Aircraft Accidents and Lessons Unlearned LVI: N47BA – Payne Stewart

N47BA

On October 25, 1999, at 12:13 central daylight time (CDT), a Sunjet Aviation Incorporated Learjet 35, registration number N47BA, impacted an open field in Aberdeen, South Dakota. At some moment amid the last recorded direction from air traffic control (ATC) at 08:27:18 CDT and 08:33:38 CDT, contact between ATC and N47BA was permanently lost; in that six minutes and 20 seconds, it was believed that N47BA suffered a rapid cabin depressurization that incapacitated the flight crew and everyone else onboard. Four air national guard (ANG) F-16s – two Oklahoma ANG and two North Dakota ANG – were diverted to intercept N47BA’s trajectory to assist and/or communicate with the crew. All attempts were unsuccessful; N47BA’s flight crew was unresponsive and unanimated. One ANG pilot followed N47BA as it spiraled to ground impact. The flight was operated under Title 14 Code of Federal Regulations (CFR) Part 135 Air Taxi and Commuter; the accident was assigned accident number DCA00MA005.

Often, in addition to major accidents, the National Transportation Safety Board (NTSB) has launched a major accident group to investigate a government official’s accident and, sometimes, an accident involving a celebrity. In this case, six fatalities resulted from the accident, including pro golfer Payne Stewart; the use of the letters ‘MA’ in the accident number DCA00MA005 denoted a major accident investigation. For this case, six NTSB major accident investigators were assigned to cover Recorders, Operations, Human Performance, ATC, Maintenance Records and Airworthiness. Possibly, one of the NTSB’s assignment confusions was to separate Maintenance Records (MR) from Airworthiness (A/W); both were the same subject; MR and A/W were investigated by non-maintenance investigators who wrote two separate reports that should have been organized into one. It was unclear who the Inspector in Charge (IIC) was, but he/she should have led the investigation and managed the efforts.

The NTSB provided the following Probable Cause:“The National Transportation Safety Board determines the probable cause(s) of this accident to be Incapacitation of the flight crewmembers as a result of their failure to receive supplemental oxygen following a loss of cabin pressurization, for undetermined reasons.” The report provided no data. Worse, it provided no viable probable cause.

There were two reasons this non-probable cause stood out. For one, the use of the term, “… as a result of their failure to receive supplemental oxygen”. What did this mean, their failure? The inability to ‘receive supplemental oxygen’ could have been due to no oxygen being available – a fault in the oxygen system; the rapid decompression occurring too quickly for the pilots to have donned their masks or the pilots delayed too long in donning their masks. Either way, it was presumptuous to apply ‘their failure’ to the pilots without considering equipment failure or making an effort to prove ‘their failure’.

The second concern was the phrase: “… for undetermined reasons.” For a major investigation, this made no sense. Title 14 CFR Part 135 is a large presence in the aviation industry. Separated into ‘nine [passengers] or less’ and ‘ten or more’ operators, Part 135 includes, but is not limited to: helicopter medical services, air tours, air taxi, cargo contractors, corporate aviation, and others that far outnumber airline certificate holders (Part 121). Part 135s often work hand-in-hand with Part 121 operators. The lack of attention to such an accident was dismissive of Part 135 operators.

To be fair, the NTSB report stated, “The full report is available on the NTSB Web site. See http://www.ntsb.gov/publictn/publictn.htm for details. However, a search of this address opened an NTSB page that stated, “Page Not Found. The page you’re looking for doesn’t exist.”

There was a docket for DCA00MA005, but the documents showed no coordination between the final report writer (the IIC?) and the separate specialty groups. The final report contained nothing from those specific areas. What was the point of an investigation when what was discovered was never included?

The Operations report shed little light on the event aside from what the various manuals and procedures dictated that were followed. The Federal Aviation Administration (FAA) Principal Operation Inspector had been found to be engaged in the operator’s surveillance, so no FAA problems. The function of certificate holder surveillance and accident investigations is to understand what was right, what went wrong and to document both for safety advocates to build upon. Their purpose, however, is to learn moving forward; how to avoid repeated mistakes and to develop safeguards to protect aviation’s future.

