Aircraft Accidents and Lessons Unlearned LXV: Pan American Airlines Flight 526A

On April 11, 1952, Pan Am World Airways flight 526A (PA526A), a direct flight between San Juan, Puerto Rico’s Isle Grande Airport and New York International Airport at Idlewild, ditched in the Atlantic Ocean moments after taking off, approximately eleven miles from the airport. The Douglas DC-4 aircraft, registration number N88899, had a feathered #3 propeller and had reduced power on the #4 engine from mechanical problems. The flight crew resolved that the combined engine troubles made it impossible to return to Isle Grande airport, forcing them to ditch in the ocean. Aircraft accident report file number 1-0026 was investigated and written by the Civil Aeronautics Board (CAB), the precursor to the National Transportation Safety Board (NTSB).

The CAB’s probable cause: “The Board determines that the probable cause of this accident was (a) the company’s inadequate maintenance in not changing the No. 3 engine which resulted in its failure immediately subsequent to takeoff, and (b) the persistent action of the captain in attempting to re-establish a climb, without using all available power, following the critical loss of power to another engine. This resulted in a nose-high attitude, progressive loss of air speed and the settling of the aircraft at too low an altitude to effect recovery.”

What is apparent from reviewing this report was that the investigation of the maintenance items found in (a) of the probable cause was performed by an investigator who understood the maintenance side of an airline; an airline operating in the post-WWII era; and aircraft with early 1950s radial piston engines in the commercial airline industry. Findings 3 and 4 stated: “(3) The company’s maintenance department at San Juan should have been alerted to a dangerous condition when metal particles were found in the nose section of the No. 3 engine and, (4) Pan American’s Miami office, having received information regarding the No. 3 engine from the maintenance department at San Juan, should have issued instructions to San Juan that this engine be changed.”

It seems appropriate this month of January to point to improvements that best represents what PA256A meant to aviation. January is named after the Roman Italic deity, Janus who looked forward and backward simultaneously. It was because of the ability to look backward that accidents, like PA256A, benefitted aviation going forward. The circumstances of the PA256A accident were clear-cut, leaving no debate about the CAB’s findings from this accident. There was no archival information to review, the CAB report did not present misinformation or opinion. PA256A’s report was straightforward.

The regulatory and investigatory bodies were different in those days. The Civil Aeronautics Authority, through the Federal Aviation Act of 1958, later transferred regulatory responsibilities to the Federal Aviation Agency, later called the Federal Aviation Administration (FAA). Until the launch of the NTSB in 1967 nine years later, the FAA played a more prominent role in accident investigation and, more importantly, found facts behind accidents that led to root cause, though at the time, the term ‘root cause’ didn’t exist as obviously it does today in proper accident investigation.

Though terrible, an accident that nothing was learned from made/makes the tragic even more tragic. From ValuJet 592 to National Air Cargo 101, the fundamental causes – the root causes – of these and other accidents, continue to be lost to investigation mistakes. However, PA256A was different. PA256A was not just learned from, the findings and causes from PA256A were acted on.

In 1964, three years before the NTSB came into being, the FAA decided to review accidents from the 1950s, specifically maintenance-related accidents, like PA256A. The FAA planned to proactively address maintenance – also called Airworthiness – items, e.g., scheduled maintenance, component lifetimes, reliability, failure rates, the unnecessary disassembling of parts and even pre-1964 assumptions as related to maintenance. World War II and post war attitudes had been reactive; judgments made with pre-Deregulation thinking where airlines enjoyed subsidies and heavy government involvement in airline activities. As a consequence, this mindset later drove the airlines to deregulate, to compete on their own and not allow government to dictate how an airline makes money. The FAA then limited itself to regulate aviation safety and allow the airlines to be self-sufficient in commerce and less wasteful.

In order to accomplish its goal, the FAA had to oversee a complete revamping of how maintenance was performed, a rethinking of maintaining aircraft that would retire the ‘old ways’; maintenance-for-the-sake-of-maintenance was a poor model. Scheduled maintenance, not just of the aircraft as a whole, but down to the components and systems, had to be made more efficient, more practical, more effective … and, more importantly, safer. It was discovered that an accident’s primary causal factors were basic weaknesses in the maintenance program. The ‘more maintenance is better’ attitude had to change because it was, in fact, inducing failures.

Reliability became the focus; make the aircraft reliable and the safety would fall in place. Manufacturers, like Boeing, Douglas, Lockheed, Pratt and Whitney, GE and Rolls Royce, focused on reliability in their products; it became a selling point that promised airlines that the aircraft would meet the flight schedule because the technology could be counted on. Technology would play a focal role in industry success. As a result, maintenance could be planned as opposed to reacted to or being unnecessarily performed.

