Chafed electrical wires in fuel tank conduits were found in so many older Boeing 737s that the US Federal Aviation Administration grounded many of them by issuing an emergency airworthiness directive (AD) on 10 May.

Checks on fuel tank pump wiring following an earlier AD had revealed that seriously chafed fuel tank wiring bundles existed in about 15% of inspected 737s which had flown more than 40,000h. Wiring was exposed in nine aircraft with over 50,000h.

All 737s with more than 50,000h were required to be grounded until inspection and rectification was complete, while in aircraft with more than 40,000h rectification within 14 days was demanded. On 14 May another AD lowered the inspection requirement to 30,000h for -100 and -200 models, and required a second layer of Teflon coating to be applied to wires.

Meanwhile, tests have continued on a damaged wiring conduit found on a Continental Airlines 737 (Flight International, 13-19 May). The investigation continues to suggest electrical arcing was the cause of pin-size holes found in the unit.

The 737 models affected are all those from the -100 to the -500, more than 600 aircraft in total.

Source: Flight International