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Pan American World Airways 001

Accident Case Study

Taken in isolation, this accident is simply the case of a crew missetting their altimeters, confusing inches with millibars. But there is much more to it than that.

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.


Accident Report

  • Date: 12 June 1968
  • Type: Boeing 707-321C
  • Operator: Pan American World Airways
  • Registration: N798PA
  • Fatalities: 1 of 10 crew, 5 of 53 passengers
  • Aircraft fate: Damaged beyond repair
  • Phase: Approach
  • Airport (departure): Bangkok-Don Muang International Airport (VTBD), Thailand
  • Airport (arrival): Calcutta-Dum Dum Airport (VECC), India

Narrative

[Aviation Safety Network]

  • Pan Am Flight 1 was a round-the world flight from Los Angeles (LAX) to New York.
  • The Boeing 707, "Clipper Caribbean", was on a visual approach to Calcutta (CCU) when it struck a tree and crashed 1128m short of the runway.
  • Weather at Calcutta was poor with a 400 ft ceiling and less than two miles visibility in rain.
  • The crew of "Clipper Caribbean" misunderstood the pressure reported to them by air traffic control. They didn't set the QNH at 993 mb, but instead set the QFE at 29.93. This resulted in a difference of the indicated altitude of 360 feet. The airplane consequently descended below decision height with flaps extended to 50 degrees.

Analysis

The existing thoughts on this accident point to QFE versus QNH as well as confusing millibars (or Hecto Pascals) with inches. The aircraft "descended below decision height" on a visual approach. I'm not sure how they came up with a 360 foot difference. We clearly don't have all the facts here.

images

Figure: QNE / QNH / QFE, from Eddie's notes.

There is a lot of missing information, but given what is said about this accident:

  • 0.993 Millibars = 29.32 inches Hg

  • Setting 29.93 results in an error of (29.93 - 29.32) x 1000 = 610 feet.
  • VECC Elevation: 16 feet

Cause

What little exists "out there" points to the crew setting the wrong value in their altimeters and ending up flying below a safe approach altitude.

See Also:

Altimeter Settings

Crew Resource Management Culture

Controlled Flight Into Terrain

Metric Altimetry

References

I don't have any primary source material on this crash. Can you help? Please hit the "contact" button and let me know.

Revision: 2018011420170915
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