A plane carrying 46 people skidded along a runway on its nose landing gear doors because the plane's pilots ignored two warnings that the landing gear was unsafe, an inquiry into the incident has found.
None of the three crew or passengers were injured and the Dash 8 suffered minimal damage during the incident on September 30, 2010, the Transport Accident Investigation Commission inquiry said.
The Air Nelson flight had been travelling to Nelson from Wellington but was diverted to Blenheim because of poor weather.
When the two pilots moved the landing gear selector lever to down, the left and right main landing gear legs extended normally but 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 that 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.
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 Limited and the Canadian aeroplane manufacturer, Bombardier, took a number of safety actions to address issues raised in the TAIC's report.
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.
Key lessons arising from this inquiry were:
* when critical systems begin intermittently to malfunction or behave abnormally, this is often a precursor to total failure;
* the more a pilot knows about aircraft systems, the better armed they will be to deal with emergency and abnormal situations'
* aircraft warning systems are designed to alert pilots to abnormal conditions. Alerts should not be dismissed without considering all other available information; and
* pilots must retain sufficient knowledge of aircraft systems to deal with situations not anticipated by Quick Reference Handbooks.
- Rebecca Quilliam of APNZ
