Aircraft Accidents and Lessons Unlearned LXXIII: Trans World Airways Flight 529

On September 1, 1961, a Trans World Airways (TWA), Flight 529 (TWA529), a Model 049 Lockheed Constellation, registration number N86511, crashed nine miles west of Midway Airport, Chicago, Illinois. The flight, which originated in Boston Airport and was scheduled to terminate in Los Angeles Airport, lost longitudinal control during climb out from Midway five minutes into the flight. The Civil Aeronautics Board (CAB) investigated the accident. There were no assigned accident or report numbers used at the time.

NOTE: The CAB was the original aeronautical agency under the Department of Commerce. Before it was dissolved in 1985, responsibility for aviation duties had been given to the Federal Aviation (F-A) Agency in 1958, which later became the Federal Aviation Administration (FAA). Aircraft accident investigation duties were transferred to the National Transportation Safety Board (NTSB) in 1967.

The elevators on the empennage of the Lockheed Constellation

The CAB determined, “… that the probable cause of this accident was the loss of an AN-175-21 nickel steel bolt from the parallelogram linkage of the elevator boost system, resulting in loss of control of the aircraft.” The fact nickel steel was the AN bolt’s material was not relevant for the purposes of this analysis, except for the fact the bolt missing from that position was supposed to be an AN-175 nickel steel bolt. There weren’t differential corrosion issues or any other contributing factor that could’ve led to the bolt missing beyond the fact it had unintentionally separated just prior to the accident.

Per the report, the parallelogram linkage from which the bolt was missing was, “… the pilot elevator input to the control valve of the elevator boost system.” Examination of the linkages showed there wasn’t any damage, such as hole elongation, or corrosion that contributed to the bolt and its attaching hardware to be missing; no metal fatigue allowed the bolt to slip out of the linkage.

The elevator boost package and missing AN-175-21 bolt hole.

The report’s analysis determined the bolt was not lost during impact. Questions of washers as part of the attaching hardware were brought up at the hearing, where a TWA mechanic stated that one of two washers used was not installed under the bolt head because the nut couldn’t be installed and secured. The alternate method would’ve been to use a longer bolt, which would’ve had interfered with the linkage’s movement. Whether this was a safety issue wasn’t determined. Since the linkage hole didn’t show damage, it was clear the bolt had not pulled through the hole where the missing washer was used.

All evidence of how the boost system works, made the case for the bolt backing out before or during climb. The report referred to a military version of the Constellation where a clevis bolt backed out of the parallelogram linkage to the spool. Though this was a different bolt, the resulting control issues were identical. The CAB showed the bolt, missing before impact, led to the boost system failure. The missing bolt was what caused the accident. However, it wasn’t the Cause of the accident.

It is of interest the accident aircraft didn’t have a cockpit voice recorder (CVR) or flight data recorder (FDR). Yet, with its less sophisticated (by today’s standards) investigatory methods, CAB investigators successfully employed straight forward analysis. Observant investigators determined the missing bolt led to the accident from the evidence available. CAB investigators didn’t dismiss aircraft mechanic testimony. Investigators weren’t hindered by missing FDR and CVR data. The investigation, from accident to report publication, took 15 months. All evidence was retrieved from the impact site by those who knew how to read the debris field. TWA529 was an analog accident investigation; the aircraft had mechanical flight controls. The investigation was achieved without an FDR, CVR or cockpit camera, which proves such devices are simply tools – not critical investigatory necessities; they provide good data, but the information can be ambiguous, deceptive, or useless if given too much trust.

On November 22, 1961, the CAB recommended to the Administrator of the F-A Agency, “… that the mechanism for shift-to-manual in the Constellation boost system be modified so that the actions would be sequential rather than simultaneous.” In addition, “On March 8, 1962, the Administrator advised the Board [CAB] that his agency was having the Constellation Flight Manual amended to include procedures for turning off the elevator boost with an uncontrollable elevator.” The recommendation was well researched, the means to make the modification successful was understood by all parties. There wasn’t any political or bureaucratic disconnects between the CAB and the F-A Agency.

Without the accident aircraft’s linkage bolt to examine, the CAB was left to assume the bolt was installed correctly – there was no evidence to the contrary. They interviewed a TWA mechanic in the hearing and learned the washer might not have been installed under the bolt head, but the mechanic couldn’t determine if he worked the accident aircraft and its boost linkage installation.

Although the CAB did solve what caused the accident, the CAB didn’t find the Cause of the accident, namely why the bolt either fell out, wasn’t installed correctly, or failed. Was there a problem with TWA’s and/or Lockheed’s training programs? Did the missing washer contribute to the bolt falling out? Was the bolt ever locked in position with a cotter key or safety wire? If not, how to prevent another event.

