Air Safety – Portland DC-8 accident

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.

Factual Information

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, Ore, with an en route stop at Denver, Colo.

Flight 173 departed from Denver about 1447 (All times herein are Pacific Standard, based on the 24-hour clock) with 189 persons on board, including six infants and eight crewmembers. The flight was cleared to Portland on an instrument flight rules (IFR) flight plan. The planned time en route was 2 hours 26 min. The planned arrival time at Portland was 1713.

According to the automatic flight plan and monitoring system (A computer printout which predicted the amount of fuel that would be used between several identifiable en route points. The flight crew was able to check the actual fuel used against the predicted fuel used at each of the points), the total amount of fuel required for the flight to Portland was 31,900Ib. There was 46,700Ib 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 10,000ft. (All altitudes are mean sea level unless otherwise indicated) 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 in sight”.

At 1707:55, Portland Approach instructed the flight to descend and maintain 8000ft. 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 6000ft.

During a postaccident interview, the captain stated that. when Flight 173 was descending through about 8000ft. the first officer. who was flying the aircraft, requested the wing flaps be extended to 15 deg. 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 out of the ordinary for this aeroplane. 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 lowered.

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 170 knots. We have 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 173 heavy roger. maintain 5000. Turn left heading two zero zero. ” The flight acknowledged the instructions.

At 1714:43, Portland Approach advised, “United one seven three heavy, turn left heading, one zero and I’ll just orbit you out there ’till 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 flight crew 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 extended above the wing surface when the landing gear was down and locked.

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.

At about 1738, Flight 173 contacted the United Airlines Systems Line Maintenance Control Center in San Francisco, California, through Aeronautical Radio. Inc (Aeronautical Radio, Inc. an air-to-ground radio service that provides a communication system for commercial aircraft. ) According to recordings, at 1740:47 the captain explained to company dispatch and maintenance personnel the landing gear problem and what the flight crew had done to ensure that the landing gear was fully extended. He reported about 7000Ib of fuel on board and stated his intention to hold for another 15 or 20 min. 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 seven-three . . . You estimate that you’ll make a landing about 5 min past the hour. Is that okay?” The captain responded, “Ya, that’s a good ballpark. I’m not gonna hurry the girls. We have about 165 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 5000ft. The pattern kept that aircraft within about 20 nautmi of the airport.

From about 1744:30 until about 1745:23. the cockpit voice recorder (CVR) contained a 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 min 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 5000Ib. At this time. according to flight data recorder (FDR) and air traffic control data, the aircraft was about 13 naut mi south of the airport on a west southwesterly heading.

From just after 1749 until 1749:45, the flight crew engaged in further conversation about the status of the landing gear. This conversation was interrupted by a heading change from the Portland Approach and was followed by a traffic advisory from the Portland Approach.

At about 1750:20, the captain asked the flight engineer to “Give us a current card on weight: figure about another 15 min. ” 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 thousand pounds, two hundred and four. ” At this time the aircraft was about 18 naut mi 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 4000Ib 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. “Yes. ” The flight engineer relayed the captain’s reply to the company representative. At this time the aircraft was about 17 naut mi south of the airport heading northeast.

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 4000Ib remained. 1000lb 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 that 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 complied with the request.

At 1801:34. the flight engineer returned to the cockpit and reported that the cabin would be ready in “another 2 or 3 min. ” The aircraft was about five naut mi 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 emergency.

At 1802. 22. the flight engineer advised. “We got about three on the fuel and that’s it. ” The aircraft was then about five naut mi 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 valves open. ”

At 1802:44, Portland Approach asked Flight 173 for a status report. The first officer replied. “Yeah. we have an indication our gear is abnormal. It’ll be our intention in about 5 min 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 3. 4, 5 min. . . At this time the aircraft was about eight naut mi 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 flight crew engaged in a conversation that 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 until the landing gear circuit breaks out.

At 1806:19. the first flight attendant entered the cockpit. The captain asked. “How are you doing?” She responded, “Well, I think we’re ready. ” At this time the aircraft was about 17 naut mi 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 5 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 CBR revealed conflicting and confusing conversations between flight crewmembers as the the 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 naut mi 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 01O 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. too . ”

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. ” Captain: “Alright. ”

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 pressure?” 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 thousand . . 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?” Captain· “Yeah. ”

1808:14 – First Officer: “Alright. now it’s coming. ”

1809:19 – 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 empty. ”

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 the request.

At 1810:47, the captain requested the flight’s distance from the airport. Portland Approach responded, “I’d call it 18 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. ”

A 1813:38, the captain said. “They’re all going. We can’t make Troutdale. ” (A small airport on the final approach path to Runway 28L. ) 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 naut mi east southeast of the airport. There was no fire. The wreckage path was about 1. 554ft long and about 130ft wide. The accident occurred during the hours of darkness at latitude 45 deg 31 min 21 sec N and longitude 122 deg 29 min 59 sec W. The elevation of the accident site was 285ft.

Injuries to Persons Fatal: crew. two; passengers, eight. Serious: crew. two; passengers. 21. Minor/None: crew. four; passengers. 152.

Damage to Aircraft. The aircraft was destroyed.

Other Damage. Two unoccupied homes were destroyed. Telephone lines were cut and high-tension electrical powerlines were damaged.

Throughout the landing delay, Flight 173 remained at 5000ft 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 13,209Ib per hour – 220Ib per minute. At the beginning of the landing delay, there were about 13. 334Ib of fuel on board.

A new type of fuel quantity indicating system was retrofitted to this aircraft on May 12, 1978. The retrofit was authorised by Change Order Authorisation No. 2-4849. With the new system installed. there are eight individual tank quantity gages. Each of these gauges has three digits which are seven-segment incandescent lamps. On these individual tank gauges. the digital reading is multiplied by 100 to obtain the total amount of fuel in the tank.

The totaliser gauge receives input from each individual tank gauge and displays the total fuel available on three digital readouts. However. this digital reading must be multiplied by 1000 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 gauges is 100. The smallest increment of change on the totaliser is 1000Ib.

Before the implementation of the change order. each individual tank gauge 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 totaliser gauge. 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 400Hz 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 compensators.

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 per cent 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 per cent of the plan.

Medical and Pathological Information. A review of the flight crew’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.

Fire. There was no fire.

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 five 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 their 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.

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 (1Land 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 downward and outward when opened. The movement of the door actuated the automatic inflation of the escape slide.

The slide from exit 1 L 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 1 R reportedly inflated inside the cabin and extended across the aisle and lodged against seat BC. 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 evacuation.

The escape slides were removed from the accident site and were examined on Jan 3 and on Jan 9, 1979. No discrepancies were found in the installation, maintenance, manufacture or design of the escape slides.

The evacuation was completed in about two min. Except for seats at rows 20 through 22. which were torn loose from the floor attachments, there was only a minor disruption of cabin furnishings aft of row 6.

The emergency lights provided adequate illumination during the evacuation.

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 for all engines. His inattention resulted from preoccupation with a landing gear malfunction and preparations for a possible landing emergency. 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. Air safety w/11 be featured In AADR from time to time as the reports of major aviation accidents are supplied to us by the United States National Transportation Safety Board.