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ONE of the two black boxes which would have held major clues to the cause of last month's Hercules crash at Kai Tak airport was not working properly and the other was so old it was of limited value, says an interim report into the accident.

  The cockpit voice recorder was found to have only been working intermittently and contained no information on the cause of the crash in which six people died.

  The flight data recorder was an old scratch-foil type which gave only limited information to accident investigators concerning the plane's heading and speed.

  There was also no quick access recorder, which many planes now carry to provide constant updates of instrument and component performance and can be used for initial stages of investigations.

  A spokesman for the Air Accidents Investigation Branch in London, which sent two investigators to Hong Kong after the crash on September 23, said the investigation would suffer as a result.

  Sources said the black boxes usually form part of the pre-flight checks and should also be examined during routine maintenance.

  But it appears the crew was unaware of the fault in the cockpit voice recorder.

  There is no requirement for older aircraft to be fitted with sophisticated computerised flight data recorders which are now available. However, the scratch-foil type records only very basic information.

  'The modern recorders can record more than 100 parameters and then be put through a computer to build up a picture of the flight,' an aviation source said.

  'The scratch-foil ones are literally a needle which scratches a piece of foil and can only record a few parameters such as speed, heading, pitch and roll.'   International Civil Airline Organisation regulations state that all commercial aeroplanes must be fitted with black boxes, but older ones originally fitted with the scratch-foil type do not have to be updated.

  The South China Morning Post has revealed that investigators believe the accident was caused by pitch-lock in the number four propeller just after take-off.

  Pitch-lock, which usually only occurs in the event of control failure, locked the angle of the propeller blades and pushed the aircraft into a right-hand dive due to uneven thrust.

  But the lack of information from the voice recorder means vital pieces of corroborating evidence are missing and the flight data recorder could not record information from the propellers or engines.

  No one from Pelita Air Services, the Indonesian owners of the 15-year-old aircraft chartered by the Hong Kong Government for refugee repatriation flights to Vietnam, was available for comment yesterday.

  The preliminary accident bulletin, issued by law by the Civil Aviation Department to concerned parties, said the initiating event which caused the accident appeared to be a problem with the number four power unit.

  All four propellers and the number four engine have been sent to their respective manufacturers for detailed examination.

  The report said Soeyono Sanarphi, the 40-year-old pilot who was plucked from the harbour with other injured members of his crew, told the investigation team that all pre-flight checks and the take-off were normal.

  Seconds after the plane left the runway, as the co-pilot was reaching for the lever to raise the landing gear, Captain Sanarphi heard a high-pitched noise coming from his right.

  He then struggled with the controls to counter a pull to the right by applying left rudder and full left aileron.

  'The aircraft continued its turn to the right and buffeting set in as if in a stall,' the report said.

  '(The pilot) then brought number one throttle back in an attempt to stop the turn but that has no effect.

  'The aircraft hit the water nose and right wing first and quickly sank below the surface,' the report said.

  The plane was on its way to Jakarta with 12 crew on board.

  The only survivor still in Hong Kong, Joseph Hermanus Tepilatu, was in a fair condition last night in Queen Elizabeth Hospital.



Faulty black box hits Hercules crash probe