Aircraft Accidents and Lessons Unlearned LX: Mohawk Airlines Flight 40

On June 23, 1967, Mohawk Airlines flight 40 (MA40), a British Aerodynamics Corporation (BAC) 1-11, registration number N1116J, departed Elmira-Corning Regional Airport (ELM) in New York (NY), flying the next leg to Harrisburg, Pennsylvania (PA) at 2:39 PM (14:39) eastern standard time. Eight minutes later, at 14:47, NY Air Route Traffic was monitoring MA40 when it disappeared from air traffic control radar scopes within three sweeps (one sweep = 12 seconds). An aerial search was conducted, the aircraft was found to have impacted terrain one mile east of Blossberg, PA.

The National Transportation Safety Board (NTSB) accident report, AAR-68/AG determined that, “… the probable cause of this accident was the loss of integrity of the empennage pitch control systems due to a destructive inflight fire which originated in the airframe plenum chamber and, fueled by hydraulic fluid, progressed up into the vertical fin. The fire resulted from engine bleed air flowing back through a malfunctioning nonreturn valve and an open air delivery valve, through the auxiliary power unit [APU] in a reverse direction and exiting into the plenum chamber at temperatures sufficiently high to cause the acoustics linings to ignite.”

There is no debate that the lower rudder, horizontal stabilizer and top two feet of the vertical stabilizer on MA40 separated, that before the separation, the rudder and elevator systems failed. The aircraft lost its vertical and horizontal primary controls before crashing – and this is incredibly important – within eight minutes of departing ELM. The accident crew, however, experienced problems three minutes earlier.

To be clear, this was an aircraft-related accident (caused by the aircraft), yet maintenance was not at fault because they were never informed of any problem. What was true – was factual – was that the previous flight crew intentionally failed to report problems they experienced on a previous flight.

Before the correct cause(s) of the accident are discussed, there are questions about other items noted from the investigation, such as: was there an APU fire warning or aft body overheat alarm? If so, did the fire warnings sound? The report mentioned that the APU’s fire bottle was located in the wreckage in the ‘empty condition’, but, “… there was no evidence … extinguishers had been discharged by activating controls located in the cockpit” (accident report page 23). Which squib was activated: the fire handle or the overheat? Since the cockpit voice recorder (CVR) kept recording until impact (pages 14 through 17, paragraph 1.11(b)), why did the CVR not record fire aural warnings? If the CVR did not record aural warnings, why did the NTSB fail to write about it, make no recommendations or findings?

Finding 10 (page 50) stated, “The fire burned intensely from the fuselage up into the vertical fin due to the updraft and the built-in chimney which existed in that area.” Built-in chimney? Updraft? What was this investigator talking about? The vertical stabilizer was a non-pressurized area; there was no ‘built-in chimney’ effect, no updraft. Oxygen was limited. The fire did not climb up the vertical stabilizer like a chimney flue. It would have been consuming anything flammable, such as anti-corrosion lubricants. It is odd that NTSB investigators refer to the vertical stabilizer as the vertical fin. An NTSB investigators’ unfamiliarity with aircraft nomenclature makes one wonder, if investigators did not know the basics, then what else did they get wrong?

It had been established that the accident crew knew something was wrong only five minutes into the flight. The extensive damage done meant the problem began before departure at Elmira, while they were still on the ground. Could the accident have been prevented? All evidence suggests it could have, that the accident’s root cause was cultural. Why? Because pilots from a previous leg did not bring the issue that led to the accident to the maintenance personnel – not at Elmira – but at Newark (EWR) airport. These facts were reported in the MA40 accident report: AAR-68/AG, though the NTSB investigators did not recognize that safety issues found on the EWR flight that should have been addressed in EWR at the time they occurred.

