On 30 August, ZK-NBS, the first Boeing B747-400 aircraft acquired by Air New Zealand, had a failure in the right hand, trailing edge, inboard fore-flap.
The failure was not immediately noticed by the crew, as the fore-flap retracted normally, there was no instrument indication of a fault, and no visible evidence of the detachment after the flaps had been retracted.
The first indication the crew had of a problem was when the flaps were being deployed to Los Angeles Airport. The crew could not get the desired landing flap setting, conducted a go around; and then selected a second setting and landed without incident. At the terminal the remains of the fore-flap were seen, together with other damage caused during the failure and subsequent operations of the flap.
At about the same time, a local fisherman on the Manukau harbour, discovered a piece of debris which was later determined to be part of the fore-flap assembly.
Operations staff immediately initiated disrupt procedures; engineering and safety staff started to mobilise and the Civil Aviation Authority and the Transport Accident Investigation Commission were advised of the incident.
Group Safety and ANZES established formal investigative teams, and the TAIC established its independent investigating team. Air New Zealand is co-operating fully with TAIC and keeping the Civil Aviation Authority fully informed.
A small ANZES team was despatched to Los Angeles to carry out inspection and repair on the aircraft, with assistance from United Airlines, one of our Star partners, and United Engineering.. They spent last week examining the aircraft, removing and providing the failed parts to the investigator from TAIC. The US National Transportation Safety Board acted on behalf of TAIC in the USA.
A portion of the fore-flap was still attached to the aircraft and there was significant damage to the mid-flap, and minor structure behind the wing. Minor damage to the fuselage and horizontal stabiliser was also found. A failed lug of a fore-flap link was found within the wing of the aircraft. This small piece of metal has proven to be a vital piece of evidence and was taken into custody of the NTSB for delivery to TAIC.
Even counting the portions found in the Manukau, there are still missing pieces despite extensive searching to date. It is becoming more and more likely that these will not be found. TAIC has advised us that it is satisfied that it has sufficient material to make a determination on causes, and further searching is not warranted.
Back in New Zealand, following the report of the incident, ANZES immediately conducted a visual inspection of the 747 fleet to ensure that there were no other immediate issues. Nothing untoward was found.
The ANZES team has reviewed all of the data surrounding the flap, and had discussions and data from Boeing.
The following relevant facts have been provided by Boeing:
* The world-wide 747 fleet has experienced previous fore-flap detachments, and several other operators have reported these events, with the last event reported last May * On the world-wide 747-400 fleet there have been 3 previous failures within the last 5 years that have been attributed to a failure of this very same link * Boeing advised that the lug failure would be the most likely cause of the detachment, and the consequent failures and missing parts had been seen on these earlier incidents * The link attachments are critical and carried all the fore-flap loads. Other failures appeared similar to ours. As a result of this data, ANZES quickly instituted an NDT (Non destructive test) inspection of the fleet, focussed on the lug that failed. As one aircraft was being prepared for the NDT test, signs of corrosion product staining were observed on one lug. While this did not indicate a failure was imminent, as a precaution, the lug was removed and replaced with one off a 744 that was in the hangar for a maintenance check. The replacement lug was checked and cleared as sound before installation in the aircraft being returned to service.
Probable causes of failure: ANZES management, in conjunction with the Air New Zealand Safety and ANZES investigation teams, then reviewed their findings to date. These findings are : * The configuration control and maintenance practices that are used in regard to the fore-flap assembly and components were fully compliant with the Boeing and NZ Civil Aviation Authority requirements * The probable causes of the lug failure were some initial movement in a bearing face, then some corrosion in a bearing face, followed by some stress cracking and then fatigue cracking leading to fracture. (All of this will be confirmed or added to once detailed metallurgical studies of the fracture face are completed)
Corrective actions: * At the next `A` check on ZK-NBS this weekend, ANZES will perform some sample inspections of the out-board fore-flap links, as a prudent precautionary step * ANZES will replace all the inboard lugs on the inboard fore-flaps on the 747-400 operating fleet during routine maintenance `A` checks. The parts have been obtained, and the fleet will have the new parts installed by the end of the month * This is also clearly a precautionary action, but given the possibility of a wider industry issue arising from this incident and subsequent pressure on spares, the company has acted prudently * ANZES will now work with Boeing to determine if any specific maintenance procedures should be introduced into the maintenance programme at Air New Zealand, or for the B747-400 fleet world-wide. These outcomes and actions have been fully endorsed by Senior Management, and have been communicated to the TAIC investigators.