A TOP Irish Air Corps flight instructor crashed into a mountainside with his trainee cadet after suffering an illusion, an investigation has found.
Captain Derek Furniss, 32, and Cadet David Jevens, 22, died when their two-seater light aircraft went down in Connemara's remote Crumlin Valley in October 2009.
Air accident investigators believe Capt Furniss - one of the military's most experienced teachers - succumbed to an airborne phenomenon known as somatogravic illusion.
The condition meant he believed their small Pilatus PC-9M plane was climbing steeply away from a mountain that unexpectedly appeared ahead when the plane was actually starting to nose-dive into it.
His last words, captured on the black box flight recorder 26 seconds before impact, were: "Bad decision now."
Overwhelming sensations caused by disorientation and confusion as bad weather closed in on them probably caused the pilot to disbelieve his instruments and steer the aircraft into a peak known as Maum Dearg, near Cornamona village, it was found.
Capt Furniss, from Rathfarnham, Dublin, and Cadet Jevens, from Glynn, Co Wexford, were on a cross country low-flying exercise with two other planes from Casement Aerodrome, near Dublin, to Galway and back.
A final report into the crash by the Air Accident Investigation Unit (AAIU) found that continuing the route in deteriorating weather, without reducing speed and in reduced visibility, contributed to the crash.
The flight also broke minimum height restrictions in the moments leading up to the impact.
Mr Jevens, in the front seat, had made a decision to bypass the mountainous valley because of the conditions but was directed by Capt Furniss to continue in and "look at our options when we get in a bit further".
Capt Furniss then directed a new, unplanned route be taken through through nearby Finny Valley.
But he quickly became concerned and abandoned the plan - probably because of the weather - and ordered his cadet to veer back to the old route "without reassessing the situation".
It is believed he took control of the plane briefly before handing it back to the trainee.
Investigators said there was a breakdown in understanding between the two at this stage as events happened faster and Capt Furniss became increasingly involved in handling the aircraft.
Cadet Jevens was ordered not to climb but to maintain ground contact, while the instructor seemed to progressively lose perspective of his whereabouts, it was found.
They crossed a rising ridge at one stage just 436ft above ground. The minimum height allowed for the exercise was 1,000ft, while the legal minimum is 500ft.
Capt Furniss seized control again as they headed at 1,400ft towards a 1,500ft mountain and when it came into view, he made a sharp turn before making his last remarks.
The investigation found the speed of final events amid mounting stress and anxiety were so quick that neither crew member had time to activate the ejection seats.
The AAIU said the accident had been classified as an "unrecognised disorientation" as the instructor only became aware of the true state of affairs at a time when the accident was inevitable.
The investigation also found there was no visibility report completed in the risk assessment form filled out before the training exercise.
There was no technical fault found with the aircraft.
The AAIU said the officer commanding of the Air Corps flight training school was not qualified to fly the military's eight Pilatus PC-9M planes, used as training craft for cadets.
This situation was not conducive to best practice for supervisory oversight, it said.
They made a number of recommendations, including a review on training for disorientation, qualifications of the officer commanding and regulations allowing flight instructors to authorise themselves.
The Defence Forces said it fully accepted the report's findings and would implement all the recommendations.
Defence Forces Chief of Staff Lieutenant General Sean McCann said: "I would like to extend my deepest sympathy to the families of Capt Derek Furniss and Cadet David Jevens on the tragic loss of their loved ones. I fully appreciate that the passage of time will not have dulled their absolute sense of loss."
Mr Jevens was due to graduate with Military Pilot Wings and Officer Commission.