In 1964, the FAA initiated rulemaking to bring about the Continuous Airworthiness Program; it was later amended to the Continuous Airworthiness Maintenance Program, or CAMP. This program was put into regulation under Title 14 Code of Federal Regulations (CFR) Part 121 Subpart L and Title 14 CFR Part 135 Subpart J, not as a CAMP regulation but as the sum of a CAMP’s ten separate elements, including a continuing analysis and surveillance process designed to re-evaluate the operator’s CAMP and make improvements as the airline … and the industry … evolved.

The path to the CAMP was more involved than adopting new regulations and studying accidents, like PA256A. With aircraft like the B747, DC10 and L1011, the mindset was to build more reliability into aircraft. Maintenance Steering Group (MSG) -1 came out in 1968 followed by MSG-2 in 1978 and MSG-3 in 1980 through today. The MSG progression provided processes that contributed to improved maintenance intervals and tasks. These improvements were customized to meet an operator’s schedule without sacrificing safety. At the same time Advisory Circulars (AC) 120-16 Air Carrier Maintenance Programs and AC 120-17 Reliability Program Methods – Standards for Determining Time Limitations provided guidance to industry on how to design maintenance programs to meet their operations’ needs.

It is important to include a major contributor to the reliability direction taken by industry and the FAA. In 1978, the Department of Defense (DOD) funded a study that United Airlines’ employees conducted. The joint study of Reliability-centered maintenance was captured in a 500-page report presented in December 1978. It came to, among other important findings, two major conclusions: (1) There was no strong correlation between component age and failure rates and, (2) part removal for time-in-service, as in time-based maintenance programs, didn’t work for most components.

What did this mean? (1) meant that a component’s age did not dictate its failure. Parts being replaced on a time-in-service basis, e.g., a slat actuator, were being replaced and overhauled with a good part of their useful life still unmet. These components had many flight hours to go before failure; operators were wasting money overhauling parts prematurely and grounding airplanes for avoidable lengths of time. This practice also induced failures. (2) meant that while some parts or components were time-sensitive, e.g., aileron cables, most hard time components didn’t hold to this restriction. This allowed operators to keep components ‘on-wing’ until failure, a more reliable way of tracking component lifetimes.

The path from pre-1964 theories to post-1964 realities took many years to transition. There were many old dogs resistant to new tricks, but with the dawn of Deregulation and the emphasis on competition-based business models, the transition was not just necessary, it meant the difference between financially strong or being relegated to a page in aviation history.

As mentioned, the concept of maintaining an aircraft into reliability proved futile; reliability could only be designed into an aircraft. This was best demonstrated by looking at the B747. Originally designed as an analog, three-pilot airliner, the B747 evolved from the B747-100 through the -200, -300 -400 and finally the -8, as an engineering success story. Reliability of the analog B747s introduction in 1969 may have rarely rose above the mid-90s percentile with pre-Deregulation attitudes yet to be purged. The B747’s final hulls in 2022 had a continuous reliability of 99% or better.

The successful transformation of the B747 from a three-man cockpit to a two-man cockpit, analog to digital technology with more fuel-efficient engines is an example of how design created the reliability that airliners today enjoy. The B747 was so successful that it brought about its own sunset, helping to improve such advances as engine reliability to the point where twin-engine airliners could compete for the B747’s place in the industry.

Could a present-day NTSB accident investigator/engineer have gleaned the type of information from a maintenance accident as well as one who has worked as a mechanic in the industry? When the FAA looked back in 1964 to PA256A and other maintenance accidents, the rearview mirror cast a hard reflection of maintenance gone wrong. However, PA256A also demonstrated problems hidden from the inexperienced, issues that FAA airworthiness inspectors are acutely aware of, sides of aviation the NTSB ignores and refuses to recognize in investigations, namely: Maintenance Culture.

The FAA’s workforce is split into Operations and Airworthiness, aka maintenance, meaning more than half the FAA inspector workforce are airworthiness and deal strictly with maintenance issues, while the NTSB has no one dedicated to airworthiness. And here, if the crash of PA256A happened today, there would be no NTSB investigator who would have recognized the impact of Pan Am’s – or any airline’s – maintenance culture on the accident and as a major contributor to the tragedy.

PA256A was correctly investigated by what appeared to have been investigators with good maintenance experience, investigators who understood culture issues and dug out the root cause of the accident. This is/was what accident investigation is intended to do: Comprehend. The FAA’s success in bringing PA256A’s findings forward to spearhead successful reliability programs demonstrated why the FAA led in aviation safety. It is hoped the FAA will continue to maintain this high ranking for many years.