Figure: Airplane after fire burned through the top of the fuselage, from NTSB Report, Figure 2.

Eddie Sez:

The NTSB Report does a good job of relaying the events of Flight 797 but perhaps fails to emphasize a few key points:

The captain attempted a second reset of three popped circuit breakers even after noting he felt them pop as he pushed them. As it turns out, the resetting of the circuit breakers did not cause the fire, but the danger posed bears discussion:

  • In 1983, Air Canada policy allowed crews to reset circuit breakers multiple times if they were allowed to cool "about 3 minutes." I was flying an Air Force Boeing 707 at the time and its manual was about the same: [Technical Order 1C-135(E)C-1, pg. 1-57] "Circuit breakers may be pulled and reset without damage to the circuit breaker; however, circuit breaker pulling should be kept to a minimum."

  • These days most manuals are more like what appears in the G450 Aircraft Flight Manual, pg. 4 - 1] "Resetting "tripped" circuit breakers or cycling circuit breakers to recover or "re-boot" systems should be done only if the system is required for continued safe flight and landing."

The captain delayed the decision to land for six minutes after first being told there was a fire, in the hope that the fire would go out. It could very well be that had he decided to land immediately the results would have been very different.

  • The airplane was airborne for nearly 20 minutes after the captain was first informed there was a fire. The industry has had a philosophy change on fire and smoke and fumes elimination. Before it was fight the fire, land if you must. Now it is land as soon as possible, fight the fire if you can.

  • Had the decision been made earlier, many of the further complicating factors (electrical failures, ATC mishandled vectors, evacuation confusion because of smoke) would not have happened.

  • As a result of this mishap, the industry now mandates better fire warning systems, fire retardant interiors, and procedural changes to make help get the airplane headed toward landing sooner and to improve evacuation procedures.

I don't offer this in an effort to point fingers, only to drive home this point: if you don't put the fire out in four minutes you won't be able to and if you don't get the airplane on the ground in fourteen minutes you won't be landing on your own terms. When in doubt, land. More about this: Abnormal Procedures / Cabin Fire.

What follows are quotes from the sources listed below, as well as my comments in blue.


Accident Report


Narrative

[NTSB Aircraft Accident Report, AAR-86/02, page 1] On June 2, 1983, Air Canada Flight 797, a McDonnell Douglas DC-9-32, of Canadian Registry C-FTLU, was a regularly scheduled international passenger flight from from Dallas, Texas to Montreal, Quebec, Canada, with an en route stop at Toronto, Ontario, Canada. The flight left Dallas with 5 crewmembers and 41 passengers on board.

[NTSB Aircraft Accident Report, AAR-86/02, page 2]


Analysis

Figure: Diagram of aft lavatory, from NTSB Report, Figure 9.

[NTSB Aircraft Accident Report, AAR-86/02, ¶2.2] The evidence substantiates a conclusion that when the smoke was detected by the flight attendants, there was a fire located within the vanity and/or the toilet shroud in the lavatory.

Investigators ruled out the trash bin itself as a source of the fire but could not rule out the possibility that there was debris behind the bin and that a lit cigarette could have fallen in that space. They further concluded it was "unlikely that the flush motor was the source of ignition of the fire." They also concluded the flush motor wiring harness was unlikely to be the cause. The investigated the possibility of a generator feeder cable nearby could have shorted, while they had no evidence supporting this, the possibility "could not be dismissed."


Probable Cause

[NTSB Aircraft Accident Report, AAR-86/02, ¶2.3] Since the fire was already well established, the attempts to reset the circuit breakers had no effect on the sequence of events.

[NTSB Aircraft Accident Report, AAR-86/02, ¶3.1]

  1. A fire propagated through the amenities section of the aft lavatory and had burned undetected for almost 15 minutes before the smoke was first detected.
  1. The Safety Board count not identify the origin of the fire.

  2. The first malfunction to evidence itself to the flightcrew was the simultaneous tripping of the three flush motor circuit breakers, about 11 minutes before the smoke was discovered. The flightcrew did not consider this to be a serious problem.
  1. The source of the smoke was never identified either by the flight attendant of the first officer. The captain was never told nor did he inquire as the precise location and extent of the "fire," which had been reported to him. Crewmember reports that the first was abating misled the captain about the severity and he delayed his decision to declare an emergency and descend.

  2. Because of the delayed decision to descend, the airplane lost the opportunity to be landed at Louisville. Had the airplane had been landed at Louisville, it could have been landed 3 to 5 minutes earlier than it actually did land at Cincinnati. The delayed decision to descend and land contributed to the severity of the accident.

[NTSB Aircraft Accident Report, AAR-86/02, ¶3.2] The National Transportation Safety Board determines that the probable causes of the accident were a fire of undetermined origin, an underestimate of fire severity, and conflicting fire progress information provided to the captain.

There is an art to reading an accident report, especially one that involves more than one country and several companies that could be found liable. If you want to see what the real cause of an accident is, look at the recommendations. The purpose of the investigation, after all, is to prevent recurrence. From a pilot perspective we need to learn the lesson: "land the airplane as soon as possible, fight the fire if time permits." But what really caused the fire and what has been done to keep this from happening again?

[NTSB Aircraft Accident Report, AAR-86/02, §4] The Safety Board recommended on July 19, 1983, that the FAA:


See Also:


References

Advisory Circular 120-80, In-flight Fires, 1/8/04, U.S. Department of Transportation

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

NTSB Aircraft Accident Report, AAR-86/02, Air Canada Flight 797 McDonnell Douglas DC-9-32, C-FTLU Greater Cincinnati International Airport Covington, Kentucky, June 2, 1983

Technical Order 1C-135(E)C-1, EC-135C Flight Manual, USAF Series, 15 February 1966