17 Year Old FOD and a TA-4K Ejection (Draken International Skyhawk N140EM, Las Vegas)
On 18 August 2016 an ex-RNZAF Douglas TA-4K Skyhawk of Draken International, registered N140EM, was destroyed following a loss of engine power shortly after entering the traffic pattern at Nellis Air Force Base (LSV), Las Vegas, Nevada. The pilot ejected and sustained minor injuries.
The aircraft, which impacted the ground near Las Vegas Motor Speedway, was operated as a Public Aircraft supporting the 57th Adversary Tactics Group, USAF with Dissimilar Air Combat Training (DACT). Public Aircraft are effectively the FAA equivalent of a civil ‘State Aircraft’, to use ICAO terminology. Exercise Red Flag 16-4 was under way at the time, and a pair of Draken A-4s had been exercising with 4 USAF F-16s.
The Accident Flight
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.
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…at a relatively shallow angle…
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.
Safety Investigation: Engine Shop Component Overhaul Build Debris
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.
The A-4 series was equipped with Douglas Escapac ejection seats. The TA-4K had the IG3 variant.
The ejection sequence appeared to function normally, and no anomalies were observed with the equipment. A review of the ejection seat assembly revealed that all inspections and time change requirements were current, with the exception of the separation rocket motor inspection, which were due on both ejection seats in July 2015. However, an extension of the inspections, was approved by the FAA, with the manufacturer’s assessment memorandum.
Investigating the power loss…
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.
NTSB Probable Cause
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.
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