The Air Force blamed a chafed electrical wire for causing an F-22 fighter jet to crash Nov. 15 at Tyndall AFB, Fla., according to the service’s accident investigation board (AIB) report.
Air Force Col. Todd Flesch, president of the AIB, said in his statement of opinion a chafed positive generator feeder wire arced, pierced an adjacent hydraulic line and started an inflight fire in the aircraft’s left airframe mounted accessory drive (AMAD). When the generator feeder wire arced, the system sensed the initial arc via its electrical feeder fault protection, causing the left generator to shut down. When the pilot attempted to restart the generator in accordance with standard procedures, the ensuring arc ignited the misting hydraulic fluid and provided a fuel source that sustained the fire.
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| The Air Force’s F-22. Photo: Lockheed Martin. |
The fire started in the left AMAD bay and affected components throughout the entire AMAD bay during the pilot’s recovery, Flesch said. The ensuing fire and heat compromised critical aircraft electrical and hydraulic systems that control the F-22A flight control surfaces and led to an unrecoverable flight state. The pilot initiated a successful ejection approximately 20 minutes after the fire started and the aircraft impacted the ground at 3:33 pm EST.
The Air Force also blamed the weather, saying it “substantially contributed” to the accident. The service said, specifically, a solid undercast cloud layer from approximately 1,500 feet to 2,800 feet affected the recovery options of the pilot and radar controllers. The aircraft was completely destroyed and the Air Force values the total damage at $150 million.
Maintenance personnel have incorporated the investigation’s findings into multiple recurring inspections of the entire F-22 fleet that ensure aircraft are operating at acceptable risk levels. Officials are also planning a permanent modification to the parts separating hydraulic and electrical lines to further minimize the chance of a recurrence of a similar event, the Air Force said.
The pilot was originally the flight lead of a two-aircraft training sortie, or practice run, according to the AIB report. When the aircraft was approximately 35 nautical miles east of Tyndall AFB, at approximately 3:12 p.m. EST, the aircraft experienced a left generator failure that would not reset. The pilot began recovery procedures and directed his formation to split for separate instrument recoveries. During the pilot’s recovery, additional failures of critical and hydraulic systems required a left engine shutdown at 3:27 p.m. EST.
Approximately 90 seconds later, the aircraft displayed indications of a complete left hydraulic system failure. Thirteen seconds later, the aircraft’s right hydraulic system began to leak with indications of impending pressure failures. During the next three minutes, the pilot experienced difficulty controlling the aircraft along with significant and cascading flight control anomalies. The pilot began an immediate climb and noticed a large smoke train emanating from the aircraft’s mid-fuselage. At approximately 3:33 p.m. EST while heading south over Tyndall AFB, the aircraft began an uncommanded roll to the left in a nose low attitude. The pilot then initiated a successful ejection at approximately 3:33:22 p.m. EST and the aircraft impacted the ground nearly 12 seconds later, according to the report.
The pilot ejected safely, was recovered by Tyndall AFB emergency response members and sustained no significant injuries, according to an Air Force statement.
The Air Force said a previous F-22 crash at Tyndall AFB in May 2012 was caused by the pilot failing to advance power before initiating landing gear retraction (Defense Daily, Nov. 20).
The F-22 is developed by Lockheed Martin [LMT].