The investigation into the crash on 19 December, 1997, of the SilkAir Boeing 737-300 is raising questions about why the aircraft's cockpit voice recorder (CVR) and flight data recorder (FDR) both stopped operating in quick succession just before the aircraft entered its steep, fatal descent.
Analysis of the CVR and FDR in Washington by the US National Transportation Safety Board has not yielded any useful information on a crash cause. The accident killed 104 passengers and crew. Indonesian investigators are trying to reconstruct the 737 from the 55% of the wreckage recovered from the Sumatran river where it crashed.
The CVR stopped 60s before the last radio transmission, a routine position report by the co-pilot, recorded by air traffic control (ATC). The FDR is believed to have stopped shortly after that, with no abnormal flight parameters recorded.
Industry observers suggest that the likelihood of the CVR and FDR failing in quick succession is remote. They have indicated that simultaneous failures have been known, but these were associated with explosion, catastrophic failure, or multiple engine failure. An employee of the Singapore Airlines group, of which SilkAir is a member company, says that the 737's engines were operating during the descent.
The only remaining plausible theory is manual de-activation of both systems. The CVR and FDR can be switched off from the cockpit by pulling their respective system's circuit-breaker (C-B), although the motivation for such an action is puzzling. The C-B panel is directly behind the co-pilot's seat and neither the pilot nor the co-pilot would necessarily be aware the breakers had been pulled without inspecting the panel.
In reply to whether deliberate crew action to disable the flight recorders was within the scope of the investigation, Professor Oetarjo Diran, head of the Indonesian investigating team told Flight International: "You said it, it's a theory, let's call it a theory right now and then we are going to prove or disprove that theory."
Source: Flight International
