NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.
The pilot was appropriately rated to act as pilot in command of the airplane for the intended mission. There was no weather, air traffic control, powerplants, or airplane airworthiness factors in the accident. The accident pilot initiated an ejection at some point after the airplane departed controlled flight, however, the airplane's attitude and altitude were outside the envelope for a successful ejection.
While troubleshooting the lateral imbalance condition that was encountered immediately after takeoff, the accident pilot was aware of the maintenance involving the left fuel transfer valve motor two days prior to the accident flight and quickly concluded that he had a fuel imbalance. He also indicated in communications with the flight lead that he was not certain if he had verified the fuel load during the pre-flight inspection. The airplane was controllable at this point; however, he elected to continue the flight even after the flight lead recommended that he return to base. As the flight progressed, the accident pilot also indicated that he believed he had a transfer problem from the left side tanks, resulting in fuel burning from the right side and no fuel burning from the left wing tanks, thereby exacerbating the lateral imbalance as the flight continued. Although the pilot likely did not verbalize every switch change that he performed in the cockpit, some of the information that was relayed was inconsistent with the design of the fuel system, possibly indicating that the pilot's understanding of the fuel system was limited. The pilots initial training on the Hunter at ATAC was reduced in time, potentially causing some lack of full understanding of systems. Therefore, the accident pilot elected to continue to the mission area, about 140 miles from the departure airport, with a known fuel imbalance condition, contrary to the airplane flight manual and the flight lead's recommendation.
After the pilot did decide to return to base, he made no more statements about the stick position or controllability of the airplane nor did the pilot declare an emergency which would have been appropriate given his urgent situation. Although there was insufficient data to conclsively determine the reason for the departure from controlled flight, it is likely that the pilot continued to counter the "heavy" wing with opposite aileron until full authority was attained and he was unable to further arrest the roll. At this point in the flight, the fuel unbalance was significantly greater than the maximum unbalance limitation in the Hunter manual and so controllability, especially at slower speeds, would have been questionable. Additionally, it is possible that the pilot may have elected to extend the flaps early during the approach, which would have aggravated the roll tendency as also stated in the Hunter manual. This scenario could not be confirmed because there was no radio communications from the pilot during this time, nor could the flap position be conclusively determined in the wreckage.
ATAC did not have a crew resource management or aeronautical decision making training program in effect. If such a program had been in effect, it may have led the accident pilot to follow the flight lead's recommendation and return or divert rather than continue the flight and troubleshoot.
Two days prior to the accident, ATAC maintenance replaced left fuel transfer valve assembly. The mechanic that conducted the work had never performed this task and expressed difficulty and confusion with completing it and had to request assistance from other personnel. No type-specific maintenance training exists for the Hunter and all maintenance training is conducted on-the-job. Although ATAC did have the appropriate manuals on hand to guide the replacement, the maintenance personnel were not aware that they had the British manuals, and only referenced the Swiss French-language manuals, which they could not translate. No task cards, detailed step-by-step instructions for maintenance tasks, existed for the Hunter due to the legacy nature of the aircraft.
Examination and testing of the left fuel transfer valve assembly found there was no evidence of pre-impact failure of the motor even though the valve ball was found about 80 degrees outside of the normal range. This information, along with the information relayed by the accident pilot to the flight lead regarding his fuel indications, led the investigation to consider the possibility that the motor/valve combination was mated with the valve shaft rotated out of alignment. The design of the assembly is such that the motor and valve cases can only be mounted to the airplane in correct alignment when connected to the electrical cannon plug. However, the investigation found that the valve shaft could be rotated a full 360 degrees, and the motor drive key could be set in one of two positions and still allow the cases to mate. Although the mechanic stated that while he had some difficulty mating the motor and valve, he only needed to rotate the valve shaft a small amount during the mating procedure. The mechanic did not view the face of the valve to inspect the alignment markings with an inspection mirror, nor was there any specific task in the maintenance procedure to confirm the shaft alignment prior to attaching the motor. Examination of exemplar valves and motors found that there were combinations of valve shaft rotations that could result in the valve being driven to positions similar to that found in the wreckage and that would be consistent with the effects reported by the pilot. Therefore, it is likely that the valve motor did not fail during the accident flight, but was installed incorrectly on the valve assembly with the shaft out of alignment by 90 degrees or more, preventing normal fuel transfer.
An additional fuel system anomaly was also reported by the accident pilot. During the flight he informed the flight lead that the left inboard external tank quantity indications had reduced, consistent with obtaining some fuel transfer from the left side. However, the design of the fuel transfer system, using bleed air pressure to the outboard external tank first is such that there is no way for the outboard tank to be bypassed and not feed fuel, while still allowing the inboard tank to feed fuel. ATAC representatives stated that they had seen this occur before, but neither ATAC nor Lortie could explain the mechanism.
The pilot initially detected a fuel imbalance condition immediately after takeoff, however, this would likely be too early for any imbalance caused by the improper motor/valve installation to have affected the fuel balance. The flight two days prior to the accident likely emptied the right outboard tank, and a large amount of the right inboard, without depleting the left wing internal or external tanks. The lack of accurate quantity indications on the wing tanks, and the potentially confusing indications of the fuel loading panel, likely led to the incomplete refueling of the right outboard external tank prior to the accident flight. Adding the estimated fuel remaining from the previous flight with that uploaded by the fuel truck, results in an approximate 50 gallon (340 pounds) shortage in the outboard tank. The mechanic noted that the lights on the fuel loading panel were extinguished; however, the timer switch does extinguish the lights prior to the timer completing its cycle. The mechanic also stated that he tapped the tanks to confirm the quantity but this method is subject to significant error. In addition, the pilot noted during the accident flight that he was not certain of the fuel quantity prior to takeoff and so likely did not check the quantity of the external tanks during preflight. Therefore, the initial fuel imbalance was likely the result of an incomplete and improper fuel loading due to limitations of the fuel system design of the airplane and an incomplete preflight by the pilot.
The pilot's decision to continue the flight with a known fuel imbalance is a possible indicator of company culture of pressing to complete the assigned mission. On March 6, 2012 another ATAC fighter crashed, fatally injuring the pilot. In that accident the pilot was also likely pressing to complete the mission, leading eventually to the accident. ATAC did not have a crew resource management or safety-risk management program in place for its pilots at the time of these accidents; therefore, it is likely that the company culture did not support good aeronautical decision-making and risk management concepts. Following a recommendation in a Navy audit in June 2012, CRM training was established. Also, ATAC established an operational risk management (ORM) program in August 2012.
Additionally, since the flight was operating under Public Aircraft Operations the Navy was responsible for oversight of the company. The Navy contract, while setting some requirements for FAA certifications, did not specify to what standards the airplane, pilots, or maintenance program were required to conform. Thus, the oversight environment did not support a safety culture or standards that would be expected in other U.S. commercial aviation operations.