Las Vegas, NV, USA
N140EM
DOUGLAS TA-4K
The pilot of the experimental turbojet airplane, the lead airplane of a flight of two, was returning to the airport after providing combat training support. He led the formation to the overhead pattern, and shortly after the break to downwind, the engine lost power. The engine did not respond to throttle movements. The pilot started a turn toward the airport; however, he realized that he was unable to make the runway, so he turned left away from the runway toward a field and then successfully ejected from the airplane. The airplane subsequently struck terrain and was consumed by fire. No anomalies were noted during the initial airframe and engine examination that would have precluded normal operation. However, examination of the main fuel control (MFC) revealed foreign object debris (FOD) from a nonmetallic material inside the MFC unit. The material was identified as a nylon 6/6 material that was consistent with other seal material in the unit. However, all similar seal material inside the MFC was at its expected location. Further, the flow path made it unlikely that any nylon 6/6 material within the MFC could have migrated from known sources during the postimpact fire to where the FOD was located. Additionally, it was unlikely the nylon material was deposited into the MFC after the accident because examination of fuel components downstream of the MFC revealed no anomalies, obstructions, or nylon material. The MFC was rebuilt about 17 years before the accident, and the airplane had flown about 425 hours since then. It is likely that the FOD was part of an extra seal that was inadvertently installed or fell into the unit at the last maintenance overhaul. Subsequently, the FOD in the MFC eventually became positioned in such a way that restricted fuel flow and caused the loss of engine power.
HISTORY OF FLIGHTOn August 18, 2016, about 0739 Pacific daylight time, an experimental Douglas TA-4K, Skyhawk turbo-jet airplane, N140EM, was destroyed when it collided with the ground following a loss of engine power shortly after entering the traffic pattern at Nellis Air Force Base (LSV), Las Vegas, Nevada. The airline transport pilot sustained minor injuries. The airplane was registered to and operated by Draken International Inc., for the U.S. Department of Defense as a public aircraft in support of the U.S. Air Force and U.S. Navy. Visual meteorological conditions prevailed at the airport and a military flight plan was filed for the simulated combat training flight. The local flight originated about 0620. According to the pilot, he was the lead airplane of a flight of two aggressors, returning to LSV after completion of their Weapons School support flight in the Nevada Test and Tactics Range. The flight was uneventful until the formation break-up on initial, in the traffic pattern. The pilot led the formation to the overhead pattern for runway 21R, and shortly after the break to downwind, the airplane experienced a loss of engine power. The pilot reported hearing a loud "thump," then noticed the engine's rpm decreasing, and heard the engine surging. During this time, the engine did not respond to throttle movements. The pilot at first initiated a turn towards the airport; however, he realized that he was unable to make the runway and consequently turned left towards a field. He selected manual fuel control and thought the engine might respond but the rpm continued to rapidly drop. Once assured that the airplane would impact in the field, the pilot initiated a successful ejection and sustained minor injuries. The airplane subsequently struck terrain and was consumed by fire, about 1 mile north of the approach end of runway 21R. Witnesses reported observing the airplane on downwind, as being low and descending. Shortly thereafter, they observed the pilot eject and then the airplane descended rapidly towards the ground and upon impact, produced a large fireball outside the base perimeter. A review of surveillance video shows the airplane flying wings level at a low altitude and descending. A few seconds later, the ejection sequence was initiated and two chutes (one from the unoccupied back seat) were observed deployed. A couple of seconds later, the airplane impacts terrain. PERSONNEL INFORMATIONThe pilot held an airline transport pilot certificate with ratings for airplane single-engine land, multi-engine land, and instrument. He also held ratings for a flight instructor certificate in airplane single-engine and