Recommendation

The Civil Aviation Safety Authority accepts this recommendation
and will move to prepare a regulatory amendment to make it
mandatory for pressurised aircraft to have aural cabin altitude
alert warning systems. This amendment will follow the normal
regulatory development process which, in the first instance, will
lead to the circulation of a Discussion Paper. It is anticipated
that the paper will be released this month.

I refer to my letter to you of 2 February 2001 in response to
your recommendation R20000288.

I would like to clarify CASA's position which is that audible
alarms be made mandatory in all turbine powered pressurised
aircraft. This is presented as the preferred option in the
discussion paper which canvases industry views on the alternatives;
these include extending the requirement to all pressurised aircraft
or maintaining the current rule.



A copy of the discussion paper will be forwarded to you
shortly.

CASA is moving quickly to publish a Notice of Proposed Rule
Making (NPRM) on the above subject. Publication date is intended to
be before the end of April.



The objective of the Airworthiness Directive is to provide a
minimum acceptable standard for an aural warning system and to
fulfil ATSB Recommendation No. R20000288.

I am writing to advise you of the Civil Aviation Safety
Authority's (CASA's) final determination with regards to the
Australian Transport Safety Bureau's Recommendation 20000288 that
the Authority mandate the fitment of aural warnings to operate in
conjunction with the cabin altitude alert warning systems. As you
would be aware, the Deputy Prime Minister and Minister for
Transport and Regional Services has taken a close interest in this
recommendation for some time and has been pressing for a resolution
of this matter as soon as possible.



In December 2000, the ATSB issued Recommendation 20000288, stating
that `The ATSB therefore recommends that CASA mandate the fitment
of aural warnings to operate in conjunction with the cabin altitude
alert warning systems on all Beechcraft Super King Air and other
applicable aircraft'. I n February 2001, CASA advised the ATSB that
the Authority had accepted this recommendation. In its response,
CASA advised that the Authority had agreed to prepare a regulatory
amendment to make it mandatory for pressurised aircraft to have
aural cabin altitude alert warning systems.



To progress this regulatory amendment, CASA issued a Discussion
Paper (DP) and a Notice of Proposed Rule Making (NPRM) in order to
consult with members of the aviation industry. As CASA advised the
Bureau in April 2002, the objective of a proposed AD to follow the
NPRM was to provide a minimum acceptable standard for an aural
warning system and to fulfil R20000288. While the responses
received to both the DP and the NPRM included some support of the
proposal, key responses such as those from the Regional Aviation
Association of Australia and the Australian Federation of Air
Pilots did not provide favourable support.



The comments and subsequent information provided to CASA have
caused the Authority to carefully re-consider both the cost-benefit
analysis of the proposal, and its acceptance of Recommendation
20000288.



A number of respondents commented that R20000288 was based solely
on one incident (VH-OYA), and that that incident involved a newly
endorsed Royal Australian Air Force (RAAF) pilot on his first
flight as pilot in command of a Beech 200. The RAAF subsequently
reported to the ATSB a second pressurisation incident, which
occurred on 12 December 1999, involving VHOYA.

Some respondents objected to CASA's proposal on the grounds that
the incident involving VH-OYA was not typical of civil operations,
especially commercial operations with a multiple-crew. Many
respondents explained that the incident involving VH-OYA points to
the risk associated with inadequate training rather than a need for
additional hardware. In short, comments received by CASA indicated
that the nature of the flight conducted by VH-OYA was dramatically
different to operations conducted by those potentially affected by
the recommendation.



CASA's cost-benefit analysis for the mandatory fitment of aural
warnings was based on an assumed fatality rate in Australia caused
by unrecognised depressurisation. Several respondents highlighted
the fact that if this assumed fatality rate was extrapolated to the
United States of America the fatality rate would be so high that
the Federal Aviation Administration would respond immediately, with
CASA therefore only having to harmonise with the resulting
requirement.



CASA believes that if a cost-benefit analysis were to be based on
worldwide historical data for accidents caused by, or possibly
caused by, cabin depressurisation the result would not support
mandatory installation of aural warnings. This would certainly be
true of modern transport category aeroplanes whose warning systems
usually cannot be modified by the addition of simple, low-cost
aural warning systems.



