Pilot error and faulty maintenance procedures have been blamed for the 2008 crash of an Air New Zealand plane that killed seven people off the coast of France.
New Zealand accident investigators have welcomed a French report into the crash, saying it identified key safety issues and lessons to be learned.
The Airbus A320 plunged into the sea off France's Mediterranean coast on November 27, 2008, killing five New Zealanders and two Germans who were conducting a low speed, low altitude test after a technical overhaul.
In its final report released today, France's BEA air accident investigation agency blamed the crash on maintenance errors and the pilots undertaking risky manoeuvres during an ad hoc test flight.
The pilots were not competent to fly at such a low level and ground crew had incorrectly washed the airliner, causing water to enter key detectors, the report found.
Air NZ chief executive Rob Fyfe said the airline supported the report's safety recommendations.
"While this report will not change the fact seven families lost dads, husbands, brothers and sons and we lost great colleagues, the findings will benefit the entire aviation industry."
New Zealand's Transport Accident Investigation Commission (TAIC), which assisted with the investigation, welcomed the report.
"The BEA's report has identified the key safety issues and lessons to be learnt from this complex accident, and made worthwhile recommendations to help prevent a similar accident in the future," TAIC chief investigator Tim Burfoot said.
The report noted that the journey was not a test flight, legally speaking, as it did not fall under the rules for commercial flights with passengers or official test flights.
Rather, the flight was an ad hoc run-out, which might have led the pilots to improvise rather than follow pre-assigned procedures.
Air traffic control had refused the crew's request to perform test manoeuvres because the flight plan did not include them.
The crew then adapted its programme of checks "in an improvised manner according to the constraints imposed by the flight plan and the air traffic control services".
While the German pilots were permitted to conduct the checks, they "did not have the training, experience and methods required to perform the flight programme".
An Air New Zealand pilot present in the cockpit "participated in an active manner in following the programme of checks".
The decision to undertake the test at a low altitude and at low speed contributed to the pilot's losing control of the plane, the report found.
It also criticised French maintenance firm EAS Industries, which had painted and cleaned the aircraft three days before its fatal final flight.
The firm's rinse of the aircraft "had not followed the proper procedures", allowing water to penetrate key instruments.
Once in flight, the water froze in the probes, which measure the plane's angle of flight and ought to have emitted a warning if the jet was stalling.
The instruments themselves were not to blame for the failure, but the report nevertheless recommended the development of new testing procedures to monitor the quality of on-board flight data monitoring.
It also recommended that stricter rules be drawn up for special flights like the one that led to the tragedy, which do not fall under the rules for commercial flights with passengers or official test flights
The report also recommended improved training exercises and techniques relating to low-speed flights.
Mr Burfoot today said the report's value to international aviation extended beyond its key findings and recommendations.
"It contains useful material to inform business-as-usual safety related planning and activity.
"This value includes in areas like regulatory oversight, aircraft leasing, test flight planning and conduct, crew training, maintenance, and component and system design."
A TAIC representative contributed to the investigation and received assistance from two Air New Zealand experts, the Airline Pilot's Association and the air force, Mr Burfoot said.
The plane, which had been leased to Germany's XL Airlines, had been flown to France for tests at the aerodrome in Perpignan and to be repainted before its return to the Air New Zealand fleet.
The New Zealanders killed in the crash were Air New Zealand pilot Brian Horrell, 52, Air New Zealand engineers Murray White, 37, Michael Gyles, 49, and Noel Marsh, 35, and Civil Aviation Authority official Jeremy Cook, 58.
All seven bodies were recovered from the crash scene.
The findings follow an initial decision by French prosecutors in June to not press charges over the crash.
"The BEA report will be entered as evidence in the procedure being carried out by two investigating judges in charge of the manslaughter inquiry. It will be studied," said Perpignan prosecutor Jean-Pierre Dreno.
The investigating judges have come to broadly the same conclusions as the BEA as to the cause of the crash.
Air New Zealand said it would review the report in detail and might make further comment later today.
The families of the New Zealanders killed in the accident have asked for privacy.
