Two leaked internal documents contradict claims by the Ministry of
Defence that problems with the engine control system of the Chinook
helicopter that crashed on the Mull of Kintyre in 1994 could not
have endangered the aircraft.
Tony CollinsThe documents also raise new questions about whether ministers,
briefed by officials, have inadvertently misled Parliament over the
crash. The documents are likely to be discussed in the House of
Lords next Monday.
Peers are due to vote on a motion, put forward by former Labour
foreign affairs minister Lord Chalfont, for a select committee to
investigate the Chinook crash. If the motion is passed, it will be
the first time in recent years that the Lords has formed a select
committee.
The crash killed four crew and 25 senior police and intelligence
officers. An RAF Board of Inquiry found insufficient evidence to
blame the pilots. But an air marshal, supported by his superior,
disputed the findings and ruled that there was absolutely no doubt
whatsoever that the pilots were grossly negligent. This was in
effect the final ruling.
One of two leaked MoD Air Publications referred to a Block One
upgrade to the Chinook's Full Authority Digital Control (Fadec)
system which was introduced in late 1994 - several months after the
crash - to address nine software anomalies.
One of the changes, said the document, was to address the
problem of pilots encountering an engine acceleration without their
command when the Fadec was in "reversionary mode", a back-up to the
system's primary mode.
Another of the changes was designed to deal with the opposite
problem of "uncommanded engine shutdown in reversionary".
A Fadec's hydromechanical unit was found in reversionary mode on
the crashed Chinook, but this was said to have been a normal
consequence of fuel shutdown at or after impact.
In a Parliamentary reply to MP Desmond Swayne in August 1999,
armed forces minister John Spellar listed details of the nine Block
One software changes without making any mention of uncommanded
engine acceleration or shutdown. Spellar said the Block One upgrade
was part of a "product improvement programme".
He said one of the software changes addressed an "error" which
occurred when "switching to the reversionary system during
pre-flight ground checks". Another change was the fitting of a
"software filter" to "reduce the number of incorrect computer
computations experienced at very low speeds during engine start
up".
In a statement to the Public Accounts Committee, published in
November last year, the MoD said of the Block One update that it
addressed "nuisance faults".
The second leaked document, dated 1997, said that an erroneous
signal to the Fadec may limit the engine power available when
maximum power is needed or only one of the two engines is
running.
The MoD said the problems highlighted by the leaked documents
were "unlikely" to affect safety.
tony.collins@rbi.co.uk