WPR16FA035

A total loss of engine power on takeoff, which resulted from a sudden over-temperature condition due to an improperly adjusted fuel control unit and the deteriorated condition of the fuel nozzles.

The airline transport pilot was taking the private-pilot-rated passenger on a local flight in the former foreign-military jet trainer. After the airplane was refueled, the pilot delivered his customary 1-hour safety briefing to the passenger. The pilot subsequently taxied the airplane to the airport run-up area and, after a brief pause, to the runway. As the pilot initiated the takeoff roll, a witness observed dark gray smoke coming from the engine exhaust. When the airplane was about halfway down the runway and about 100 ft above ground level, the engine experienced a total loss of power. The airplane maintained altitude until it reached the end of the runway, at which point it rolled left, descended rapidly, and impacted the ground. A postcrash fire erupted that destroyed the majority of the airplane. Postaccident examination of the airplane revealed no evidence of any preimpact anomalies with the airplane's control system; however, control continuity could not be confirmed due to the extensive thermal damage to the airframe. Postaccident examination of the engine revealed that thermal distress of the 2nd and 3rd stage turbine nozzles and blades led to failure of the 2nd stage turbine blades, which rendered the engine incapable of producing thrust. All the fuel nozzles were below factory allowable limits in terms of flow rate and spray pattern and failed the factory functional test procedure. The asymmetrically deteriorated conditions of the installed fuel nozzle set matched the asymmetrically deteriorated condition of the 2nd stage turbine nozzle.   The maximum metered fuel delivery pressure measured on the test bench for the fuel control unit (FCU) was 85 atmospheres (atm). The typical maximum metered fuel delivery pressure for a normally operating engine to produce maximum approved thrust is 48 to 50 atm of pressure with an absolute maximum fuel pressure of 65 atm. The FCU was adjusted back to 50 atm during the test, indicating that there was no internal fault with the FCU but rather it had been purposely adjusted to 85 atm fuel pressure.  A search of the maintenance logbooks did not reveal when or where this FCU fuel pressure adjustment occurred. During the inspection and engine performance run-up of the engine performed about 2 weeks before the accident, maintenance personnel should have noticed an overly high fuel pressure, but this did not occur, making it likely that the FCU was adjusted after the inspection. It is possible that whoever made this adjustment did not understand or appreciate the fuel nozzle condition and erroneously tried to increase the fuel pressure to compensate for the low flow rate of the fuel nozzles. The manual adjustment of the FCU to deliver an overly high fuel pressure combined with the deteriorated condition of the fuel nozzles likely led to the heat-deteriorated condition of the 2nd and 3rd stage turbine nozzles and blades within a short period of time. Further, two of the four thermocouples that sense exhaust gas temperature had failed, which increased the likelihood of an incorrect cooler-than-actual temperature indication in the cockpit. As a result, the pilot likely did not observe any indication of engine thermal distress before the power loss.

