weather was good, the area was void
of heavy traffic, and there were no additional problems experienced by the flight that
would have delayed the captain's communicating with the company. The company maintenance
staff verified that everything possible had been done to assure the integrity of the
landing gear. Therefore, upon termination of communications with company dispatch and
maintenance personnel, which was about 30 min before the crash, the captain could have
made a landing attempt. The Safety Board believes that Flight 173 could have landed safely
within 30 to 40 min after the landing gear malfunction.
Upon completing communications with company, line maintenance and dispatch, the captain
called the first flight attendant to the cockpit to instruct her to prepare the cabin for
a possible abnormal landing. During the ensuing discussion, the captain did not assign the
first flight attendant a specified time within which to prepare the cabin, as required by
the flight manual. In the absence of such time constraint, the first flight attendant was
probably left with the impression that time efficiency was not necessarily as important as
the assurance of thorough preparation.
The Safety Board believes that any time a flight deviates from a flight plan, the
flightcrew should evaluate the potential effect of such deviation on the aircraft fuel
status. This flightcrew knew that the evaluation of the landing gear problem and
preparation for an emergency landing would require extended holding before landing.
The flightcrew should have been aware that there were 46,700 lbs of fuel aboard the
aircraft when it left Denver at 1433 and that there was about 45,650 lbs at takeoff at
1447. Regardless of whether they were aware of the actual fuel quantities, they certainly
should have been aware that the initial fuel load was predicated on fuel consumption for
the planned 2 hr 26 min en route flight, plus a reserve which includes sufficient fuel for
45 min at normal cruise and a contingency margin of about 20 min additional flight.
Therefore, the crew should have known and should have been concerned that fuel could
become critical after holding. Proper crew management includes constant awareness of fuel
remaining as it relates to time. In fact, the Safety Board believes that proper planning
would provide for enough fuel on landing for a go-around should it become necessary. Such
planning should also consider possible fuel-quantity indication inaccuracies. This would
necessitate establishing a deadline time for initiating the approach and constant
monitoring of time, as well as the aircraft's position relative to the active runway. Such
procedures should be routine for all flightcrews. However, based on available evidence,
this flightcrew did not adhere to such procedures. On the contrary, the cockpit
conversation indicates insufficient attention and a lack of awareness on the part of the
captain about the aircraft's fuel state after entering and even after a prolonged period
of holding. The other two flight crewmembers, although they made several comments
regarding the aircraft's fuel state, did not express direct concern regarding the amount
of time remaining to total fuel exhaustion. While there is evidence to indicate that the
crew was aware of the amount of fuel remaining at various times, there is no evidence that
the onboard quantity was monitored in relation to time remaining during the final 30 min
of flight. The Safety Board believes that had the flightcrew been aware of the fuel state,
comments concerning time to fuel exhaustion would have been voiced. However, there was
none until after the aircraft was already in a position from which recovery was not
In analyzing the flightcrew's actions, the Safety Board considered that the crew could
have been misled by inaccuracies within the fuel-quantity measuring system. However, those
intracockpit comments and radio transmissions in which fuel quantity was mentioned
indicate that the fuel-quantity indicating system was accurate.
Had the flightcrew related any of these fuel quantities to fuel flow, they should have
been aware that fuel exhaustion would occur at or about 1815. Other evidence that the
captain had failed to assess the effect of continued holding on fuel state was provided by
his stated intentions to land about 1805 with.4,000 lbs of fuel on board. Just minutes
earlier, at 1748:56, he was made aware that only 5,000 lbs remained. During the 16 min
between the observation of 5,000 lbs and 1805, the aircraft would consume at least 3,000
lbs of fuel. Further evidence of the flightcrew's lack of concern or awareness was
provided when just after his observations of 4,000 lbs remaining about 17 min before the
crash, the first officer left the cockpit at the captain's request to check on the cabin
emergency evacuation preparations. Upon his return, about 4 min later, he gave the captain
an estimate of another 2 or 3 min for the completion of the cabin preparation. At this
time, the aircraft was in the general vicinity of the airport. In the initial interview
with the captain, he stated that he felt the cabin preparation could be completed in from
10 to 15 min and that the "tail end of it" could be accomplished on the final
approach to the airport. Certainly there was nothing more to do in the cockpit. All of the
landing gear check procedures, as prescribed in the approved flight manual and recommended
by company line maintenance, had been completed and dispatch had been notified and had
alerted Portland company personnel of the problems.