instrument. Additionally, he was type rated in the Boeing 737, and held an experimental airplane authorization for the Douglas Corporation A-4 Skyhawk. The pilot was issued a first-class airman medical certificate on August 15, 2016, without limitations or waivers. The pilot reported that he had accumulated 8,076 total flight hours, 230 hours in the accident make and model airplane, and had flown 211 hours in the last 3 months. He also had previously flown the General Dynamics (now Lockheed Martin) F-16 Fighting Falcon airplane for the United States Air Force and logged about 5,200 hours in it. AIRCRAFT INFORMATIONThe TA-4K Skyhawk was a swept-wing, two-seat jet airplane powered by a single Pratt & Whitney J52 turbojet engine that was manufactured in 1970 by the Douglas Corporation and later upgraded by Draken International Inc. The airplane was developed for the U.S. Navy and Marine Corps during the Vietnam war era. Maintenance was accomplished by Draken International Inc. A review of the maintenance logbooks revealed that the last continuous airworthy inspection was accomplished on July 29, 2016, at an airframe time of 6,850.2 hours. The engine had a total time of 3,211.5 hours, 428.7 hours since inspection, and 1,826.3 hours since overhaul. The airplane utilized a single Pratt & Whitney J52 turbojet engine that produced about 9,200 lbs of thrust. The J52 is a continuous flow, gas turbine engine which incorporates a split 12 stage, axial-flow compressor and 2 turbine stages. A 5-stage low-pressure compressor (LPC) is driven by a single-stage low pressure turbine (LPT) front compressor drive turbine rotor and a 7-stage high compressor (HPC) is driven by a single-stage high pressure turbine (HPT) rear compressor drive turbine rotor. The accident airplane had an engine write-up on May 18, 2016, for a thrust deficiency while performing acrobatic maneuvers. The write-up stated that the engine seemed like it was not producing the correct amount of thrust. Military (MIL) power, also referred to as full-power or 100% power, would only indicate 98% power, with a noticeable humming noise, and the airplane became slow during acrobatics with the normal power settings. As a result, maintenance accomplished an engine run to 75% and all engine parameters checked good. The write-up also stated that maintenance would monitor the engine for any trends at 75% power or greater. Fuel servicing records indicated that the accident airplane was fully refueled with 916 gallons on the morning of the accident. The fuel truck that serviced the airplane had a fuel sample tested after the accident, and the sample was within established standards. The airplane forms indicated 8,200 pounds of fuel was onboard, prior to the flight. According to the pilot, he confirmed that about 8,000 pounds of fuel was onboard the airplane during preflight. The pilot further stated that during the flight, the formation accomplished about 3 fuel checks in the area. According to the accident pilot's wingman, during the flight, after their area work was complete, a final battle damage assessment check with the lead airplane was accomplished, prior to returning to the LSV. The lead airplane reported 2,300 pounds of fuel and his status as the wingman was 1,800 pounds of fuel. Draken International Inc.'s operations procedures stated that the minimum fuel for the airplane was 800 pounds and emergency fuel was 500 pounds. Additionally, the fuel at initial or the final approach fix was 1,000 pounds. The aircraft's flight manual lists the following procedures for a Low Altitude Loss of Thrust/Flameout: Throttle – Check full forward. Zoom climb. If below 1,500 above ground level (agl) and 250 knots indicated airspeed (KIAS) - Eject. Throttle – Retard. Fuel Control switch – Manual. - If thrust is not regained immediately, proceed as follows: RAT (Ram Air Turbine) – Deploy Throttle - Ignition, then idle. (Monitor EGT for signs of relight). External Stores – Jettison, if required. Throttle – Cautiously advance. Below 5,000 ft agl – Nil engine response, eject. Above 5,000 ft agl – Airstart. (if time and altitude permit, establish 250 kts glide and commence airstart). The TA-4K aircraft flight manual stated: ejection is mandatory "when an engine flameout occurs below 1,500 ft agl and 250 kias," except when unusual circumstances clearly dictate otherwise. METEOROLOGICAL INFORMATIONA review of data from LSV, automated weather observation station revealed that at 0756 conditions were wind calm, visibility 10 statute