CASA has been unable to find any support for the proposal to
mandate the fitment of aural warnings amongst foreign regulators
responsible for certification of affected aircraft, nor from the
manufacturers of these aircraft. However, it is noted that some
manufacturers are fitting aural warning devices in newer aircraft
types such as the Raytheon King Air B300.



For over a decade CASA, and its predecessors, have followed a
policy of international harmonization, in that uniquely Australian
requirements will not be introduced unless the requirement can be
justified on safety grounds. This policy accords with the Single
Worldwide Certification Code and the international desire to not
devalue aircraft by local modification.



I understand that CASA has recently been advised by De Havilland
Canada that the development of a system capable of satisfying the
proposal for the Dash 8 aircraft is estimated to cost $317,650
(CAD). This cost could be shared among the operators requiring the
retrofit but operators would be responsible for procuring and
installing the required parts, with subsequent flight-testing of at
least two hours.



The fatal accident involving VH-SKC in May 2000, focussed public
attention on the possibility that absence of an aural warning in a
pressurised aircraft may be a serious deficiency.



CASA notes that the Western Australian State Coroner, Mr Alastair
Hope, was unable in his findings regarding VH-SKC to confidently
attribute the accident to unrecognised depressurisation. Also, the
ATSB's final report concluded that 'due to the limited evidence
available, it was not possible to draw definitive conclusions as to
the factors leading to the incapacitation of the pilot and
occupants of VH-SKC.'



The Coroner subsequently concluded that `While it is possible that
the occupants of the aircraft died as a result of hypobaric
hypoxia, I cannot exclude the possibility that some unknown and
unidentified toxic fumes caused their incapacity and death ...'.
Nevertheless, Coroner Hope recommended that `an audible warning, to
operate in conjunction with the cabin altitude alert system, be
fitted to pressurized aircraft, such aural alert to be triggered by
a separate barometric switch from the visual alert system and at a
different cabin pressure altitude.'



In the absence of clear proof to the contrary, CASA is not
convinced that unrecognised depressurisation was the cause of the
accident involving VH-SKC and believes that this accident therefore
does not of itself justify the mandatory fitment of audible warning
devices.



The key issue is, of course, how do we proceed from here. CASA now
considers that it is not appropriate to mandate the fitment of
aural warning devices. While it would appear that fitment could be
achieved for some aircraft types at a reasonable cost,
manufacturers have advised us it would be prohibitive for other
types.



In view of the recent availability of low cost devices that may
provide safety benefits to some aircraft types, CASA proposes to
individually write to owners of affected aircraft types drawing
their attention to the devices and recommending their fitment be
considered. While these devices would be fitted on a 'no hazard, no
interference' basis and on the understanding that there is no
standard that would guarantee their functionality in the event of
an emergency, CASA intends to promote the potential benefit of
these systems, particularly for operators of the Beech 200 and
other pressurised single-pilot aeroplanes.



In light of the above, CASA's revised response to Recommendation
R20000288 is as follows:



CASA acknowledges the potential safety benefit in installing an
aural warning system in Beech 200 and other single-pilot
pressurised aeroplanes. However CASA does not consider the
potential safety benefits sufficient to warrant mandating the
fitment of aural warnings. CASA notes no manufacturer or certifying
Authority in the world requires mandatory fitment of such aural
warnings and the initiative is opposed by key industry stakeholders
in Australia.



CASA will however continue to strongly recommend aural cabin
pressure warning devices and will write to the registration holders
of all single-pilot pressurised aeroplanes, including the Beech
200, advising them of the availability of low-cost aural warning
systems and their benefit in relation to uncommanded cabin
depressurisation events.



Through continued safety education programmes, CASA will also
continue to inform pilots about hypoxia, the importance of
pressurisation management and the appropriate response to an
uncommanded depressurisation.



In view of CASA's commitment to consult with the aviation community
on all its proposed legislation I believe this is a sound and
defensible position for CASA to take in response to R20000288 and
meets the intent of what the ATSB was trying to achieve in its
recommendation and will serve to improve future aviation
safety.



I trust that this response will allow you to close this
recommendation.

