Findings in an inquiry into an Air Nelson plane that skidded along a runway on its nose landing gear doors have been dismissed by the airline, which says the incident was due to inaccurate advice from the plane's manufacturer rather than the pilots.
The Transport Accident Investigation Commission (TAIC) has found the pilots of a Bombardier Dash 8 ignored two warnings that the landing gear was unsafe as it came in to land at Blenheim on September 30, 2010.
None of the three crew or 43 passengers were injured and the plane suffered minimal damage.
The flight had been travelling to Nelson from Wellington but was diverted to Blenheim because of poor weather.
As the two pilots prepared to land, the nose landing gear stopped before it had fully extended, probably because debris within the hydraulic fluid blocked a small opening that worked the nose landing gear, the TAIC report said.
A warning system indicated to the pilots the landing gear was "unsafe'', that the nose landing gear was not down and locked, and that the nose landing gear forward doors were open.
However, a second independent system showed the pilots that all the landing gear was down and locked in spite of the other indications that it was not.
The pilots assumed there was a fault in one of the landing gear sensors and continued the approach to land expecting that all the landing gear was locked down.
On the final approach the landing gear warning horn sounded to alert the pilots that the landing gear was not safe.
However, the pilots ignored both of these warnings in the belief they had been generated from a single sensor that they assumed was faulty and had given them the original unsafe nose landing gear indications.
When the plane touched down the nose landing gear was pushed into the wheel well and the aeroplane completed the landing roll skidding on the nose landing gear doors.
Air Nelson flight operations manager Captain Darin Stringer today said the airline fundamentally disagreed with some of the TAIC findings and its pilots had been following protocols.
"Those protocols are based on information from the manufacturer, Bombardier, that has since been found to be inaccurate.
"At the core of this incident is clear advice from the manufacturer which indicated that three green lights from either the primary or secondary landing gear systems was absolute confirmation that the gear was in place and safe.''
Mr Stringer said the airline had now stipulated that, should a similar situation occur in future, a visual inspection must be made by suitably qualified ground observers.
He added the pilot did not ignore the aural warning system, and had expected to hear it on approach because there was a known fault.
"The pilots expected the warning and proceeded to land in line with the protocols set out by the manufacturer.''
TAIC lead investigator Peter Williams said the actions of the pilots were "understandable'' in terms of the information they had.
He said the pilots could have asked someone from the ground to have a look at their undercarriage to say what was happening with the nose wheel.
"The most important thing in this case was to have accepted the other warnings they got towards the end, the oral warnings, and rather than rationalising why they were occurring and flown the circuit again and asked someone outside to see what it looked like.''
If the pilots were still unable to unblock the debris from the landing gear, the pilots would have still needed to land the plane, Mr Williams said.
"The only difference is they would have known the nose gear wasn't down and they could have been a bit better prepared. But the outcome would have been the same.''
Air Nelson, which is a subsidiary of Air New Zealand, and the Canadian aeroplane manufacturer, Bombardier, took a number of safety actions to address issues raised by the TAIC.
The commission also recommended to the Director of the New Zealand Civil Aviation Authority to work with Canadian authorities to require the manufacturer to improve the reliability of the landing gear verification system.