Under these circumstances, there appears to have been no valid reason not to
discontinue their heading inbound toward the airport in order to make their previously
estimated landing time. However, about 1801:12, the first officer accepted and the captain
did not question a vector heading which would take them away from the airport and delay
their landing time appreciably. Moreover, after the turn was completed none of the
flightcrew suggested turning toward the airport. Thus, it was at this time that the crew's
continuing preoccupation with the landing gear problem and landing preparations became
crucial and an accident became inevitable.
The Safety Board also considered the possibility that the captain was aware of the fuel
quantity on board, but failed to relate the fuel state to time and distance from the
airport and intentionally extended the flight to reduce the fuel load in order to reduce
the potential of fire should the landing gear fail upon landing. The Safety Board could
find no evidence, however, to support such a theory and believes that had he so intended,
the captain would have advised the first officer and the flight engineer. Therefore, the
Safety Board can only conclude that the flightcrew failed to relate the fuel remaining and
the rate of fuel flow to the time and distance from the airport, because their attention
was directed almost entirely toward diagnosing the landing gear problem. Although on two
occasions the captain confirmed with the company that he intended to land about 1805 and
that he would be landing with about 4,000 lbs of fuel, this estimated time of arrival and
landing fuel load were not adhered to, nor was the expected approach time given to
Portland Approach. This failure to adhere to the estimated time of arrival and landing
fuel loads strengthens the Board's belief that the landing gear problem had a seemingly
disorganizing effect on the flightcrew's performance. Evidence indicates that their scan
of the instruments probably narrowed as their thinking fixed on the gear. After the No. 4
engine had flamed out and with the fuel totalizer indicating 1,000 lbs, the captain was
still involved in resetting circuit breakers to recheck landing gear light indications.
It was not until after it became apparent to the crew that total engine flame out was
imminent that the captain was concerned and, in fact, may have been confused as to the
amount of fuel which actually remained. About 6 min before all engines stopped, the
captain stated that there was 1,000 lbs of fuel in the No. 1 main tank, and the flight
engineer agreed with him. At this same time, the captain began to describe the gage
indication as changing from 1,000 lbs to zero lbs. Since the No. 1 main tank gage does not
change its indication from 1,000 lbs to zero lbs directly, but decreases in increments of
100 lbs, the captain must have read the gage indication incorrectly. Actually, the action
he described was that of a gage changing from 100 lbs to zero lbs.
The company had recently changed the fuel quantity gages on this aircraft from a direct
reading digital-type to a three-figure indicator that had to be multiplied by a factor of
100 to get the actual individual tank values. In addition, the new totalizer gage, of the
same three-figure presentation as the individual tank gages, had to be multiplied by a
factor of 1,000 to get the actual total fuel. During the stressed situation, the captain
and the flight engineer may have mixed up these multipliers and used 1,000 when reading
the individual tank gages instead of 100. However, there is no evidence from previous
comments that such a mistake was made. By the time such confusion was indicated, the
accident was inevitable.
The Safety Board believes that this accident exemplifies a recurring problem -- a
breakdown in cockpit management and teamwork during a situation involving malfunctions of
aircraft systems in flight. To combat this problem, responsibilities must be divided among
members of the flightcrew while a malfunction is being resolved. In this case, apparently
no one was specifically delegated the responsibility of monitoring fuel state.
Although the captain is in command and responsible for the performance of his crew, the
actions or inactions of the other two flight crewmembers must be analyzed.
Admittedly, the stature of a captain and his management style may exert subtle pressure
on his crew to conform to his way of thinking. It may hinder interaction and adequate
monitoring and force another crewmember to yield his right to express an opinion.
The first officer's main responsibility is to monitor the captain. In particular, he
provides feedback for the captain. If the captain infers from the first officer's actions
or inactions that his judgement is correct, the captain could receive reinforcement for an
error or poor judgement. Although the first officer did, in fact, make several subtle
comments questioning or discussing the aircraft's fuel state, it was not until after the
No. 4 engine flamed out that he expressed a direct view, "Get this...on the
ground." Before that time, the comments were not given in a positive or direct tone.
If the first officer recognized the criticality of the situation, he failed to convey
these thoughts to the captain in a timely manner.