Beginning at MA40’s last moments. On page 16 of the accident report, five minutes (14:44) into the flight, while climbing to 16,000 feet, the first officer (FO) says, “It’s hard to tell what it is.” Eight seconds later the captain tells the FO to, “Pull back on your speed,” to which the FO replies, “I’m doing it.” One pilot immediately says, “There’s something screwy here,” and “… having a little control problem here.” It is obvious from MA40’s CVR transcripts that within five minutes of departure, MA40’s crew are seeing the beginnings of the accident.

On page 08 of the report were statements made by the interviewed flight crew (IFC) that flew N1116J into EWR airport earlier on June 23rd. Per the IFC’s statements, “During descent, at a point about 30 to 40 miles from the airport [EWR], the air delivery valve was opened and the number 1 MAC (master air conditioning control) valve selector was switched to the APU position, while the number 2 MAC valve selector was left in the open position. The captain explained that he did not switch the number 2 system from engine air to APU air in order to avoid the cabin pressure fluctuation normally associated with such a change.” Apparently, Mohawk allowed (required?) pilots to run the APU when operating below 10,000 feet of altitude. Why? Who knows? The NTSB investigators never asked. Stranger still, the IFC operated the APU while still 30 to 40 miles out from EWR. Was the APU supplying the air conditioning system? This could have over boosted the APU and damaged it.

The IFC continued: “When the aircraft was 4 miles out on final approach, a strong odor became evident throughout both the cabin and the cockpit. The first officer, who was operating the aircraft controls, then turned both MAC valve selectors to the off position, in order to prevent outside air from entering the air conditioning system. However, the odor persisted.” NOTE: “… the odor persisted” meant the IFC stated that the ‘strong odor’ did not come from outside and that they recognized that fact.

NOTE: In the 1960s, cigarette and cigar smoking were allowed in both the cockpit and cabin during flights. The ‘strong odor’ mentioned must have been pungent – and offensive – enough to have been noticed. Each aircraft odor, such as deice fluid in the air conditioning system, has a distinctly identifiable odor. A ‘strong odor’ that experienced pilots could not identify should have not only alarmed the IFC pilots, but it should also have pushed the IFC to report it and write the occurrence in the maintenance logbook (AML), especially since it ‘persisted’ with the MACs turned to OFF.

To be clear, a flight crew’s workload increased as the aircraft neared the field, especially in the 1960s where analog aircraft did not share the workload with pilots as digital aircraft do today. The odor must have been alarming in its not being recognized and/or offensive enough for the IFC FO to shut off the MAC valves. However, it was what happened next that was most concerning:

After landing the number 2 air conditioning fail light illuminated. The IFC captain decided – he decided? – that the light came on from an overpressure condition from the reversers. “The captain then reset [NOTE: the IFC captain reset] the number 2 system and left the number 2 MAC in the off position. As the aircraft slowed to taxi speed, both MAC valves were switched to the APU position, thus allowing APU bleed air to flow into both systems, and within 5 to 10 seconds the odor disappeared.”

Why did the IFC captain reset the number 2 system and not report it? Why did the IFC captain assume he was qualified to troubleshoot the ‘strong odor’ and reset the system? Did he write the strong odor up in the AML? On page 10, “Although the captain on this flight did not write up this occurrence in the logbook, he did mention it to the captain of Flight 40 when the crew change was effected at Syracuse.” What did the IFC captain say? How did he ‘mention’ it? Why did the IFC not write up the problem in the AML? What systems training had they received to make this decision?

The IFC’s unusual actions continued. At the gate in EWR, “After the aircraft was parked, the junior flight attendant opened the aft bulkhead door, at which point she saw the rear stairwell area behind the door was filled with a foggy mist which produced the same odor she had previously noticed in the cabin.”

When questioned further, the IFC stated, “… that they attributed the source of the odor and mist to the industrial area of Newark over which the aircraft was flown during the letdown and approach.” This reasoning was, in the least, questionable. It was irresponsible and demonstrated the IFC’s ignorance.

