Wing-flap fall blamed on design

The loss of a wing part on an Air New Zealand jumbo jet last year was caused by a stress fracture, an investigation has concluded.

Flight NZ2, with 355 passengers and 17 crew aboard, lost a 2m section of wing flap over Manukau Harbour shortly after takeoff from Auckland International Airport on August 30.

According to the report by the Transport Accident Investigation Commission released today, the crew was unaware of the problem until the landing approach at Los Angeles 12 hours later, when the pilot had difficulty extending the flaps.

It was the second incident within a week of an Air New Zealand jet losing a wing segment over Auckland during a time when problems dogged the airline.

The TAIC report into the August 30 incident said about 70 per cent of a wing flap ripped off shortly after takeoff. Slight bumps felt by crew and passengers were put down to turbulence.

But when the captain went to land at Los Angeles, the flap failed to select.

After one aborted approach, and discussion between the flight crew and an off-duty pilot on board, the plane landed normally using a different landing sequence but at a higher than usual speed.

Part of the flap was still attached to the aircraft but skewed 20 degrees.

The missing piece was recovered by the crew of a fishing boat in Manukau Harbour at about the same time NZ2 landed at Los Angeles.

Investigators concluded a design fault was to blame for the incident, in which a link attachment bolt failed because of corrosion.

Metallurgical tests on the recovered wreckage concluded it was "highly unlikely" that incorrect installation or use of the material caused the failure.

The metallurgist said the aluminium alloy used to manufacture the link was prone to stress corrosion cracking and such failures were not unknown.

The crack had probably grown quickly over just a few flights, and routine maintenance would not have picked it up.

There had been three such fractures reported worldwide since June 1997, spurring Boeing to initiate a design improvement programme in June 2002 to enhance the corrosion resistance.

This should provide a long-term solution, the report said.

Air NZ operations and technical senior vice-president Craig Sinclair said none of their planes had modification as part of the Boeing review, either before or after the incident.

They had all been subject to internal inspections.

Mechanical failures

May 9, 2001: A Boeing 767 loses a piece of "wing flap track guide", which fell through a warehouse roof in South Auckland.

August 24, 2001: A Boeing 747 loses a pylon inspection panel from the upper wing surface during the plane's departure from Auckland, en route to Japan.

August 30, 2002: A 747 lost a "trailing edge inboard fore-flap" departing from Auckland for LA.

September 25, 2002: A controlled shutdown of one of four Rolls-Royce engines on a 747 due to high temperature. The London-LA flight turned back and landed safely.

December 8, 2002: A General Electric engine on a 767 failed when a fatigue-cracked turbine disc punched a hole in the engine casing and damaged the wing.