SEVERAL versions of the Boeing 737 aircraft may be susceptible to critical damage caused by incorrect maintenance procedures, according to US aircraft safety inspectors. The damage could cause pilots to lose control of their aircraft.
The 737 is the world’s most popular passenger jet. There are almost 5000 in service, and they dominate the fleets of low-cost airlines in Europe, the US and Australasia. The models causing concern are the 200, 300, 400 and 500-series 737s, which account for more than half the total number of 737s flying today.
There have been four incidents in the last five years caused by the same kind of damage. The problem has not led to a crash so far, but the US National Transportation Safety Board (NTSB), which investigates aircraft accidents and near misses, is concerned. There is a clear risk to passenger safety, says Lauren Peduzzi of the NTSB. The board is urging the US Federal Aviation Administration (FAA) to issue a directive requiring all airlines that operate the susceptible 737s to perform immediate maintenance checks. FAA directives automatically become mandatory in Europe, too.
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In all four cases the problem has been traced to corrosion in a component of the main landing gear, called the retract actuator beam (see Diagram), which pulls the wheels up after take-off. The broken beam can cause damage to nearby control cables. The latest case, which became public this month when the NTSB alert was issued, happened in August 2003 on an Aer Lingus flight from Amsterdam to Dublin, and the breakage caused damage to the control cables that operate the plane’s ailerons and air brakes.
Boeing engineers who examined the broken retract actuator beam concluded that it fractured because of corrosion brought on by particles of aluminium oxide embedded in it. This happened after the landing gear had been blasted with non-standard abrasive grit during an overhaul in 1998. After the incident, the Irish Aviation Authority directed Aer Lingus and Ryanair to perform immediate checks on their fleet.
A similar case of beam breakage and cable damage following corrosion caused by over-enthusiastic cleaning of the landing gear occurred in Australia in 1999. Boeing issued a service bulletin describing the hazard in early 2003, but the NTSB is becoming alarmed that the FAA has not mandated checks on all appropriate 737 undercarriage mechanisms. The FAA will issue a ruling within the next three months.
