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Pan American World Airways 806

Accident Case Study

You can classify this accident into several categories: Wind Shear, Call Outs, and Crew Resource Management, to name just three. But those three categories miss the problem entirely.

To really get a feel for the cause of this crash, take a look of an excerpt from Robert Gandt's excellent book, Skygods:

Another Pacific island. Another dark night, with rain and gusty winds, and yet another instrument approach to a runway without an electronic glide slope. A Pan Am 707 plowed through the jungle short of the runway, then burned. Ninety-one people perished. By now it was clear to everyone, even the Skygods. The crash of Flight 806 on the island of Pago Pago brought to ten the number of Pan American 707s destroyed. Pan Am was littering the islands of the Pacific with the hulks of Boeing jetliners.

This was another incident in a series of 13, 11 of which pointed to a problem with the Crew Resource Management Culture at Pan American World Airways at the time. They were able to reverse this culture and became one of the safest airlines in the world.


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Photo: Pan Am 806, from "Air Crash May" on Twitter.

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Accident Report

  • Date: 30 January 1974
  • Time: 23:41
  • Type: Boeing 707-321B
  • Operator: Pan American World Airways
  • Registration: N454PA
  • Fatalities: 10 of 10 crew, 87 of 91 passengers
  • Aircraft fate: Damaged beyond repair
  • Phase: Approach
  • Airport (departure): Auckland International Airport (NZAA), New Zealand
  • Airport (arrival): Pago Pago International Airport, (NSTU) American Samoa

Narrative

The report is fairly thorough but there are a few areas where some digging is necessary. The assigned first officer had laryngitis so the assigned third officer occupied the copilot's seat and is called the first officer part of the time and third officer a few other times. The assigned first officer occupied the jump seat. The assigned third officer survived the crash at first, was interviewed, and his testimony cited as the first officer. He later died of his wounds.

This was the 12th crash of a Pan American World Airways Boeing 707, the 10th due to pilot error. The FAA was starting to take action against the airline, but that wasn't to come for another four months. Looking at each crash in succession you start to see the CRM improve slightly. In this accident, the assigned third officer, called the first officer in the narrative, did offer two corrections to the captain during the approach. First was a very diplomatic "You're a little high." Then came "turn to your right," which would have been appropriate since the localizer was offset from centerline. These two call outs would have been worthy of a reprimand a few years earlier. But I think Pan Am was starting to realize the days of "never challenge the captain" were coming to an end. Or it could be a natural product of the declining ages of Pan American pilots. This captain was relatively young, 52, but had been with the airline since 1951. The third officer was 43 and had been with the airline since 1966.

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Photo: ILS DME Rwy 5, Pago Pago, American Samoa, from NTSB Report, Appendix D.

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[NTSB Report, ¶1.1]

  • At 2311:55, Flight 806 contacted Pago Approach Control and reported its position 160 miles south of the Pago Pago airport. Approach control responded, "Clipper eight zero six, roger, and Pago weather, estimated one thousand six hundred broken, four thousand broken, the visibility -correction, one thousand overcast. The visibility one zero, light rain shower, temperature seven eight, wind three five zero degrees, one five, and altimeter's nine eight five."
  • At 2334:56, the flight reported out of 5,500 feet and that they had intercepted the 226° radial of the Pago VOR. The approach controller responded, "Eight- oh six, right. Understand inbound on the localizer. Report about, three out. No other reported traffic. Winds zero one zero degrees at one five gusting two zero."
  • At 2338:50, approach control said, "Clipper eight oh six, appears that we've had power failure at the airport." The first officer replied, "Eight oh six, we're still getting your VOR, the ILS and the lights are showing." At 2339:05, approach control asked, "See the runway lights?" The flight responded, "That's Charlie." The approach controller then said, ". . we have had rain here. I can't see them from my position here." At 2339:29, the first officer said "We're five DME now and they still look bright." Approach Control replied, "'kay, no other reported traffic. The wind is zero three zero degrees at two zero, gusting two five. Advise clear of the runway." At 2339:41, the flight replied, "Eight zero six wilco." This was the last radio transmission from the flight.
  • Five minutes after the crash the winds were 020 / 13 G 35. There is speculation that the winds could be indicative of a micro-burst, which wasn't a term in use at the time. But the winds before and after do not suggest a micro-burst along their approach path, but the increasing headwind does explain the why the aircraft went above glide path at first.