If the CAB took a hard look at TWA’s Constellation maintenance procedures, the results never ended up in the report. Could the CAB have identified maintenance issues to prevent other accidents? Possibly. They did have their heads in the game. Should the CAB have isolated maintenance or manufacturer problems? Yes. However, despite the fact the CAB didn’t have modern investigatory technologies that are available today, their work was impressive and proactive. While the CAB report contained unambiguous information that made real safety improvements, there was still the question of the Cause.

On April 1, 1965, Title 14 code of federal regulations (CFR) Section 121.371 Required Inspection Personnel was adopted. This regulation dictated air operators create an inspector position that provided a second set of eyes for certain maintenance procedures, such as flight controls. Installations would now require two signatures: the mechanic and an inspector. This positive safety enhancement was one of ten regulatory elements under subpart L, the air operator’s continuous airworthiness maintenance program. These regulations met industry changes, guaranteeing – if followed – TWA529 would not repeat.

If followed.

Which it wasn’t, resulting in six fatal industry accidents. On February 16, 2000, Emery Air Freight Flight 17, a Douglas DC-8-71 in Sacramento-Mather Airport in Sacramento, California, crashed. The analysis can be found at: https://www.aviationlessonsunlearned.com/blog/aircraft-accidents-and-lessons-unlearned-viii-emery-17. In Emery 17, the right-hand elevator tab bolt separated from the armature connecting the elevator to its elevator tab. During the investigation it was found Emery’s mechanics removed the bolt but didn’t install it with an inspector present.

Then on January 8, 2003, Air Midwest flight 5481 also crashed, in part because both the mechanic and inspector didn’t perform their functions correctly. This analysis can be found at: https://www.aviationlessonsunlearned.com/blog/2018/7/10/blog-headline-n86f9

What, then, does TWA529 teach us over sixty years later? Why were the CAB’s investigatory processes so successful as compared to today’s investigations?

What is happening with every aviation accident is the Cause is being lost, indeed ignored. Investigators are taking credit for mis-directions, which lead to experience and knowledge vacuums, perpetuated as each new class of investigator is trained in the wrong procedures. Accidents aren’t being prevented, all that’re changing are the contributors to the accidents. What root cause that led to TWA529 now shows up as an aircraft fire, an out of balance condition, and/or an engine failure.

Furthermore, educational institutions, such as Title 14 CFR Part 141, Part 142, and Part 147 aviation schools and training centers – even FAA training facilities – aren’t teaching accident root cause analysis. Instead, they teach what caused the single accident – nothing more. This leads to safety resources being misrouted and agencies drawing incorrect conclusions. All investigatory attention is diverted to one accident – one aircraft – one flight – ironically, one that wasn’t prevented. Ignored are the many accidents that are preventable. What a waste of time and resources.

The NTSB focuses all investigatory resources to the accident at hand. While sadly tethered with the absurd solution ‘probable cause’, NTSB investigations have not only missed multiple safety items, their short-sighted attempts at ‘safety improvements’ have led to wasting millions (billions?) of dollars on insignificant modifications. Myopic recommendations have led to litigious mistakes that cost aviation businesses the ability to improve safety and technology, even as fatalities continue to rise from the NTSB’s missed findings.

The NTSB consistently fails to provide the Cause – root cause – of the accident. The Cause of ValuJet 592 wasn’t oxygen generators. The Cause of National Air Cargo 101 wasn’t shifting cargo. The Cause of Air Midwest 5481 wasn’t mis-rigged elevators or the center of gravity falling outside the flight envelope. The Cause of Emery 17 wasn’t the missing elevator tab bolt. The Cause of Fine Air 101 wasn’t cargo restraints.

Because the NTSB chooses to settle for probable cause instead of root cause, the educational institutions are leading new pilots, mechanics, and air traffic controllers to arrive at the wrong conclusions. Worse, even FAA course specialists are providing each FAA aviation safety inspector (ASI) with the wrong information about accident investigations; misdirecting ASIs to ignore facts and focus on casualties; diverting attention from safety enhancements that could improve the safety of their certificate holder.

Inexperienced FAA course specialists are buying into the NTSB’s version of probable cause. This a major problem. Some FAA course specialists have zero industry experience and no knowledge about the topic they’re writing about. Many course specialists have never flown a commercial airplane or even turned a wrench. As a result, the FAA and the industry is becoming like the NTSB: inexperienced, unknowledgeable, and arrogant. This must change.

TWA529 advanced safety, not with just the Constellation but also with later airliners that could have suffered from the same mistakes. The CAB showed its quality: The best. Aviation is stronger – and safer – for the integrity the CAB showed.