HISTORY OF FLIGHT On December 6, 2015, about 1407 Pacific standard time, an Aero Vodochody L-39C, N39AY, was destroyed when it impacted terrain near Apple Valley, California. The airline transport pilot and the pilot-rated passenger were fatally injured. The airplane was registered to and operated by Jettran LLC as a Title 14 Code of Federal Regulations Part 91 personal flight. Visual meteorological conditions prevailed, and no flight plan was filed for the local flight, which departed Apple Valley Airport (APV) about 1406. A friend of the pilot-rated passenger reported that the passenger was considering purchasing a partial ownership in another L-39 airplane that was based at his local airport. Additionally, the passenger was a fan of the accident pilot's performances in the Red Bull Air Races. After the friend introduced the passenger to the pilot, they arranged to fly together in the L-39. Witnesses reported that, on the day of the accident, after refueling the airplane, the pilot delivered a 1-hour safety briefing to the passenger inside the airport terminal. Subsequently, they boarded the airplane, and the pilot taxied it to the airport run-up area. After a brief pause, the pilot taxied the airplane to runway 18 and began a ground roll. One witness reported seeing dark grey-colored exhaust coming from the exhaust nozzle as the airplane began its takeoff roll. According to witnesses, when the airplane was about 3,400 ft down the runway (just beyond the halfway point), witnesses heard a "pop, pop, pop" sound, which was immediately followed by intermittent, bright orange flashes coming from the exhaust nozzle. Witnesses reported that the airplane was about 100 ft above ground level; multiple witnesses reported that they had observed the airplane reach an altitude of about 500 ft above ground level by this point during previous takeoffs. A witness reported that while the airplane appeared to have slowed down after the popping sound was heard, it did not appear to lose any altitude. As the airplane reached the departure end of the runway, it rolled into a left-wing-low attitude. Two witnesses reported that the airplane rolled 90° to the left. The airplane then descended rapidly, and the left wing impacted the ground followed by the nose. The wreckage slid and came to rest in the dirt between two taxiways, and a fire ensued. A photograph of the airplane's departure captured the airplane about 2,200 ft down the runway and showed the airplane airborne in a slight nose-up attitude with the flaps deployed and the landing gear extended. PERSONNEL INFORMATION Pilot A review of the pilot's logbook revealed that he had accumulated a total of 23,200.3 hours of flight experience of which 170 hours were in the accident airplane make and model. The pilot accumulated a total of 12.2 hours in the accident airplane between August 25, 2015, and November 20, 2015, which was the date of the last recorded logbook entry. The last entry in the logbook was a simulator flight in a Boeing 787 on November 20, 2015, and his last recorded flight in the accident airplane was on October 27, 2015, from APV to Reno Stead Airport (RTS), Reno, Nevada. The pilot had been a competitive air racer since 1990 and was active in the Red Bull Air Races from 2004 to 2009. He won the Red Bull Air Race World Series Championship in 2005 and again in 2007. A friend of the pilot who had known him for about 15 years reported that he worked with the pilot at Racing Jets, Inc. According to this friend, it was not unusual for the accident pilot to take passengers for rides in the L-39. It was customary for the accident pilot to conduct a 1-hour safety briefing with each passenger before departure. During this time, the pilot would address numerous safety items including: canopy operation, parachute deployment, safety belt operation, and the procedures for a manual bailout. The pilot's wife, a professional career pilot and former aerobatic pilot, stated that it was not uncommon for the accident pilot to deliver a 1-hour safety briefing before flying with a new passenger. During a flight with a new passenger, the pilot might let them fly, but he would normally follow them on the controls, and, should an emergency arise, he would immediately resume control of the airplane. Pilot's 72-hour History The pilot was a first officer for a major airline. According to the pilot's wife, he left their home about 1500 on December 3, 2015, and drove to Los Angeles International Airport (LAX) where he boarded a commercial flight to Sao Paulo, Brazil as the first officer. The return flight arrived at LAX at 0900 on the morning of the accident flight. According to the pilot's fellow crewmembers on the flights to and from Sao Paulo, the crew queried each other to ensure they had received adequate rest. A crewmember recalled that during the return flight to Los Angeles, the pilot had a total of two breaks consistent with the shift schedule. On his first break, he rested in a business class seat; however, the crewmember could not confirm if he slept during that time. During the pilot's second break, a 3-hour time period, he used the airplane's crew bunk. The crewmember surmised that the accident pilot was sleeping during this time as his bunk light was not illuminated. Another crewmember stated that he would have recalled if another crewmember had slept or not. Pilot-rated Passenger The pilot-rated passenger, age 42, held a private pilot certificate with an airplane single-engine land rating. He was issued a third-class medical certificate on May 20, 2014, at which time he reported a total flight experience of 377 hours and 0 hours in the previous 6 months. A copy of his logbook was furnished by a family member and indicated that he had accumulated a total flight experience of 409 hours. The logbook showed that he had not amassed any time in turbine engine aircraft. According to the passenger's friend, he was a general aviation pilot who flew airplanes equipped with reciprocating engines. The witness was under the impression that his friend was not going to fly the airplane on the day of the accident. AIRCRAFT INFORMATION According to FAA records, the single-engine, two-seat tandem airplane was manufactured in 1993. According to Aero Vodochody, the airplane was manufactured in 1983. It was issued an FAA experimental special airworthiness certificate in the exhibition category on February 23, 2003, and it was registered to Jettran LLC on December 16, 2014. The airplane was originally used as a military jet trainer, and it was powered by an AI-25 TL engine that was manufactured by Ivchenko (now Motor Sich). According to the manufacturer, the airplane was owned and operated by the Ukrainian military from 1991 to 2002, when it was decommissioned, transported to the United States, and repurposed as a civilian airplane. A logbook entry dated February 20, 2003, indicated that the airframe had accumulated 1,908 total flight hours, and the engine had accumulated 532 total hours. The airplane's records prior to entering service in the United States could not be located. A maintenance entry from February 20, 2003 stated that the ejection seat rocket motors and charges had been removed, and the ejection system was no longer operative. The airplane's most recent condition inspection was completed on November 23, 2015, at which time the airplane had accumulated 2,062 total flight hours. The logbook entry for the condition inspection showed that the right- and left-wing flight controls and the aft flight controls were inspected. Additionally, the elevators, rudder, wing flaps, and ailerons were lubricated. Engine History The AI-25TL model engine was designed for use in the L-39 military trainer, and its first flight occurred in 1968. About 2,900 L-39 airplanes were built between 1968 and 1992, and the airplane remains in operational service with several