[NTSB Report, ¶1.8]

  • A full ILS serves runway 5 at Pago Pago. A nondirectional beacon and MM are located 1.7 and 0.5 nmi, respectively, from the runway threshold. The ILS glide slope is installed at a descent angle of 3° and is not usable below 138 feet because of the effects of the irregular signal reliability. The ILS localizer is offset to the right and crosses the extended runway centerline 3,000 feet from the runway threshold. The decision height for the approach was 280 ft.; 250 ft above field elevation. Postaccident flight and ground checks of ILS system, which included the use of a radio theodolite, showed no indication of a system malfunction or out of tolerance condition.
  • Although the ILS approach procedure requires that DME be used to establish the final approach fix (FAF), the DME is not available on the ILS frequency. Thus, the flightcrew is required to monitor the frequency on at least one radio receiver until passage of the 7 nmi DME fix (FAF) position.

[NTSB Report, ¶1.1]

  • According to the cockpit voice recorder (CVR), conversation in cockpit for the last 59 seconds of the flight was routine. The captain asked the first officer about visual reference with the runway, and the first officer answered that the runway was visible. Windshield wipers were turned on and the flaps were set at the 50° position, which completed the checklists for landing. The first officer stated during his postaccident interview that the only thing he had not accomplished which he should have was to change the No. 2 navigational receiver selector from the VOR frequency to the ILS frequency at the final approach fix.
  • At 2340:22.5 the first officer stated, "You're a little high." Four seconds later, a sound similar to electric stabilizer trim actuation could be heard from the CVR.
  • From 2340:20.5 to 2340:54, the radio altimeter warning tone sounded twice. At 2340:33.5, the first officer interrupted the second warning with, "You're at minimums."
  • At 2340:35, the first officer reported, "Field in sight." Seconds later, the first officer stated, "Turn to your right," followed by "hundred and forty knots." This the last communication recorded on the CVR. There had been no comments made by either the flight engineer or the pilot who occupied the jumpseat as to abnormalities in airspeed, altitude, or rate of descent indications. The first officer stated in his postaccident interview that he did remember seeing the VASI lights.
  • At 2340:42, the aircraft crashed into trees at an elevation of 113 feet, and about 3,660 feet short of the runway threshold. The first impact with the ground was about 236 feet farther along the crash path.
  • The aircraft continued through the jungle vegetation, struck a 3-foot-high lava rock wall, and stopped about 3,096 from the runway threshold. The aircraft was destroyed by impact and the subsequent fire.

Analysis

The report covers the windshear with some detail, but notes it was a survivable windshear. That is certainly true. Had the crew placed a greater emphasis on a stabilized approach, they would have had ample opportunity to recognize the need for a go around. But I think there is more to it than that.

The captain had been off flying status for more than a year and was likely to be a bit "rusty" in his instrument skills. It appears to me that a common thread in many of these Pan American pilot error accidents was that the captain wasn't as good as he needed to be, and the crew was reluctant to point that out. You would be right to argue that no sane copilot is going to willing accept an unrecoverable situation for fear of angering the captain. But I think this kind of culture beats other members of the cockpit crew to the point they stop actively monitoring because there is often very little to gain from doing so. The guy in the right seat was the "third officer" which is a nice way of saying he was a first officer in training. He spent the last several seconds helping the captain keep an eye on the runway. No one, it seems, was watching the flight instruments.

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Photo: Pan Am 806 Descent Profile (Civil Aeronautics Board)

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[NTSB Report, ¶1.5]

  • The captain had been off flying status from September 5, 1973, to January 15, 1974, for medical reasons. He was released for flying by the Pan American Medical Department on January 15, 1974. Captain Petersen underwent simulator training on January 16, 1974.
  • The captain's "A" Phase check was completed January 18, 1974, with the notations that he exhibited a good knowledge of systems and procedures and that the simulator work was "very well done throughout." In order to requalify in the B-707, he made three takeoffs and landings on January 19, 1974. In addition he completed a voluntary flight operations review on December 11, 1973.
  • This approach to Pago Pago was the first instrument approach the captain had flown in instrument meteorological conditions (IMC) since his return to flying status.

