What happened
On 18 October 2008, a Hawker Hunter F6.A, registration G-KAXF, was conducting a private general handling flight departing from Exeter Airport. Upon touchdown on Runway 2CL, an external fuel tank detached from the left wing of the aircraft. The tank, which contained roughly two gallons of fuel, landed on the grass south of the runway, where it struck a runway edge light and caused damage to the runway surface.
The pilot had selected the landing gear up following the landing and, despite a cockpit indication suggesting the nosewheel door had not locked, continued to taxi normally. The pilot was unaware of the detached tank until notified by the aerodrome controller. Following the incident, a portion of the runway was closed for 30 minutes to allow for damage assessment.
The investigation
The AAIB examined the mechanism responsible for securing the tank, which was an electromagnetic tank release unit. This unit utilized jaws that closed around a lug on the tank. The investigation established that the physical force exerted on the jaws by the tank during the landing impact was sufficient to trigger the release.
It was noted that the aircraft was operating under a Permit-to-Fly, and the specific release unit configuration lacked a modification used on Swiss-registered Hunters. That modification employs clamps to prevent the jaws from opening inadvertently. The investigation found no evidence that the release unit was unserviceable prior to the event.
Findings
- The primary cause of the tank detachment was the impact force of the landing acting upon the electromagnetic release unit jaws.
- The 150-gallon drop tank was held by an electromagnetic unit that lacked the mechanical clamps found on Swiss-registered aircraft, which are designed to prevent accidental release.
- The pilot did not perceive the landing as being particularly heavy.