Incidents involving misaligned nosewheels discovered to have four main causes
Investigators studying the landing in September by a JetBlue Airways Airbus A320 with a misaligned nosewheel have indicated that the aircraft had suffered damage to its shock-absorber assembly.
While the investigation remains open, the International Federation of Air Line Pilots’ Associations (IFALPA) says information from Airbus reveals that anti-rotation lugs in the upper support of the A320’s nose-gear shock absorber were damaged.
The A320 made an emergency landing at Los Angeles on 21 September with the nose-gear turned 90° to the runway centreline. Similar incidents involving Airbus narrowbodies, including a separate JetBlue A320 landing in November 2002, have involved a number of different causes for the misaligned wheels.
These have included incorrect installation of the nose-gear cylinder’s upper cam; in these cases anti-rotation lugs at the top of the shock absorber had not been seated properly following a maintenance visit. Investigators concluded that this was the reason behind the earlier JetBlue incident.
Citing a bulletin from Airbus, IFALPA says that the JetBlue A320 involved in the September landing had displayed “landing-gear shock absorber fault” and “nose-wheel steering fault” warnings to the flightcrew.
These warnings, says the association, do not necessarily mean the wheels are not centred, but indicate that such a situation is possible.
IFALPA adds that it has identified 13 similar incidents over the past 10 years, with four primary causes established. Aside from the incorrect reassembly of the nose-gear (attributed to three cases) there were five events linked to early versions of the brake and steering control unit.
Four events were traced to malfunctions of the hydraulic steering block caused by extruded seals, prompting a nosewheel rotation runaway, while the remaining incident was due to an under-performing shock-absorber allowing aerodynamic loads to disengage the centring cams as the gear retracted.
Although the US National Transportation Safety Board says the gear has been disassembled by landing-gear specialist Messier Services in Virginia, it adds that no final conclusions have been reached on the September incident involving JetBlue.
Airbus says it is confident of resolving the issues, but will not comment on specific details.
DAVID KAMINSK8I-MORROW/LONDON
Source: Flight International
