Precautionary checks on certain Boeing 737-300s, -400s and -500s have been ordered by the US Federal Aviation Administration following the discovery of tailplane wreckage from the crashed Silk Air 737-300. Fasteners are missing from sections of the horizontal stabiliser, and bolts from elevator attachments.

The accident occurred on 19 December when the aircraft, with no emergency call from the crew, dived from its 35,000ft (10,700m) cruising height into the Musi River, Sumatra en route from Djakarta, Indonesia to Singapore.

The checks for each aircraft take about an hour. Silk Air, having completed the work on its five 737s, says that no fasteners or bolts were found to be missing, and it is confident that its normal line-checks would have discovered the absence of any such components.

All 737s delivered after 20 September, 1995, are affected by an airworthiness directive (AD) issued on 8 January. Some 213 aircraft are involved. By 9 January, the FAA says, it had been notified of one loose fastener.

The FAA stresses the precautionary nature of the AD. Investigators looking for evidence at the crash site say that almost all the wreckage is in extremely small pieces. One theory is that any missing fasteners could have detached during the dive or at impact.

The flight-data recorder was found on 27 December, 1997, and the cockpit voice-recorder on 4 January, but their contents have yet to be revealed. Silk Air has discounted rumours about damage to the rear pressure-bulkhead, and Lloyds Aviation of London says that there is no record of any damage to the airframe which would have affected the bulkhead.

A row of three seats was found 10km (5nm) from the main impact position. It is unclear whether this could imply airframe break-up before impact, but secondary radar traces have revealed a maximum 22,000ft/min (111.76m/s) rate-of-descent - 2.5 times the 737's maximum emergency-descent rate.

Source: Flight International