The flight engineer's responsibility, aside from management of the aircraft systems, is
to monitor the captain's and first officer's actions as they pertain to the performance of
the aircraft, that is, takeoff, landing, holding speeds, and range of the aircraft
considering time and fuel flow. Although he informed the captain at 1750:30 that an
additional "fifteen minutes is really gonna run us low on fuel here," there is
no indication that he took affirmative action to insure that the captain was fully aware
of the time to fuel exhaustion. Neither is there an indication that, upon returning to the
cockpit at 1801:39, he relayed any concern about the aircraft's fuel state to the captain.
Although he commented that 3,000 lbs of fuel remained, he failed to indicate time
remaining or his views regarding the need to expedite the landing.
The first officer's and the flight engineer's inputs on the flight deck are important
because they provide redundancy. The Safety Board believes that, in training of all
airline cockpit and cabin crewmember, assertiveness training should be a part of the
standard curricula, including the need for individual initiative and effective expression
In order to determine whether the captain had received all available assistance during
the emergency, the Safety Board evaluated the actions of the company dispatcher and his
role relative to the accident sequence. According to the tape of the conversation between
the captain, the company dispatcher, and company line maintenance personnel, the captain
had advised the dispatcher that he had 7,000 lbs of fuel aboard and that he intended to
land in 15 or 20 min. The dispatcher then checked with the captain to ascertain a specific
time for the landing and the captain agreed that 1805 was "a good ballpark." The
dispatcher, according to his interview after the accident, then relayed this landing time
and the aircraft's status to the company personnel in Portland. He also stated that his
assessment of the situation was that of the fuel remaining upon landing would be low but
the landing could be made successfully at 1805. The Safety Board believes that, with the
information given to him by the captain, the dispatcher acted properly and in accordance
with company procedures.
In a number of airline accidents investigated by the Safety Board
in the 1960s and 1970s, the Board detected a culture and work environment in the cockpit
that, rather than facilitating safe transportation, may have contributed to the accidents.
The Board found that some captains treated their fellow cockpit crewmembers as underlings
who should speak only when spoken to. This intimidating atmosphere actually led to
accidents when critical information was not communicated among cockpit crewmembers. A
highly publicized accident in 1978 provided the impetus to change this situation.
On December 28, 1978, as a result of a relatively minor landing
gear problem, a United Airlines DC-8 was in a holding pattern while awaiting landing at
Portland, Oregon. Although the first officer knew the aircraft was low on fuel, he failed
to express his concerns convincingly to the captain. The plane ran out of fuel and
crashed, killing 10.
As a result of this accident and others, the concept of cockpit
resource management, now called crew resource management (CRM), was born. Following
pioneering work by the National Aeronautics and Space Administration (NASA), the Safety
Board issued recommendations to the FAA and the airline industry to adopt methods that
encourage teamwork, with the captain as the leader who relies on the other crewmembers for
vital safety-of-flight tasks and also shares duties and solicits information and help from
other crewmembers. United Airlines was one of the first airlines to adopt this concept,
which is endorsed by pilot unions and is now almost universally used by the major airlines
(as well as in other modes of transportation). The Board has also recommended and the FAA
has acted to implement CRM for regional and commuter airlines.
The value of CRM was demonstrated on July 19, 1989, when a United
Airlines DC-10 experienced a catastrophic engine failure over Iowa that destroyed the
aircrafts hydraulic systems, rendering it virtually uncontrollable. The cockpit crew
and a deadheading captain who was a passenger worked as a team to bring the aircraft down
to a crash landing at Sioux City. Although more than 100 people perished, almost 200
survived a situation for which no pilots in the world had ever been trained.
1. The flightcrew was properly certificated and qualified for the flight.
2. The aircraft was certificated, maintained, and dispatched in accordance with Federal
Aviation Regulations and approved company procedures.
3. Except for the failure of the piston rod on the right main landing gear retract
cylinder assembly, with the resulting damage to the landing gear position indicating
system switch, there was no evidence of a failure or malfunction of the aircraft's
structure, powerplants, flight controls, or systems.
4. The aircraft departed Denver with the required fuel aboard of 2 hrs 28 min for the
en route flight and with the required FAR and company contingency fuel aboard of about 1
5. The aircraft began holding about 1712 at 5,000 ft with its gear down; this was about
2 hrs 24 min after it departed Denver.
6. The landing delay covered a period of about 1 hr 2 min.
7. All of the aircraft's engines flamed out because of fuel exhaustion about 1815 -- 1
hr 3 min after it entered into hold and 3 hrs 27 min after it departed Denver.
