AIR accident investigators have concluded an aircraft involved in a fatal plane crash last summer was unfit for purpose saying key safety checks were not done.

RAF test pilot Flight Lieutenant Alexandre Jay Parr, of the Empire Test Pilots School (ETPS) at Boscombe Down, was killed when the Yak-52 he was flying came down in a Dinton field on July 8, 2016.

A civilian pilot acting as pilot in command was cut free from the wreckage with serious injuries and survived.

Concluding that the accident was caused by a failed forced landing attempt following an unexplained engine problem, the Air Accidents Investigation Branch (AAIB) said a range of issues had likely contributed to the crash.

It ruled that due diligence required to ensure a safe flight "fell short", adding there was inadequate supervision, a lack of risk assessment and poor reporting.

The privately-owned aircraft, contracted into MoD Boscombe Down by QinetiQ as a service from a third party supplier was being used as part of an annual Yak-52 training week for test pilot students, and had already completed a number of flights.

Investigators found that during their flights, students had noted "various unserviceabilities" with the aircraft but none were reported.

On the day Flt Lt Parr, an ETPS course tutor, was flying the aircraft as part of his own professional development. He had conducted aerobatic manoeuvres before the engine stopped forcing them to transmit Mayday calls at around 10.30am.

Investigators found the aircraft had launched with significant equipment defects - failed RPM gauges in both the front and rear cockpits, failed gyro compasses, an inoperative altimeter and a failed rear cockpit attitude indicator.

The report states: "These failures would have denied the accident crew critical information during the emergency and likely caused distraction and confusion."

It said the pilots' parachutes "appeared out of date", the seat harness straps were "significantly weakened" and that Flt Lt Parr had not worn a helmet.

And while investigators said the aircraft had been serviced, it had not had an engine overhaul in 24 years because it never reached the required 750 hours limit for one which "while legal was perhaps questionable".

Highlighting issues with the contract hire of the aircraft, it said QinetiQ had relied upon a sub-sub-contracted operator to ensure the aircraft remained safe throughout the week.

But the report states: "Overall, no stakeholder grasped the reality of a sub-sub-contractor operating a borrowed aeroplane or the implications that this introduced either in the context of unassessed risk or the chain of command's understanding of what was actually being delivered. In short, stakeholders assumed all was well but did not check the detail with qualified persons.

"This led directly to ETPS personnel flying in an aircraft that was unfit for purpose and operating in contravention of the Air Navigation Order."

The pilot in command was "inadequately prepared" for the training week, having only logged one flying hour in a Yak-52 in the previous year.

Investigators said: "It is reasonably believed that his lack of recent practice forced landings reduced his ability to carry out a successful forced landing on the day."

The report which notes the Yak-52 has been involved in 11 fatalities in the UK to date concludes: "Regardless of the inadequacies of the contract hire, what perhaps is even more surprising is that this [training] operation continued at ETPS for a week without either the aircrew, engineers or supervision picking up on what was clearly an unprofessional and deteriorating situation.

"We need to ask ourselves why this could happen under the gaze of the world's premier Test Pilot School."