Human Factors involved in the crash of ValuJet Flight 592

A Human Factors Case Study
Submitted to the Worldwide Campus
In Partial Fulfillment of the Requirements of Course SFTY 320 Human Factors in Aviation Safety

Embry-Riddle Aeronautical University
October 2013
Abstract
On May 11, 1996, Flight 592 departed from Miami. It had pushed back from gate after a delay of 1 hour and 4 minutes due to mechanical problems. There were 105 passengers on board, mainly from Florida and Georgia, as well as a crew of two pilots and three flight attendants, bringing the total number of people on board to 110. At 2:04 pm, the DC-9 took off from runway 9L and began a normal climb. 10 minutes later the aircraft crashed into the Florida everglades with all hands on board lost. This Case Study will analyze and evaluate all contributing factors, with focus on the human factors, and propose solutions that would have kept the Liveware element from causing the accident.

Intro The crash of ValuJet 592 was an accident that gripped the nation. In a decade of low priced airfare, ValuJet was a house hold name for providing economical flights. The loss of flight 592 raised nationwide concerns over the airline industry; from maintenance practices, to management pitfalls among all of the low cost air carriers. 592’s crash also rocked the entire airline industry, and ultimately caused a loss of confidence by the majority of the public in economical airlines. It was a completely avoidable accident that was solely caused by an error chain of human factors.
The Accident On May 11, 1996, at 1413:42 eastern daylight time, a Douglas DC-9-32 crashed into the Everglades about 10 minutes after takeoff from Miami International Airport. The airplane, N904VJ, was being operated by ValuJet Airlines, Inc., as flight 592. Both pilots aboard, all three flight attendants, and all of the 105 passengers were killed. Visual meteorological conditions existed in the Miami area at the time of the takeoff. Flight 592 was on an instrument flight rules flight plan destined for the William B. Hartsfield International Airport, Atlanta, Georgia. (NTSB,1997) ValuJet flight 591, the flight preceding 592 which was on the same aircraft, was also operated by the accident crew. Flight 591 was scheduled to depart ATL at 1050 and arrive in MIA at 1235; however, ValuJet’s dispatch records show that it actually departed the gate at 1125 and arrived in MIA at 1310. The delay was because of unexpected maintenance work involving the right auxiliary hydraulic pump circuit breaker. Flight 592 had been scheduled to depart Miami for Atlanta at 1300. The cruising altitude was to be flight level 350, with an estimated time en route of 1 hour 32 minutes. The DC-9 weight and balance and performance form completed by the flight crew for the flight to ATL indicated that the airplane was loaded with 4,109 pounds of cargo. (NTSB, 1997) At 1404:32, the first officer made initial radio contact with the departure controller, advising that the airplane was climbing to 5,000 feet. Four seconds later, the departure controller told flight 592 to climb and maintain 7,000 feet. The first officer acknowledged that transmission. At 1407:22, the departure controller instructed flight 592 to “turn left heading three zero zero join the WINCO transition climb and maintain one six thousand.” The first officer acknowledged this transmission as well. At 1410:03, an unidentified sound was recorded on the cockpit voice recorder, after which the captain remarked, “What was that?” According to the flight data recorder, just before the sound, the airplane was at 10,634 feet mean sea level, 260 knots indicated airspeed, and both engine were operating normally. (NTSB,1997) At 1410:15, the captain stated, “We got some electrical problem,” followed 5 seconds later with, “We’re losing everything.” At 1410:21, the departure controller advised flight 592 to contact Miami on its frequency. At 1410:22, the captain stated, “We need, we need to go back to Miami,” followed 3 seconds later by shouts in the background of “fire, fire, fire, fire.” At 1410:27, the CVR recorded a male voice saying, “We’re on fire, we’re on fire.” About 10 seconds later, values consistent with the start of a wings-level descent were recorded. According to the CVR, at 1410:36, the sounds of shouting subsided. About 4 seconds later, the controller asked flight 592 about the nature of the problem. The CVR recorded the captain stating “fire” and the first officer replying, “uh smoke in the cockp… smoke in the cabin.” The controller responded, “roger” and instructed flight 592, when able, to turn left to a heading of two five zero and to descend and maintain 5,000 feet. At 1411:12, the CVR recorded a flight attendant shouting, “completely on fire.” At 1411:46, the first officer responded that the flight needed radar vectors. (NTSB, 1997)
At 1411:49, the controller instructed flight 592 to turn left heading one four zero. The first officer acknowledged that transmission. At 1412:45, the controller transmitted, “Critter five ninety two keep the turnaround heading uh one two zero.” There was no response from the flight crew. The airplane’s radar transponder continued to function; so, airplane position and altitude data were recorded by ATC after the FDR stopped. At 1412:48, the FDR stopped recording data. The accident occurred at 1413:42. Ground scars and wreckage scatter indicated that the airplane crashed into the Everglades in a right wing down, nose down attitude. (NTSB, 1997)
Securing and Investigating the Crash Site
The primary impact area was a large crater in the everglades. The crater was about 130 feet long and 40 feet wide. The majority of the wreckage debris was located south of this crater, in a fan shaped pattern. Some pieces of wreckage found more than 750 feet south of the crater. (NTSB, 1997) The majority of the wreckage had to be recovered by hand; placed on airboats then transported to a nearby area for decontamination from fuel and chemicals. The pieces were then transported by trucks to a hangar for identification and examination.