miles, scattered clouds at 11,000 ft, temperature 30°C, dew point 9°C, and an altimeter setting of 29.91 inches of mercury. AIRPORT INFORMATIONThe TA-4K Skyhawk was a swept-wing, two-seat jet airplane powered by a single Pratt & Whitney J52 turbojet engine that was manufactured in 1970 by the Douglas Corporation and later upgraded by Draken International Inc. The airplane was developed for the U.S. Navy and Marine Corps during the Vietnam war era. Maintenance was accomplished by Draken International Inc. A review of the maintenance logbooks revealed that the last continuous airworthy inspection was accomplished on July 29, 2016, at an airframe time of 6,850.2 hours. The engine had a total time of 3,211.5 hours, 428.7 hours since inspection, and 1,826.3 hours since overhaul. The airplane utilized a single Pratt & Whitney J52 turbojet engine that produced about 9,200 lbs of thrust. The J52 is a continuous flow, gas turbine engine which incorporates a split 12 stage, axial-flow compressor and 2 turbine stages. A 5-stage low-pressure compressor (LPC) is driven by a single-stage low pressure turbine (LPT) front compressor drive turbine rotor and a 7-stage high compressor (HPC) is driven by a single-stage high pressure turbine (HPT) rear compressor drive turbine rotor. The accident airplane had an engine write-up on May 18, 2016, for a thrust deficiency while performing acrobatic maneuvers. The write-up stated that the engine seemed like it was not producing the correct amount of thrust. Military (MIL) power, also referred to as full-power or 100% power, would only indicate 98% power, with a noticeable humming noise, and the airplane became slow during acrobatics with the normal power settings. As a result, maintenance accomplished an engine run to 75% and all engine parameters checked good. The write-up also stated that maintenance would monitor the engine for any trends at 75% power or greater. Fuel servicing records indicated that the accident airplane was fully refueled with 916 gallons on the morning of the accident. The fuel truck that serviced the airplane had a fuel sample tested after the accident, and the sample was within established standards. The airplane forms indicated 8,200 pounds of fuel was onboard, prior to the flight. According to the pilot, he confirmed that about 8,000 pounds of fuel was onboard the airplane during preflight. The pilot further stated that during the flight, the formation accomplished about 3 fuel checks in the area. According to the accident pilot's wingman, during the flight, after their area work was complete, a final battle damage assessment check with the lead airplane was accomplished, prior to returning to the LSV. The lead airplane reported 2,300 pounds of fuel and his status as the wingman was 1,800 pounds of fuel. Draken International Inc.'s operations procedures stated that the minimum fuel for the airplane was 800 pounds and emergency fuel was 500 pounds. Additionally, the fuel at initial or the final approach fix was 1,000 pounds. The aircraft's flight manual lists the following procedures for a Low Altitude Loss of Thrust/Flameout: Throttle – Check full forward. Zoom climb. If below 1,500 above ground level (agl) and 250 knots indicated airspeed (KIAS) - Eject. Throttle – Retard. Fuel Control switch – Manual. - If thrust is not regained immediately, proceed as follows: RAT (Ram Air Turbine) – Deploy Throttle - Ignition, then idle. (Monitor EGT for signs of relight). External Stores – Jettison, if required. Throttle – Cautiously advance. Below 5,000 ft agl – Nil engine response, eject. Above 5,000 ft agl – Airstart. (if time and altitude permit, establish 250 kts glide and commence airstart). The TA-4K aircraft flight manual stated: ejection is mandatory "when an engine flameout occurs below 1,500 ft agl and 250 kias," except when unusual circumstances clearly dictate otherwise. WRECKAGE AND IMPACT INFORMATIONExamination of the accident site by the National Transportation Safety Board (NTSB) investigator-in-charge (IIC) revealed that the airplane impacted desert terrain at an elevation of about 1,926 ft. All major components of the airplane were contained within the main wreckage site. The airplane impacted the ground at a relatively shallow angle and on a magnetic heading of about 087°. After impact, the airplane continued to slide forward on the ground for about 30 ft and then struck and breached a concrete wall. The airplane continued to slide forward for about another 45 ft before coming to rest on its right