8. Fuel exhaustion was predictable. The crew failed to equate the fuel remaining with
time and distance from the airport.
9. No pertinent malfunctions were found during examinations of the fuel-quantity
10. A new digital fuel-quantity indicating system was installed on this aircraft on May
12, 1978. This was in accordance with a DC-8 UAL fleetwide retrofit program.
11. Evidence indicates that the fuel quantity indicating system accurately indicated
fuel quantity to the crew.
12. The fuel gages are readily visible to the captain and the second officer.
13. The captain failed to make decisive timely decisions.
14. The captain failed to relate time, distance from the airport, and the aircraft's
fuel state as his attention was directed completely toward the diagnosis of the gear
problem and preparation of the passengers for an emergency landing. The gear problem had a
disorganizing effect on the captain's performance.
15. Neither the first officer nor the flight engineer conveyed any concern about fuel
exhaustion to the captain until the accident was inevitable.
3.2 Probable Cause
The National Transportation Safety Board determined that the probable cause of the
accident was the failure of the captain to monitor properly the aircraft's fuel state and
to properly respond to the low fuel state and the crewmember's advisories regarding fuel
state. This resulted in fuel exhaustion to all engines. His inattention resulted from
preoccupation with a landing gear malfunction and preparations for a possible landing
Contributing to the accident was the failure of the other two flight crewmembers either
to fully comprehend the criticality of the fuel state or to successfully communicate their
concern to the captain.
4. SAFETY RECOMMENDATIONS
As a result of this accident, the Safety Board has issued the following recommendations
to the Federal Aviation Administration:
"Issue an Operations Alert Bulletin to have FAA inspectors assure that crew
training stresses differences in fuel-quantity measuring instruments and that crews flying
with the new system are made aware of the possibility of misinterpretation of gage
readings. (Class II--Priority Action) (A-79-32)"
"Emphasize to engineering personnel who approve aircraft engineering changes or
issuance of Supplemental Type Certificates the need to consider cockpit configuration and
instrumentation factors which can contribute to pilot confusion, such as the use of
similar-appearing instruments with different scale factors. (Class II--Priority Action)
"Audit Supplemental Type Certificate SA3357WE-D for completeness, especially in
the area of system calibration after installation. (Class II--Priority Action)
"Issue an operations bulletin to all air carrier operations inspectors directing
them to urge their assigned operators to ensure that their flightcrews are indoctrinated
in principles of flightdeck resource management, with particular emphasis on the merits of
participative management for captains and assertiveness training for other cockpit
crewmembers. (Class II, Priority Action) (A-79-47)"
BY THE NATIONAL TRANSPORTATION SAFETY BOARD
/s/ JAMES B. KING
/s/ ELWOOD T. DRIVER
/s/ FRANCIS H. MCADAMS
/s/ PHILIP A. HOGUE
Investigation and Hearing
The Safety Board was notified of the accident about 2130 e.s.t. on December 28, 1978.
The investigation team went immediately to the scene. Working groups were established for
operations, air traffic control, witnesses, human factors, powerplants, structures,
system; maintenance records, weather, cockpit voice recorder, flight data recorder, and
Participants in the on-scene investigation included representatives of the Federal
Aviation Administration, United Airlines, Inc., Douglas Aircraft Company, Air Line Pilots
Association, Professional Air Traffic Controllers Association, Association of Flight
Attendants, International Association of Machinists, Multnomah County Sheriff's Office,
and Port of Portland.
2. Public Hearing
There was no public hearing held in conjunction with this accident investigation.
The captain was deposed at the Federal Aviation Administration's Rocky Mountain
Regional Headquarters in Denver, Colorado, on March 6,1979. Parties to the deposition
included representatives of the Federal Aviation Administration, United Airlines, Inc.,
Douglas Aircraft Company, and the Air Line Pilots Association.
1/ All times herein are Pacific standard, based on the 24-hour clock.
2/ A computer printout which predicted the amount of fuel that would be
used between several identifiable en route points. The flightcrew was able to check the
actual fuel used against the predicted fuel use at each of these points.
3/ All altitudes are mean sea level unless otherwise indicated.
4/ Aeronautical Radio, Inc., an air-to-ground radio service which
provides a communication system for commercial aircraft.
5/ A small airport on the final approach path to runway 28L.