There were many difficulties faced by the accident investigation crew. Since the aircraft had impacted at a high velocity and high angle of impact it was a “smoking hole” type crash site. This meant much of the main fuselage had broken up completely and was buried deep in the swap. The crew also faced extremely adverse conditions. Do to the relatively small area of the crash site and the fact that the aircraft impacted at the beginning of its flight, the entire area was saturated in jet fuel. Investigators had to be sealed in protective chemical suits, completely covered head to toe. This became very physically difficult in the Florida heat. Armed snipers had to be positioned on rafts and boats following the investigators to protect them from indigenous animals including alligators. After much searching, both flight incident recorders were recovered.
The airplane’s structure was severely fragmented. Fewer pieces of the right forward fuselage skins were identified, and pieces from the right side were generally more fragmented. The majority of identified pieces were from the wing and the fuselage aft of the wing box. The tires and wheel assemblies from the landing gear system were also recovered. The tires exhibited numerous rips and tears. The main landing gear actuators were found in positions showing that they were still retracted during impact. Most of both the left and right wings were recovered. The left and right horizontal stabilizers were recovered in fragments, including center sections, spars, skin panels, and both hinge fittings. There were no marks that indicated pitch trim or elevator position at the time of impact. Several pieces of the rudder were recovered as well. The largest piece measured 57 inches by 43 inches. Passenger service units from the cabin were found with the oxygen masks in the stowed positions, indicating that there was not a cabin depressurization issue. Three hand-operated fire extinguishers were found, all with severe impact damage. (NTSB, 1997) Because of the impact damage, it could not positively be determined if the fire extinguishers had been used.
Analyzing Crew Actions
It is clear that both flight crew members were in a very serious emergency situation, with electrical issue, smoke in the cockpit, and fire in the passenger cabin. Even though the captain decided to immediately to initiate a descent and return to Miami, for approximately 80 seconds the airplane continued on a northwesterly heading (away from the Miami airport) while they waited for ATC vectors which would have taken then on a wide circle to the left and a gradual descent back toward Miami. (NTSB, 1997)
The NTSB evaluated the engine, electrical systems, and flight control malfunctions that occurred in the 80 seconds during which the airplane continued northwestward, away from Miami. The electrical problems that first made the flight crew aware of the emergency were likely the result of insulation being burned on the wires by the cargo compartment. Electrical system wiring is routed outside of the cargo compartment of the DC-9, in accordance with federal regulations which require the wiring not be located against the cargo compartment liner and to incorporate high-temp insulation. (NTSB, 1997) The flight crew's comments about the electrical problems indicate that the fire had probably already escaped the cargo compartment by 1410:12; though, it probably had not yet burned through the cabin floor at this time. The flight crew also made comments that reflected their concerns about these electrical problems. It is probable that these electrical issues took most of the pilots’ attention while they were also trying to make their emergency return to Miami.
Another malfunction began at 1410:26, as shouts from the cabin alerted the flight crew to the fire in there. According to FDR data, while the left engine remained at its normal thrust setting, the right engine's power was decreased to idle. This reduction in thrust was most likely an intentional act by the pilots to reduce power and begin their descent back into Miami. The activation of the landing gear warning horn at 1410:28 suggests that the flight crew still had reduced power of the right engine to idle; as the warning horn is activated by one or both throttle levers being positioned to the idle position. The pilots would not have intentionally reduced thrust on one engine only, so they must have been unable to reduce the thrust on the left engine due to fire damage on engine control located above the compartment. The inability to change left engine thrust, became one more distraction to the flight crew. (NTSB, 1997)
Due to the lack of evidence from the CVR, FDR, and the wreckage, the NTSB was unable to determine with certainty the reason for the loss of control of the aircraft. Examination of the wreckage did show that before impact the left side floor beams melted and collapsed. This condition would more than likely have affected the control cables on the captain's side. The first officer might have had to take over flying the aircraft, though all the remaining control cables could have been affected by distorted floor beams as well. With the continuing degradation of flight controls and structural damage to the cockpit floor boards, the overall loss of control of the aircraft was most likely do to flight control failure. (NTSB, 1997) It is also likely, due to the radio silence before impact, that both pilots became incapacitated from fumes and smoke from the burning fire.
