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Output Number
IR19990076
Approval Date
Published Date Time
Recommendation type
Interim recommendation
Mode
Aviation
Date released

The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority examine the circumstances surrounding
this occurrence and take whatever steps it considers necessary to
ensure the safety of the Saab 340 fleet operating within
Australia.



As a result of the investigation into this occurrence, the Bureau
simultaneously issues the following interim recommendations:



IR990072



The Bureau of Air Safety Investigation recommends that Saab
Aircraft AB fit the ice-speed modification of the stall warning
system to the worldwide fleet of Saab 340 aircraft, as a matter of
priority.



IR990073



The Bureau of Air Safety Investigation recommends that the Federal
Aviation Administration note the circumstances surrounding this
occurrence, and note the fact that the Bureau shares a number of
concerns regarding aircraft certification procedures, particularly
those involving flight in known icing conditions.



IR990074



The Bureau of Air Safety Investigation recommends that the Joint
Airworthiness Authorities note the circumstances surrounding this
occurrence, and note the fact that the Bureau shares a number of
concerns regarding aircraft certification procedures, particularly
those involving flight in known icing conditions.



IR990075



The Bureau of Air Safety Investigation recommends that
Luftfartsverket note the circumstances surrounding this occurrence,
and note the fact that the Bureau shares a number of concerns
regarding aircraft certification procedures, particularly those
involving flight in known icing conditions. The Bureau also
recommends that Luftfartsverket as the initial certifying agency of
the Saab 340 aircraft, review the certification aspects of the
aircraft's stall warning system, particularly in icing
conditions.

Organisation Response
Date Received
Organisation
Civil Aviation Safety Authority
Response Text

BASI Interim Recommendation IR990076, resulting from occurrence
9805068, recommends that CASA examine the circumstances surrounding
the stall of a SAAB 340 aircraft at Eildon Weir on 11th November
1998, and take whatever steps are necessary to ensure the safety of
SAAB 340 aircraft operating in Australia.



The occurrence report noted that the crew had selected engine and
propeller anti-ice systems on, but had not activated the leading
edge de-icing boots. The auto pilot was engaged, and the aircraft
slowed under the icing conditions until stall occurred. Airframe
buffet was experienced, but the crew mistook this buffet for
propeller vibration.



The report favourably notes modifications mandated by Transport
Canada. The report is thorough in evaluating the history of
de-icing problems in SAAB 340 and similar aircraft. However,
actions by the crew in this instance appear to have made a poor
situation worse. CASA therefore does not believe at this time that
there is an airworthiness problem with this aircraft type that
requires immediate mandatory action.



Also, you will be aware of the intense debate a decade ago on the
subject of Australian-specific design requirements for aircraft.
The debate resulted in Australia's design requirements in Part 101
of the Civil Aviation Orders being abandoned for aircraft types
that have civil certification in a major aviation country. The
public policy of CASA and the Government is now that CASA will
impose requirements additional to those of internationally accepted
certification standards only where those requirements can be
publicly justified, including cost-benefit considerations. The SAAB
340 and many other similar aeroplanes have been type certificated
to internationally accepted certification standards and the
argument for imposing the Canadian requirement on these aeroplanes,
or even the SAAB 340 in isolation, does not yet appear to be
adequate to meet CASA's criteria for an Australian-specific design
requirement.



Subsequent to the issue of this report, the US FAA has proposed
some major changes to the way that modern propeller aircraft are
handled under icing conditions. This includes a proposal to require
that de-icing boots be activated as soon as an aircraft encounters
icing conditions (FAA research has shown that "ice-bridging" is not
of concern with modern de-icing systems). There is likely to be
considerable discussion of these issues over the coming months, and
CASA will be keeping a close watch on developments.



Pending the outcome of the FAA proposal, CASA will



- write to Australian operators of this aircraft type to inform
them of the BASI investigation, and recommend they review their
training and operating procedures; and



- write to the manufacturer and associated regulatory authorities
to seek their views, and to elicit comments on appropriate
action.



We will provide you with information copies of this correspondence,
and keep you informed of any further action initiated.