Aircraft Accidents and Lessons Unlearned LIX: Eastern Airlines Flight 304
On February 25, 1964, Eastern Airlines flight 304 (EA304), a Douglas DC-8, registration number N8607, departed New Orleans International Airport (MSY) for Atlanta Municipal Airport [later called Hartsfield airport]. The DC-8 took off into overcast skies in the early morning. At 02:05 central standard time, after acknowledging a request to change radio frequencies, the DC-8 crashed into Lake Pontchartrain. No final messages, beyond the radio frequency change, were heard.
The investigatory agency credited with investigating this accident was the Civil Aeronautics Board (CAB), the agency that regulated airline operations, which managed competition between airlines. It was abolished in 1985, no longer serving a purpose after Deregulation. The CAB itself did not investigate the accident but deferred to more knowledgeable persons who understood the aircraft, weather, aircraft maintenance and other conditions that would have had an effect on EA304.
This accident investigation report represented the limitations of the aviation investigative abilities of authorities at the time. The airline industry was still transitioning into the jet age; studies were beginning to understand the effects of turbulence and wind shear; aircraft accident investigation itself was evolving, using techniques only just learned, one of which was to recover the wreckage off the floor of a body of water. With an average depth of 13 feet and a maximum depth of 65 feet, Lake Pontchartrain, EA304’s impact site, presented many challenges for investigators, where the widely scattered debris field was under the lake’s surface.
There was an honesty to reports of this era. No one hypothesized without explaining that the report was based on best theories and well-thought-out testing. Pride and arrogance did not have any place; investigators knew where the boundaries were and did not cross. Accident reports, unless acknowledged, were based on facts – not opinion. Root cause analysis did not exist then as it does today; it would have been employed by EA304’s investigators if it had.
EA304’s accident report Probable Cause – there were no accident report numbers – stated, “The Board [CAB] determines the probable cause of this accident was the degradation of aircraft stability characteristics in turbulence, because of abnormal longitudinal trim component positions.”
Recovery from the bottom of Lake Pontchartrain took about forty-eight days. The review of flaps and landing gear showed all were fully retracted. No ‘signs of fire, explosion or structural failure’ were discovered. The engines were recovered, all had evidence of ‘severe disintegration at impact’. The report stated that the ‘recovered reverser assemblies indicated use of reverse thrust at impact’, however this may have been an editing anomaly even though the report stated that “reverse thrust is used in flight as a speed brake.
Weather at MSY at the time of the accident, “… predicted ceilings below 1,000 feet, light rain in the Pensacola-New Orleans area [a 200-mile area], improving to 1,200-2,500 feet as the low center moved eastward [toward Pensacola]. Turbulence was forecast at a scale of 6 [moderate] in occasional thunderstorms and light to moderate wind shear turbulence above 14,000 feet.”
Did weather have an impact on the accident? Unknown, but it may have played a part, especially the thickness of cloud cover.
The report mentioned a problem with the elevator system prior to arrival in MSY: “The pitch trim compensator (PTC) was inoperative, with a fix scheduled for the next morning at Kennedy airport.” JFK airport, which was renamed from Idlewild two months earlier, was the final destination of flight 304. The PTC, per the report has, as one of its functions, “… required in the low altitude, high speed regime below Mach effect to improve stick force characteristics as speed increases.” The PTC also applies nose-up control during high-speed flight, which EA304 had not reached before the accident.
As mentioned, the flight crew was aware of the PTC issue and expected that the problem was to be fixed in JFK the next day. On the accident aircraft’s maintenance log were five discrepancies, one of which was the PTC being inoperative. As it stood, the PTC should not have been a problem. But having been documented as being inoperative did not relieve those responsible from assuring the PTC was properly nullified, that the PTC could not cause a problem in its status as inoperative.
If the PTC failed in the extended position, the first officer (the flying pilot) could have been driven to trim the stabilizer ‘nose down’; this would have relieved the forces on the control wheel. To understand the consequences of not properly addressing the PTC before flight, assuring it could not negatively affect the pilot’s actions, it would be necessary to review the conditions during the accident flight, which lasted less than four minutes:
1. Night flight; no celestial lighting from the moon or stars.
2. Over a large body of water at 2:00 AM meaning little to no ground reference points.
3. Visibility near zero after entering the clouds.
4. Low altitude, low speed.
5. Normal radio conversation with no indication of urgency or concern.
6. Climb and approach have always been high crew workload times.
7. Ample opportunity for spatial disorientation.
8. The PTC would cause the pilot(s) to keep driving the trim ‘nose down’.
Would the crew, as a result of the PTC extending, have trimmed the nose down, resulting in a controlled impact with the water? There have been many cases where the flight crew became distracted during high stress portions of flight, e.g., Eastern 401, which led to tragedy. There was no read out of the cockpit conversation prior to impact to determine what they may have been focusing on, in or outside the aircraft. Any cockpit voice recorder transcript would have been inconclusive anyway; they usually are.
Despite the various aircraft systems not being recovered in whole, the left and right stabilizer jackscrews were recovered and showed that they were both ‘within one turn of the full AND [aircraft nose down] trim setting’.
Was the trim set at such an extreme per the weight and balance calculations? Per the report, the aircraft’s takeoff gross weight was 213,871 pounds. The ‘center of gravity (CG) of 25.2 percent was within the allowable limits of 16.5 to 32 percent’ of mean aerodynamic chord – the accident flight’s CG was roughly in the center of the CG envelope. The trim would not have been set for takeoff trim at such an extreme setting, especially with the CG so close to center of the envelope. The stabilizer trim would have been outside the CG envelope for takeoff with such an extreme AND position.
It was unclear if there was a trim alert for the DC-8 in 1964. If there was, it would have warned the crew that the aircraft was trimmed too far nose down, that it had exceeded the trim allowable range. It may have been that there was some warning, that the crew was made aware of the problem, and they were trying to determine what to do when the altitude ran out. If they were trimming from just past rotation, they may not have had enough altitude to recover and because of the lack of reference points outside, did not realize the desperateness of their situation until it was too late.
The CAB did not provide recommendations. There were other contributing factors that pointed to a trim error that resulted in a controlled flight into terrain. This still should have alerted airlines at the time, at least those operating the DC-8, to be aware of inoperative PTCs, to develop better procedures for disabling the PTC and to be fully aware of trimming beyond the allowable limit.
The trim jackscrews were trimmed beyond limits – that was a fact, no probable about it. One of the earliest examples of root cause analysis fixing a problem.