Recommendation

The certification basis for the Beech 200 and similar aircraft,
which is accepted by Australia and the Joint Aviation Authorities,
requires provision of a warning indication to the pilot when a set
pressure differential is exceeded and when the cabin altitude is
above 10,000 feet. There is no specification of the type of warning
system required for Commuter Category aircraft. It should be noted
that even for Transport Category aircraft, the warning indication
may be "aural or visual".



Whilst CASA accepts the Bureau's point that the onset of hypoxia
usually degrades visual acuity before hearing, this incident does
not provide sufficient justification to mandate retrofitting of
audible cabin altitude warning. There have been more than 2,000 of
the type produced and the design is well proven.



Before imposing such a condition on operators, extensive
consultation would need to be undertaken. The Authority will await
the outcome of IR19990153 and IR19990155 before contemplating
further action on this matter.

AUDIBLE WARNINGS



As was indicated to you by letter on 21 January 2000, CASA wished
to consider the responses of the aircraft manufacturer (Raytheon
Aircraft Company) to IR19990153 and the United States Federal
Aviation Administration (FAA) to IR19990155 before contemplating
further action on this matter. Now that the ATSB has provided CASA
with responses from these organisations we are in a position to
comment further.



CASA notes the response of the FAA which includes advice that,
although it is recognised that adding an aural warning is a
desirable enhancement of the system, requiring such a warning for
the existing fleet is not considered necessary to meet the minimum
airworthiness standards. This is consistent with CASA's view, first
put in an Air Navigation Order (108.26) issued in June 1972 by the
then Department of Aviation, which included the following:



Note: ".. The cabin pressure warning should not depend on the
reading of a gauge. An aural warning is strongly
recommended."



This recommendation remains current as Civil Aviation Order (CAO)
108.26.



CASA also notes that, in response to IR19990153, Raytheon Aircraft
Company states that the warnings provided are more than adequate to
meet the certification requirements of the Model B200. The response
goes on to say that there are over 1,600 Model 200 King Airs in
operation worldwide with this system installed and the company does
not believe it is necessary to add aural warning to an already
proven visual system.



You have informed us that accident and incident reports currently
available to the ATSB from the UK, the United States and New
Zealand, relating to some 200 incidents involving turbo prop and
piston engine pressurised aircraft, do not contain any reports of
failure of the existing warnings to alert the crews to
pressurisation failures. The only possible exception is the
incident involving VH-OYA on 21 June 1999 (where the alerting
system may have failed and the automatic deployment of the
passenger oxygen masks did fail), which is the subject of the
Interim Report.



CASA therefore believes that there is no valid evidence currently
available to support mandating the fitting of an audible warning on
pressurised aircraft. CASA recognises that an audible warning is a
useful defence mechanism. Safety promotion material will be
prepared which will emphasise the position defined in CAO 108.26
strongly recommending an aural warning.



OPERATIONAL FACTORS



On the basis of the information in the interim report and provided
by the ATSB at the meetings on 7 and 15 September, CASA is of the
view that a significant factor in the June 1999 incident was the
failure of the crew to follow correct operating procedures.



While recognising that physical failures of the aircraft involving
the oxygen mask drop down system and the barometric switch
associated with the warning system have been addressed, CASA's
operational and human factor specialists have expressed concern
that the Interim Report on the incident in June 1999 did not
address key training, operational and human performance
issues.



For example, the ATSB advised that the RAAF crew had used both a
civilian and military check list and, apparently, had still failed
to set the pressurisation system and had failed to detect that the
aircraft was not pressurising as called for in the check list
following take-off, and again when passing through 10,000 ft.



ATSB indicated that there had been some discussion with the Defence
Forces on this issue and that crew training had been amended to
reflect civil requirements. Of course, this does not address the
question of whether the civil training requirements are appropriate
and effective.



At present, CASA's view is that the training and procedural issues
evident in the June 1999 incident were the most significant factors
in the events leading up to the pilot's incapacitation, and the
physical aircraft failures were the main reason the errors were not
picked up earlier.