Mists do not – did not – form in unpressurized areas simply by flying over anyplace, let alone Newark, New Jersey. The BAC 1-11 stairwell was closed to atmosphere; it did not scoop air from outside and allow it to condense inside the unpressurized compartment. Mists, like the one in the BAC 1-11 stairwell, are caused by hydraulic or engine oil fluids – under high pressure – escaping from a pump, pressure line or component. This high-pressure fluid atomizes – turns into small droplets – in a stable atmosphere, like the BAC 1-11 stairwell. The mist and odor’s integrity would not have endured a 130-knot approach; a fragile mist would not have gotten into the aft stairwell intact and hung there inside … inside … the unpressurized tail stair area. In addition to the ‘strong odor’, the mist was conclusive evidence that there was a serious problem in the stairwell, that the ‘strong odor’ was actually the mist being burned on hot components.

Then, on pages 9 and 10, NTSB investigators absurdly decided to treat the IFC to a ‘sniff’ test, meaning NTSB investigators tried different smells to see if the IFC could identify the ‘strong odor’ with, e.g., “… burning matches, hairspray, lighter fluid, hydraulic fluid and aluminum.” Aluminum what? What adult could not identify the smell of burning matches? What adult did not have a wife, girlfriend, sister, mother or daughter who used hair spray? What adult could not identify lighter fluid? What commercial pilot did not know what hydraulic fluid smelled like? Maybe the investigators should have tried more likely odors, such as: burnt hydraulic fluid, burnt lubricants, or anything that would be alarming to a pilot while flying an airplane. It was unclear what this futile test proved.

Why was there a fire inside the vertical stabilizer of N1116J? Simply stated: Combustion. Why? Because combustion is best acquired through atomization; combustion is best maintained through a constant feed of atomized flammables. Carburetors burn atomized fuel, which burns quickly, evenly and completely in the cylinder. Turbine engines employ atomizing fuel nozzles that break down jet fuel to a flammable form. A ‘built-in chimney’ effect did not happen. Instead, hydraulic fluid or fuel atomized under high pressure, formed a mist. This would have burned hotter and more completely. Any aircraft mechanic knows mists form because of pressurized fluids escaping and atomizing. The IFC should have reported the incident to maintenance. The IFC had a responsibility to report it.

The point of culture is that pilots and mechanics have always had the responsibility of safety, of both passenger and aircraft. When decisions are made contrary to that point, then the air operator’s culture should be explored to see if the behavior went beyond the questionable party. The IFC pilots did not write up the mist or ‘strong odor’ in the AML. Were the IFC pilots completely oblivious to the mist’s serious nature or were the IFC pilots afraid they would break down in EWR? Either way, the decision was a bad one and MA40 crashed. The NTSB investigators had a responsibility to pursue these blaringly obvious questions. They did not. Instead, the NTSB excused the IFC’s behavior.

In later accidents, the NTSB would continue to demonstrate this naivete, this ignorance, of culture and excuse bad behavior because of it. This was demonstrated in accident reports for ValuJet 592, Fine Air 101, National Air Cargo 102, Air Midwest 5481, Atlas Air 3591, the NTSB’s input on the two B737-MAX accidents and many others. Like bad marksmen they keep missing the target and because of their poor aim, do not fix the fundamental safety issue(s). The NTSB, as well as other investigatory agencies, choose to pursue the irrelevant and ignore the important; they divert attention from what is hard and settle on what is easy.

The dismissal of bad behavior, the overlooking of obvious safety infractions, do not serve safety. MA40 was an aircraft-related accident. The MA40 accident was aggravated by cultural issues, internal or external to Mohawk Airlines. In addition, the NTSB has never understood maintenance-related accidents or how to employ root cause analysis.

The MA40 NTSB accident report read like it was called in, that no serious effort was made to draw attention to poor procedures and bad judgment. Mohawk flight 40 proved that ignoring root cause analysis and settling on probable cause led to safety failures that would repeat. Culture was ignored to safety’s detriment.