Turbulent weather has emerged as a possible factor in the SilkAir Boeing 737-300 accident, about which there has been, so far, no statement by the Indonesian investigating authorities. The aircraft disappeared from cruising flight near Palembang, Sumatra, on 19 December on a scheduled flight from Djakarta, Indonesia, to Singapore. All 104 people on board died.
The crew of Qantas flight QF41, a Boeing 747SP flying 5min behind the SilkAir flight (MI185) at 41,000ft (12,500m) on the same route, asked for a diversion around bad weather, as did crews of at least three other aircraft. The weather, however, was not enough to bring down a 737, sources say, unless it had an impact on structural weaknesses in the aircraft.
The first officer had been logged as the pilot flying for that sector, and air-traffic-control tapes indicate that he made the last, procedural, radio transmission.
The cockpit-voice recorder does not record the last 60s of the flight, and the last 30s of the flight-data recorder information is damaged, according to the US National Transportation Safety Board, tasked with reading the tapes.
Meanwhile, the airline is denying rumours that a crane had earlier collapsed on the 737's tail and that the resulting damage took three or four days to repair. The 737 had undergone a maintenance C-check shortly before the accident.
On 8 January, the US Federal Aviation Administration required operators of 211 Boeing 737s delivered after 30 September, 1995, to check the horizontal stabilisers for missing fasteners and elevator-attachment fitting bolts. The precautionary measure followed the discovery that 26 fasteners on the horizontal stabiliser and one bolt from an elevator attachment may have been missing from the SilkAir 737 before impact.
Incidents of severe elevator-tab vibration following the loss of fasteners have been known to occur on earlier 737-200s. Maersk Air and China Airlines have reported tab-vibration which, in the latter case, caused horizontal-stabiliser cracking almost to the leading edge.
All 737s up to the -500 models are to have their yaw-damper-coupler internal rate-gyroscopes replaced, an FAA airworthiness directive (AD), effective on 17 February, states. The AD, a by-product of the critical design review of 737 rudder-control systems following loss-of-control accidents involving United Airlines in 1991 and USAir in 1994, is intended "to prevent sudden uncommanded yawing of the aeroplane due to potential failures within the yaw-damper system".
Source: Flight International
