What happened
On 16 June 2021, a P84 Jet Provost Mk 5, registration G-VIVM, was performing a post-maintenance check flight at North Weald Airport. During the initial takeoff roll, the pilot noted that the airspeed indicator (ASI) failed to provide any reading. This prompted a rejected takeoff (RTO), during which the aircraft was brought to a halt and returned to the maintenance area for inspection.
Following a period of maintenance and a successful verification of the pitot/static system by ground staff, a second takeoff attempt was initiated. During this second roll, the pilot again observed no movement on the ASI. The pilot decided to abort the takeoff at an estimated speed of 70–8 and0 kt. Despite the application of heavy braking, the aircraft failed to stop before the end of the paved surface. The aircraft exited the runway, entered a grassy area, and eventually came to rest after striking an earth bank and the airport perimeter fence. There were no injuries to the two occupants, though the aircraft sustained significant damage to the nose structure and main landing gear.
The investigation
The AAIB investigation focused on the cause of the airspeed indicator failure and the subsequent failure of the braking system to stop the aircraft. Technical examinations of the pitot/static system and the ASI itself, conducted with the involvement of a CAA Airworthiness Surveyor, found no defects or blockages. The ASI was found to be within calibration limits and responded correctly to pressure tests.
Regarding the braking system, investigators examined the wheels and brakes in-situ and at AAIB facilities. While the aircraft lacked an anti-skid system, the tyres showed no signs of flat spotting, indicating the wheels continued to rotate during the RTO. However, the investigation found significant heat-related damage to the brake discs and calipers. Notably, the floating friction pads had been displaced from their pistons, with some even found detached from the assembly. This displacement, combined with metal-to-metal contact between the piston crowns and the discs, likely compromised the efficiency of the brakes during the high-energy deceleration.
Findings
- The specific reason for the lack of airspeed indication on the ASI could not be determined.
- During the second takeoff attempt, the aircraft reached a groundspeed of approximately 105 kt, which was higher than the pilot's estimate.
- The braking demand during the rejected takeoff exceeded the available braking capability of the aircraft within the remaining runway distance.
- The displacement of the floating friction pads during the high-speed braking event likely reduced the overall braking efficiency.