On 27 May 2003, the Civil Aviation Safety Authority advised the
ATSB that the authority had issued the following letter dated 26
May 2003 to certificate of registration holders for pressurised
aircraft:





OWNERS AND OPERATORS AUSTRALIAN-REGISTERED PRESSURISED
AIRCRAFT



Aural cabin pressure warning system



In 2000 the Australian Air Transport Safety Bureau (ATSB)
recommended that the Civil Aviation Safety Authority (CASA) make it
mandatory for all Beech 200 and other applicable aircraft to be
equipped with an aural warning of low cabin pressure. This
recommendation' was based on an incident in which a Beech 200
aircraft suffered an uncommanded cabin depressurisation. The visual
warning system activated but the pilot's performance was degraded
to the point that he did not respond correctly. In that incident an
accident was avoided by the actions of a passenger.



On 4 September 2000 a Beech 200 aircraft took off from Perth and
flew for five hours before crashing in Queensland. There were no
survivors. The ATSB investigation concluded that while there are
several possible reasons for the pilot and passengers being
incapacitated, this was probably a result of hypobaric hypoxia due
to the aircraft being fully or partially unpressurised and the
occupants not receiving supplemental oxygen.



Cabin altitude significantly above 10,000 feet leads to hypoxia, a
condition of impaired human performance caused by inadequate oxygen
in the blood. One of the early symptoms of hypoxia is impairment of
vision and deterioration of situational awareness. There is general
consensus that when suffering hypoxia a pilot's ability to react to
an aural warning is impaired less rapidly than the ability to react
to a visual warning. In an uncommanded cabin depressurisation the
occupants' physical and mental functions will suffer progressive
impairment and early recognition and rectification of the situation
is vital.



Aural warning recommended



CASA responded to the ATSB recommendation by publishing a
Discussion Paper in 2001, and a Notice of Proposed Rule Making
(NPRM) in 2002. Both these consultation documents proposed that
CASA would issue an Airworthiness Directive to mandate an aural
cabin pressure warning in turbine engine pressurised aircraft. The
response of the aviation community to the NPRM was mixed, but the
most persuasive responses were opposed to CASA's proposed
action.

As a result, CASA decided not to mandate aural cabin pressure
warnings in any aircraft at this time. In particular, it was
indicated that the cost of mandatory fitting of aural warnings
could be prohibitive for some aircraft.



For many years CASA has however, strongly recommended that the
cabin pressure warning system in pressurised aircraft should
include an aural warning in addition to the visual warning.
Unfortunately, low-cost aural warning systems suitable for
installation in pressurised aircraft have not been available until
recently. At least two low-cost aural warning systems are now
readily available in Australia. CASA again strongly recommends
that, if your pressurised aircraft does not have an aural cabin
pressure warning, you seriously investigate installation of such a
warning system. The benefit to your pilots and passengers lies in
the reduction in risk of an uncommanded depressurisation leading to
an incident or fatal accident. The benefit is much greater than the
cost of purchase and installation of one of these low-cost
systems.



Safety measure



An aural cabin pressure warning system is a positive safety measure
for all pressurised aircraft. Clearly, the benefit could be
substantial in an aircraft operated by a single pilot. The benefit
could also be substantial in an aircraft that routinely operates at
high altitude, say above 18,000 feet. If your pressurised aircraft
does not have aural cabin pressure warning and is routinely
operated above 18,000 feet by a single pilot CASA strongly
recommends you give prompt consideration to installation of an
aural cabin pressure warning system.



Two Australian manufacturers have approached CASA to demonstrate
low-cost aural cabin pressure warning systems which are now in
production:



Aironautical Electronics Corporation

Phone: 08 8362 4142

Fax: 08 8362 4194

Web: www.airocorp.com

See advert in Flight Safety Australia



Electric Force Measurement

Phone: 03 955& 5741

Fax: 03 9558 5741

Web: www.hotkey.net.au/-efm/



While CASA has not made it mandatory for pressurised aircraft to be
equipped with aural cabin pressure warning systems at this stage,
we strongly encourage each operator of a pressurised aircraft to
give serious consideration to the benefit of voluntarily installing
such a system if the aircraft presently has only a visual warning
system.

The following response was received from the Civil Aviation
Safety Authority on 23 April 2004.



Despite information of the availability of aural warnings being
made available to members of the aviation industry, CASA
understands that the "take up rate" for the installation of these
devices is very low.



ATSB Comment:



The ATSB has classified this response as MONITOR, which means that
the ATSB is keeping a watching brief on further safety issues
related to cabin pressurization.