Probable Cause / Oxygen Canisters
The NTSB determined the probable cause of the accident to be a fire which started from the aircraft’s class D cargo compartment that was initiated by the actuation of one or more of oxygen generators being improperly carried as cargo. This was a result of a failure of SabreTech to properly prepare, package and correctly label them as unexpended oxygen generators. It was also a result of ValuJet to properly oversee its contract maintenance program to ensure compliance with maintenance, training, and hazardous material requirements and best practices. The FAA was also determined to be a contributor for failing to require smoke detection and fire suppression systems in class D cargo holds as was recommended by the NTSB after a prior, similar accident. (Federal, 1998)
Before the accident SabreTech crews began replacing the expired and near-expired generators with new generators on other ValuJet aircraft. According to SabreTech mechanics, almost all of the expired or near-expired oxygen generators removed from the two airplanes were placed in cardboard boxes, which were then placed on a rack in the hangar.(USDOT, 1999) On the removed canisters identification tag, in the "reason for removal” section, the mechanics made various entries such as "outdated," "out of date," and "expired," all indicating that the generators had been removed because of a time limit or date being exceeded. According to the corporate director for quality control and assurance at SabreTech, 72 individuals logged about 910 hours against the work tasks described on work card 0069. (USDOT, 1999 ) SabreTech also did not follow a consistent procedure for briefing incoming employees at the beginning of a new shift, and had no system for tracking which specific tasks were performed during each shift. A mechanic who signed work card for the canisters stated that he was aware of the need for safety caps on the canisters and had overheard another mechanic who was working with him on the same task talking to a supervisor about the need for these safety caps. The other mechanic stated in a post-accident interview that the supervisor told him that the company did not have any safety caps available. Their supervisor stated in a post-accident interview that his primary responsibility had been issuing and tracking of multiple jobs and did not work directly with the generators. He stated that no one, including the mechanics who had worked on the airplanes, had ever mentioned to him the need for safety caps. (USDOT, 1999 )
According to mechanics, there was a great deal of pressure to complete the work on the aircraft on time, and they had been working 12-hour shifts seven days per week. He and another mechanic cut the lanyards from the generators that he removed to prevent any accidental discharge.. He stated that he didn't put caps on the generators, but placed the generators into the same cardboard tubes from which new ones had been taken from. He said that he placed them in a box in the same upright position in which he had received new generators. He said that although he did not see any of the generators discharge, he had worked with them at a previous employer and was aware that they were dangerous. This mechanic stated that his lead mechanic instructed him to "go out there and sell this job," which the mechanic interpreted as meaning he was to sign the routine and non-routine work cards and get an inspector to sign the non-routine work card. He said he looked at the work that had been done on the removal of the canisters, but was focusing only on the airworthiness of that airplane. (USDOT, 1999 ) Before shipping, a stock clerk reorganized the contents of the five boxes oxygen generators by redistributing the number of generators in each box, placing them on their sides, end-to-end along the length of the box, and placing about two to three inches of plastic bubble wrap in the top of each box. He closed the boxes and to each applied a blank SabreTech address label and a ValuJet label with the notation "aircraft parts.” (USAO, 1999 ) According to the stock clerk, he identified the generators as "empty canisters” because none of the mechanics had talked with him about what they were or what state they were in, and that he had just found the boxes sitting on the floor of the hold area one morning. He said he did not know what the items were, and when he saw that they had green tags on them, he assumed that meant they were empty. (USDOT, 1999) This act helped seal the fate of flight 592.
Human Factors Many human factors were involved in this accident. Most notably was the improper “safe’ing” of the oxygen generators. However, a culture of improper maintenance practices by SabreTech allowed for technicians and supervisors to become complacent and except that they did not have the proper caps and simply stored them anyway without further inquiry. The poor maintenance culture extended to the shipping department that simply boxed up the hazardous canisters without checking what they were or how they should be shipped. ValuJet’s lack of ramp training meant the boxes were not verified for content before loading them on their aircraft. (USAO, 1999) Actions by the pilots contributed as well; not questioning the “oxygen bottles” as the canisters were labeled as on the cargo manifest they signed for as well as not donning oxygen when there was the first indication of fire aboard the aircraft. Had both pilots been conscious there is a chance, albeit small due to the controllability issues they were experiencing, that they could have lessened the impact and increased the chance for survivability.
Solutions / Conclusion If either one of the companies had upheld a culture of by the book maintenance, at least one of the factors in the error chain would have been broken and this accident would not have happened. SabreTech failed on multiple points, including not just maintenance, technician rest, and shipping as well. This ultimately lead to the closing down of SabreTech. ValuJet failed to require personnel to monitor and verify what was actually being loaded on their aircraft. There was a settling of whatever company property was loaded they did not need to verify. With these practices being allowed it was only a matter of time before an accident happened.

References: NTSB, (1997). “Aircraft accident report, inflight fire, and impact with terrain” AAR97-06, Retrieved October 3rd, 2013 Mechanic in SabreTech Case Indicted for Contempt of Court". USDOT. October 13, 1999. Archived from the original on September 17, 2008. Retrieved October 5th, 2013. "Revised Standards for Cargo or Baggage Compartments in Transport Category Airplanes". Federal Register. 17 February 1998. Retrieved October 1st, 2013. US Attorneys' Office Ignores Critical Evidence in the Valujet Crash: Valujet admitted oxygen generators were to be returned". July 12, 1999. Archived from the original on November 31, 2007. Retrieved October 3rd 2013.