side against a berm. A post-crash fire ensured, and the debris was mostly contained from the concrete wall to where the airplane came to rest. The fuselage sustained substantial damage to most of its right side, from the vertical stabilizer forward to the cockpit area. The left speed brake was extended. The right speed brake was separated but appeared to be fully extended. The cockpit and nose area sustained extensive damage due to impact with the wall and the post-crash fire. The manual flight control release mechanism on both the horizontal stabilizer and aileron hydraulic power pack was found in the manual flight control mode. The engine was observed to be mostly intact and lying on its right side. The first stage compressor blades near the 6 o'clock position, were fractured and bent rearward, with minimal rotational deflection (bent in the direction opposite rotation). The inlet guide vanes and inlet case exhibited ground impact damage and were buckled and fractured near the 6 o'clock position. The engine-driven generator was separated from the front of the engine and was recovered nearby. The engine's no. 1 bearing was exposed and observed to be shiny, intact, and undamaged. No apparent damage was noted on the second stage turbine airfoils. All but one of the Pt7 (total pressure) probes were intact. One Pt7 probe was observed to be fractured. All six, Tt7 (referred to as the exhaust gas temperature (EGT) probes), were intact. The burner pressure (combustion pressure) Pb line remained attached but was observed to be fractured just forward of the electrical disconnect junction box, located on the bottom of the engine. The engine's gearbox had separated from it mounting points but was still partially attached to the engine by tubing. The engine's tailpipe was partially separated just aft of the rear engine flange. The engine was removed from the wreckage and further examination revealed that the left side of the engine was encased in molten metal. The main upper tower shaft was recovered nearby. A Pratt and Whitney investigator began a partial disassembly and examination of the rear portion of the engine, while on site. A follow up engine and airframe examination was accomplished at the salvage facility of Air Transport, in Phoenix, Arizona by the NTSB IIC. Engine representatives and investigators from the NTSB, Pratt and Whitney, Draken International Inc, and Boeing, were in attendance. A comprehensive borescope analysis of the engine was accomplished. The front of the engine was accessed, and multiple viewing revealed no foreign object damage (FOD) or blade tip interference. Access through an ignitor port allowed a view of the no. 4 and no. 3 combustion cans and several 1st stage turbine blades and vanes. No anomalies were noted. No damage to the turbine section was observed. A borescope was inserted through the tower shaft cavity towards the engine centerline and no anomalies were observed with the no. 3 bearing. All bearings were unremarkable with no discoloration or surface anomalies observed. The gearbox assembly exhibited damage consistent with ground impact and had separated from the engine mounts. The gear train was exposed due to large fragments of the housing being separated. Visual examination of the gearbox revealed no damage attributed to operation prior to impact. Housing damage prevented the gear train from being manually rotated. The gearbox was disassembled and examined. The drive shafts and gear teeth of the tach drive, the fuel pump, main bevel, and fuel control gears were all intact. The only anomaly noted was the fracture of the lower tower shaft cup which is part of the main bevel gear assembly. The lower tower shaft cup was separated from the rest of the assembly and about 40% of its engagement teeth were missing. The shaft was also bent about 60° Several cockpit instruments were removed and shipped to the NTSB's Material laboratory for examination. The instruments had sustained thermal damage and had various levels of damage from impact. No reliable information that was pertinent to the investigation was obtained from the instruments. The engine parts and accessories were
Foreign object debris in the engine's main fuel control unit, which restricted fuel flow and subsequently resulted in the loss of engine power. Contributing to the accident was the installation or addition of an extra seal during the main fuel control unit rebuild.
Source: NTSB Aviation Accident Database
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