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Crash landing pilots ignored warnings


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

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