The Hawker Hunter which was involved in a fatal air display accident in the UK on 22 August had no reported defects prior to taking off, and appears to have been performing as expected prior to the crash, the Air Accidents Investigation Branch (AAIB) says.

Releasing preliminary information about the accident in a Special Bulletin on 4 September, the AAIB says that information recovered from two cameras installed inside the vintage jet’s cockpit indicate that “Throughout the flight, the aircraft appeared to be responding to the pilot’s control inputs.” Eleven people were killed and the pilot seriously injured when privately-owned G-BXFI crashed onto a busy road next to Brighton City airport during the Shoreham air show.

An inspection of the 1955-built Hunter performed at its home base at North Weald in Essex the previous afternoon shows “no reported defects”. The aircraft and its under-wing external tanks were fully fuelled prior to a take-off run which the AIIB notes was “longer than usual”, probably due to a high ambient temperature and a tail-wind of around 8kt (15km/h).

Conditions at the time of accident were recorded as a 12kt wind across the display airfield and an ambient temperature of 24˚C, “with no significant cloud and visibility of more than 10km”.

After starting the display, the Hunter was “pitched up into a manoeuvre with both a vertical component and roll to the left, becoming almost fully inverted at the apex of the manoeuvre at a height of approximately 2,600ft,” the bulletin says. The latter reading was captured by Heathrow radar, although the AAIB notes that the figure “may not reflect the peak altitude achieved because the radar data was not continuous.” The aircraft appears to have slowed to an indicated airspeed of approximately 100kt, it adds.

“During the descent the aircraft accelerated and the nose was raised, but the aircraft did not achieve level flight before it struck the westbound carriageway of the A27,” the AAIB says. “Ground marks and photographic evidence show that the aircraft struck the road in a nose-high attitude,” with the first contact “made by the lower portion of the jetpipe fairing.”

Following this, “fuel and fuel vapour from the fuel tanks was released and then ignited. The aircraft broke into four main pieces, which came to rest close together approximately 243m from the initial ground contact.” The 11 fatalities occurred when the aircraft “struck vehicles and persons around the road junction,” it says.

“During the initial part of the impact sequence the jettisonable aircraft canopy was released,” the bulletin confirms, with this shortly followed by the pilot and his seat being thrown clear from the cockpit section. “The investigation continues, to determine if the pilot attempted to initiate ejection, or if the canopy and pilot’s seat were liberated as a result of the impact damage to the cockpit,” it adds.

The main sections of aircraft wreckage have been taken to the AAIB’s facilities in Farnborough, Hampshire, while smaller items are still being recovered from the crash site.

According to its investigation, the pilot – who was described as “being in good spirits and looking forward to the flight”, held a full Class 1 medical certificate, and a valid display authorisation from the UK Civil Aviation Authority to fly the Hunter to a minimum height of 500ft “during standard category aerobatic manoeuvres”. He had accumulated just over 40 flying hours on the ex-military type since May 2011, including almost 10h within the 90 days before the crash and 2h in the four weeks before the mishap.

The AAIB says its bulletin was compiled using “preliminary information gathered from ground inspection, radar data, recorded images and other sources”. Its work is continuing its work, with further investigation to “examine the aircraft and its maintenance records, explore operation of the aircraft, the organisation of the event with regard to public safety, and associated regulatory issues.”