SAS MD-81 crash report, December 1991

From:         Martyn Thomas <mct@praxis.co.uk>
Date:         15 Nov 93 12:23:27 PST
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According to Flight International, 10 NOVEMBER 1993, "an automatic
engine-control function in the McDonnell Douglas MD-81, of which the
operating airline was unaware, was a major factor in the Scandinavian
Airlines System (SAS) accident near Stockholm, Sweden, in December 1991,
says the official report into the accident"

In summary, it seems that the airline failed to detect clear ice on the
wings before takeoff. The ice broke free and entered the engines damaging the
fan stages. This caused the right engine to surge. The pilots retarded the
right throttle. The automatic thrust-restoration system ATR caused both
throttles to advance without the pilots noticing, making the surging worse
in the right engine and starting surging in the left. The surges destroyed
the engines.

It seems that SAS were unaware of the ATR, which was documented but in a
section of the production flight-procedure manual dealing with noise
abatement. SAS VP Johan Juhlin is reported as saying "We did not order it.
It was hidden in the computer. The only way to disconnect the ATR was to
disconnect the whole autothrottle system."

McDonnell Douglas say that they made SAS aware of the full capabilities of
the MD-80 when it was delivered.

The documentation has since been improved, and SAS have changed their
procedures and training to emphasise the ATR and correct anti-surging
procedures.

The ATR was designed to improve safety where an engine fails after take off
and noise abatement procedures have caused the engines to be throttled
back.
-- 
		      These are personal opinions only
      Martyn Thomas, Praxis plc, 20 Manvers Street, Bath BA1 1PX UK.
Tel:	+44-225-444700.   Email:   mct@praxis.co.uk 	Fax: +44-225-465205