A training exercise involving a helicopter at an Essex airfield led to a "serious incident", a report has said.

The pilot of a MBB-BK 117 helicopter was forced to make a "firm landing" during an exercise at North Weald airfield in Essex on March 12 last year.

The Air Accident Investigations Branch (AAIB) said it occurred during a demonstration of an engine failure after take-off when throttle was reduced in one engine to simulate a failure.

The commander attempted to increase the throttle but the engine did not respond, while throttle "inadvertently" reduced in the second engine.

The report said this "probably resulted from the commander’s hand accidentally overlapping its throttle" as he tried to increase engine one.

An engineering investigation did not find any evidence of malfunction in the engine control systems.

Because of the engine failure, the pilot rejected take-off while 19ft above ground level and decided to land.

The AAIB said this landing was "firm", leaving skid marks on the airfield and causing "significant" damage to the landing gear.

There were no injuries reported but the AAIB described it as a “serious incident”.

The AAIB said the pilot had been taking part in the exercise at the airfield to revalidate his instructor qualification and an examiner was present.

Investigators at the AAIB said the incident “reinforces the benefit of using flight simulators wherever possible to de-risk training”; however the AAIB said the incident “could possibly have been avoided” by using a different throttle handling technique when simulating the engine failure.

The AAIB said the operator had tried to organise flight simulator training but no suitable options were found.

The airfield now provides simulator-based training for scenarios involving one engine.

While the AAIB investigation was still ongoing, the operator opted to only carry out similar-type training with both engines at flight.

The report into this incident was published on the AAIB website on February 3.