The Operations report shed little light on the relationship between the FAA and the operator, Sunjet Aviation. Were there training issues with donning masks during emergencies? If everything was positive, why did the IIC fail to report it? Why did the IIC assume the flight crew failed to receive supplemental oxygen? Why was the Operations report ignored? The Operations information became a wasted opportunity, a lost chance to improve. Any mistakes missed were likely to be repeated.

It is necessary to remark upon a detail noticed by the ANG pilots as they flew in close proximity to N47BA, that was the cabin and cockpit windows were frosted and obscured any view into the aircraft, an indication of rapid decompression. When the cabin pressure was ‘dumped’ in a moment, the humidity, having been exposed to a sudden drop in temperature (at altitude) in the aircraft, went from suspended droplets to a gaseous state abruptly; the rapid temperature drop caused the water vapor to freeze to any surface, including the windows, which were described as “opaque” with frost. If it was assumed window heat was selected ‘ON’, was it working? Would window heat have affected the inside of the window, or would the cabin’s sub-zero temperature have canceled out the window heat’s effects?

This rapid decompression could have been caused by another catastrophic event beyond a valve failure. The decompression could have been attributed to a structural failure, perhaps a repair patch to the pressure vessel or a blown pressure seal. The ANG pilots said they did not notice exterior damage, but that does not mean a repair concealed by a fairing could not have failed. ATC’s last direction to N47BA was to climb to 39,000 feet but per the report, ANG caught up with the aircraft at 44,000 feet. Was the altitude selected in error or did the flight director exceed the targeted ceiling? Low oxygen at that altitude equaled an oxygen-deficient cabin, quick disorientation, blackout and suffocation. It was unlikely anyone survived, even unconscious, 2-1/2 hours without oxygen before the crash.

The final report was brief, especially for a major accident. It consisted solely of a recap of the last flight – nothing else. It was not an accident report, it was a play-by-play reminiscent of a documentary. Nothing useful from any of the specialty reports made it to the final report.

The MR report was wanting; the investigator did not appear to know aircraft maintenance. Questions in the MR report concerning a specific outflow valve airworthiness directive (AD) was valuable but detailed maintenance going back to 1979 was elaborated on in explicit, useless detail. This type data filled pages with irrelevant information. Specific outflow valve AD data (the valve was installed) and the altitude limit tied to the valve (which was still enforced) should have been pursued. Needed attention should have been directed to other possible failures for the decompression. The focus of attention Maintenance demanded, but did not receive, became a point of frustration; the MR report was Quantity, not Quality. The MR should have been integrated into the A/W report where better analysis was performed.

The A/W report was well written and researched. The A/W investigator invested Systems knowledge into the A/W Chairman’s report, important data that should have made DCA00MA005 a positive effect on aviation safety. The A/W report’s information was more instructive on the possibilities, a lot more helpful to understanding what happened. However, the IIC’s final report ignored the A/W report.

All accidents are important; none should be discounted due to aircraft size or fatality numbers; no person of fame should demand more investigatory diligence than a private pilot. That being said, when a notable circumstance occurs; when a catastrophic event this uncommon transpires, one that called attention to both Operations and Airworthiness; to allow this investigation to close with a weak sigh was inexcusable. Was there no more conclusion for the IIC to put forth beyond, “for undetermined reasons”? Did the pilots err? Maintenance? Component manufacturer or overhaul facility? Was it a maintenance manual procedure written incorrectly? Even a guess or blindly throwing a projectile at a dart board would have produced a more constructive probable cause. The aviation industry will never know. They should have cried out or perhaps they fixed the problem in spite of the report. DCA00MA005 was a result of minimal effort. Operations and Airworthiness created two paths to follow but the IIC’s inexperience left the most important information ignored.

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