While it is acknowledged that an aural alarm would provide an
additional means of alerting the crew to a depressurisation or no
pressurisation, there appears to be insufficient human factors
research to indicate that such an alarm would, in isolation, be
sufficient to resolve the problem. Improved crew training and
adherence to proper operating procedures would appear to offer the
most effective way of ensuring the correct operation of all
aircraft systems.





OTHER SIMILAR INCIDENTS



At the meeting on 15 September, the ATSB indicated that it was
aware of a second incident with a RAAF aircraft since the incident
that had resulted in the Interim Recommendation. At the present
time, neither the ATSB or the Department of Defence have been able
to confirm that there was a second incident. In the event that a
second incident did occur, it would be useful to examine the
circumstances to determine what lessons need to be learned in
relation to crew training and adherence to operational procedures.
It would also be useful to ascertain whether the purported second
RAAF incident occurred before or after Defence had changed its
training for these aircraft.



CASA notes the advice from the ATSB that, to date, no conclusions
could be drawn from the preliminary investigation of the Beech
Super King Air 200 aircraft in Queensland. CASA has not ruled out
the mandating of aural warnings to operate in conjunction with the
cabin altitude alert systems on Raytheon King Airs should evidence
supporting this action emerge during the investigation, while
noting that this requirement would almost certainly have to be
extended to apply to all piston and turbo prop pressurised aircraft
types. As you know, as part of the industry, consultation process,
the Authority is required to prepared a Regulatory Impact Statement
(RIS). The RIS would have to include a discussion on other options
that would be available to address the safety concerns identified
by the ATSB. CASA would have to be satisfied on all the evidence
available that the fitment of an aural warning device would be the
most effective and appropriate way of resolving these safety
concerns.





CASA ACTIONS



CASA is seeking further advice from the FAA on contemporary human
factors research into the issue of aural verses visual alerting
systems. We would welcome any further advice that the ATSB has been
able to obtain from other sources overseas on this issue.



We regard an audible warning as a good fourth or fifth line of
defence, but believe that prevention, via training and promulgating
of safety information, is more important than finding another
cure.



CASA will convene a series of Major industry Workshops. At these
safety promotion and educational material will be provided to
discuss hypoxia and other matters relevant to operation of
pressurised aircraft. It is also intended to emphasise operational
and training issues to ensure repeat omission of action on
checklist items is highlighted and addressed. I believe it is
essential that ATSB form part of these workshops to put forward
their views and evidence on pressurisation incidents. In this way
we can ensure that industry participants are made aware of all the
safety issues involved and can also contribute to a debate on the
solutions available, including that of mandatory audible
warnings.

In 1999 ATSB issued Interim Recommendation IR19990154. CASA
responded to that Recommendation on 28 January 2000. That response
began by stating:



"The certification basis for the Beech 200 and similar aircraft,
which is accepted by Australia and the Joint Aviation Authorities,
requires provision of a warning indication to the pilot when a set
pressure differential is exceeded and when the cabin altitude is
above 10000 feet."



This statement is misleading and deserves clarification. The
certification basis for the Beech 200 and many other aeroplanes
with a maximum take-off weight not exceeding 12,500 lb (5670 kg) is
Part 23 of the Federal Aviation Regulations of the USA. In February
1977, at amendment 23-17, Part 23 was amended to state that
aircraft with pressurised cabins must have a visual or aural
warning of depressurisation when the cabin pressure altitude
exceeds 10,000 ft. Prior to amendment 23-17 Part 23 stated that a
visual or aural warning must be provided but did not nominate a
cabin pressure altitude at which the warning must activate.



The Beech 200 is certificated in the USA to Part 23 at amendment
23-9. Therefore in the USA no Beech 200 aircraft is required to
have a warning of cabin depressurisation at 10,000 ft. All Beech
200 aircraft are equipped with a visual warning which activates at
a nominal cabin pressure altitude of 12,500 ft.