[NTSB Report, ¶2]

  • The CVR readout and the interview with the first officer established that runway was in sight when the aircraft was about 8 nmi from the runway threshold. The runway probably remained in sight during most of the approach.
  • The first officer commented five times during the approach, after the aircraft was within 7.5 nmi of the runway threshold, that he had the runway or the runway lights in sight. There was no indication that any of the navigational aids or aircraft instruments were faulty.
  • The aircraft descended about 500 ft. below the published minimum glide slope altitude of 2,500 ft. before the glide slope intercept point was reached. This placed the aircraft 180 ft. below the final approach fix altitude of 2,180 ft. These altitudes were confirmed by a CVR comment, "Two thousand", made about 1.5 seconds before the FAF callout. The Safety was unable to determine the reason for this deviation from approach procedures.
  • At FAF passage, the 7 nmi DME fix, the first officer's navigational receiver selector switch should have been changed from the VOR position to the ILS position; however, this was not accomplished. If the change had been made, as good practice would dictate, the first officer could have monitored the approach more efficiently and his navigational display would have been ready for crosscheck by the captain or crossover in case of the failure of the captain's instruments.
  • As the aircraft approached the glide slope, it continued through and above it as the captain started his descent. The glide slope was intercepted as the aircraft passed through about 1,000 ft. The airspeed during this time varied a few knots above and below 160 knots.
  • The Safety Board believes that the windshear was caused by the winds from the outflowing winds from the rainstorm over the airport as they were affected by the upsloping terrain around Logotala Hill. The windshear was evident by a sharp increase in airspeed and a shallowing of the descent path. Consequently, the aircraft went above the glide slope. The airspeed at this time was still about 160 knots. The sound spectogram showed that at this time, the thrust was reduced to apparently correct the high and fast condition.
  • As the aircraft passed Logotala Hill, it apparently came out of the increasing headwind or updraft condition and the positive performance effect was probably encountered. The thrust was well below that normally needed for a stabilized approach, and about 16 seconds before impact, the aircraft started a rapid descent of about 1,500 fpm.
  • The "little high" comment was at 2340:22.5, the rapid descent began at 2340:26, and the crash at 2340:42. In the next paragraph the report puts the focus on the windshear but the paragraph after that suggests the captain was simply pushing over to make the runway. I think the latter is probably the primary driver here.

  • Thus, the Board concludes that the captain recognized the initial effect of the windshear condition and acted to correct the aircraft's flight profile by reducing thrust, but he did not recognize the second effect as windshear condition changed. Consequently, the aircraft, with low thrust, responded to the changing wind by developing a high descent rate. The captain had at least 12 seconds in which he could have taken action to arrest the descent in time to prevent the accident. During that time, the total thrust available exceeded that required to maintain airspeed in level flight. That the necessary pitch attitude and thrust changes were not t applied only indicate that the flightcrew was not aware of the high descent rate and the impending crash.
  • Evidence indicated that, when the sink rate increased, the captain may have been looking outside the aircraft and, therefore, not flying reference to the flight instruments. At the time the sink rate increased to 1,500 the aircraft over an area of lights (known as a "blackhole"), a heavy tropical rainstorm was over the and moving toward approach end of the runway, and the first officer had the runway in sight.

Cause

[NTSB Report, ¶2] The National Transportation Safety Board determines that the probable cause of the accident was the flightcrew's late recognition and failure to correct in a timely manner an excessive descent rate which developed as a result of the aircraft's penetration through destabilizing wind changes. The winds consisted of horizontal and vertical components produced by a heavy rainstorm and influenced by uneven terrain close to the aircraft's approach path. The captain's recognition was hampered by restricted visibility, the illusory effects of a "blackhole" approach, inadequate monitoring of flight instruments, and the failure of the crew to call out descent rate during the last 15 seconds of flight.

See Also:

Call Outs

Crew Resource Management Culture

Stabilized Approach

Wind Shear

References

Gandt, Robert, Skygods: The Fall of Pan Am, 2012, Wm. Morrow Company, Inc., New York

NTSB Aircraft Accident Report, NTISUB/C/104-007, Pan American World Airways, Inc., Boeing 707-3215, N454PA, Pago Pago, American Samoa, January 30, 1974

Revision: 20180201
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