It has been 10 years since the ValuJet DC-9 accident in the Everglades that cost the lives of 110 people and a considerable amount of money. The cost to the aviation industry was also high as a result of additional requirements imposed on the existing aircraft fleet.
During the course of any investigation, many issues and concerns must be explored so that they can either be eliminated or identified as contributing factors in the accident. I thought you would enjoy a discussion of a few that didn’t receive much attention outside the investigation process.
How many of you remember the early reports from eyewitnesses who said they saw the aircraft flying straight and level and then just nosing over and descending into the Everglades? As a result of those eyewitness statements, investigators made a considerable–and ultimately successful–effort to recover the aircraft flight controls and linkages, as well as the flaps and the hydraulic actuators and associated structure.
The aircraft was totally destroyed, with very few large pieces. As a result, investigators made a serious effort to lay out the pieces in approximately the position they would have been on the aircraft.
We also used the maintenance history to search for possible issues that could be involved with the physical evidence that we had uncovered. On this aircraft there were a number of previous pilot squawks involving the circuit breaker for the electric hydraulic pump. To implicate or eliminate the circuit breaker, associated wiring and the pump itself as factors in the accident we were required to locate as much of that system as possible and determine whether these components had any involvement in the onboard fire.
We also searched the aircraft history for ADs and Service Bulletins for any clues that could lead us to a probable cause. On this Douglas DC-9 there was an AD that involved the elevator electric trim system, which had caused problems on other aircraft in the past. This relay has the voltage and high amperage available to cause a serious problem if it were to malfunction.
Because of that AD we were required to find the relay, the associated wiring and the structure around the area where the relay is located. This was extremely important because this relay is located within the sidewall of the forward cargo compartment right side forward of the cargo door.
By this time we realized that the aircraft had experienced a large fire in the forward cargo compartment, and we needed to find the source. After locating pieces of the relay and the structure around the location where it is mounted, we were able to determine that there wasn’t any fire damage that would indicate that the relay started the fire.
We also had to explore the comments or concerns that the flight crew expressed before and during the event. The aircraft’s cockpit voice recorder revealed comments about a suspect battery charger that was indicating what the crew believed to be an abnormal charging rate. We located as much of this system as we could to determine if there was any way the battery-charging system was involved in starting the fire. We determined that there wasn’t any fire damage in the area where the battery and the charging system are located.
The flight data recorder also contained information that we had to explore before we could eliminate other possible causes, and sometimes this work can help prove another theory. For example, this aircraft’s flight data recorder indicated some unusual rapid and short altitude changes but contained no other data to support them. This required us to investigate the altimeters and the static system.
As we located the required structure and components, including all the static-system tubing, we realized that the back side of the static pickup had been exposed to high enough heat to melt the tubing. Further work locating the aircraft fuselage in this area revealed clear evidence of a fire that progressed up the sidewall on the left side into the cabin. This agreed with other indications of a large, high-temperature fire on the left side of the forward cargo compartment.
The NTSB is required to make recommendations to prevent a repeat, and in this accident we made a number of recommendations that have had a positive effect on flight operations.
First, passenger aircraft no longer ship hazardous materials. Also, fire-detection and -suppression systems are now installed in the cargo/baggage compartments of new aircraft and retrofitted on in-service aircraft.
Also, for years the new-entrant airlines started life with airliners passed down from the existing air carriers. Starting with an older fleet, a workforce drawn from diverse backgrounds and a parts inventory that is probably a little thin poses challenges that can be difficult to overcome.
Now most new-entrant carriers start with aircraft that are new or almost new.
One more benefit is the accident rate for these carriers. In terms of safety, the low-cost carriers are equal to and in some cases better than the legacy carriers. That is quite an accomplishment.