As a result of this investigation, a number of safety actions
have been undertaken.
Local safety actions
The operator has re-evaluated pilot training procedures,
realigning them with the syllabus in the operator's check and
training manual.
More stringent currency requirements have now been put in place
for single pilot operations by military pilots on this
aircraft.
A program has been put in place to conduct regular maintenance
of the cabin altitude warning and the supplemental oxygen
systems.
The operator has installed an aural warning system in the Super
King Air 200 aircraft that was involved in this incident. The
operator is also fitting aural warning systems that interface with
the cabin pressure altitude warning to the rest of their Super King
Air 200 aircraft fleet. These systems are being fitted at an
approximate unit cost of $1,000. Consideration is also being given
to the installation of similar systems to their other pressurised
turbo-prop aircraft.
The Australian Defence Force, Directorate of Flying Safety has
also published articles on hypoxia, related to this occurrence, in
its 'Flying Feedback' and 'Spotlight' magazines. These magazines
are distributed to military flight crew.
Recommendations
The Australian Transport Safety Bureau (formerly the Bureau of
Air Safety Investigation) issued interim recommendations,
IR19990084, IR19990088, IR19990089, IR19990090, IR19990150,
IR19990151, IR19990152, IR19990153, IR19990154 and IR19990155
during the investigation. The responses to these recommendations,
without alteration to the text, are included at Annex B.
As a result of this investigation the following recommendations
are issued simultaneously with this report.
R20000289
The ATSB recommends that CASA advise relevant operators of its
interpretation of CAO 108.26 in relation to the applicability of
the requirements for a device to provide the flight crew of
pressurised aircraft with a warning whenever the cabin pressure
altitude exceeds 10,000 feet.
The following response was received from CASA on 02 February
2001:
The Civil Aviation Safety Authority accepts this
recommendation and is now considering how best to clarify the
intent of CAO 108.26, paragraph 3.1, for relevant
operators.
ATSB RESPONSE STATUS: CLOSED - ACCEPTED
R20000288
The ATSB has concerns regarding the ineffectiveness of visual cabin
altitude warning systems that are not accompanied by an aural
warning. In this incident the inclusion of an audible warning, as
strongly recommended in CAO 108.26, may have assisted the pilot to
recognise a depressurisation.
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.
The following response was received from CASA on 02 February
2001:
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.
ATSB RESPONSE STATUS: CLOSED - ACCEPTED
In accordance with normal procedures the ATSB will continue to
monitor CASA's implementation of the recommendations.
ATTACHMENTS
Attachment A - Human Factors, Cabin Altitude Alert Warning
System
Attachment B - Responses to Previously Issued Recommendations
Arising From Occurrence 199902928.
Attachment A
Human Factors, Cabin Altitude Alert Warning System
There are many complex factors associated with this occurrence
but one of the human factors issues that the team examined was the
cabin altitude alerting/warning system.
The Bureau examined this issue from a human factors perspective
rather than as a certification issue. The rationale for
recommendation IR 19990153, IR 19990154, and IR 19990155 was as
follows:
Warnings
When designed correctly, auditory warning signals can improve
operator performance and reduce accidents (Edworthy, Loxley, &
Dennis, 1991). It is important to ensure that appropriate warning
system information is presented in a form that individuals or crews
can readily understand, and at the right time to facilitate making
effective judgements and decisions (Noyes et al., 1995). In
particular, ' the alerting function for all important failures
should be fulfilled by a [sic] audio warning…' (Green et al., 1991,
p. 120). Moreover, auditory warnings should be used when a
situation calls for immediate action (Deatherage, 1972; Sanders
& McCormick, 1992; Sorkin, 1987). Cabin depressurisation is an
example of such an important failure. Furthermore, compliance rates
for visual warnings are often low (Edworthy, Stanton, &
Hellier, 1995; Wogalter, Kalsher, & Racicot, 1993). However,
research has demonstrated that reaction times to visual indications
are shorter when supported by an auditory warning signal (Selcon,
Taylor, & McKenna, 1995; Stokes & Wickens, 1988). Finally,
auditory warnings have an immediacy that may not be apparent with
visual warnings and they may also produce higher levels of
compliance (Stokes & Wickens, 1988; Wogalter et al., 1993).
Hypoxia
Research has demonstrated that vision is particularly sensitive
to hypoxia (Fowler, Paul, Porlier, Elcombe, & Taylor, 1985;
Ernsting, Sharp, & Harding, 1995). In addition, visual
degradation occurs before the auditory modality declines
(Brinchmann-Hansen & Myhre, 1989; Fowler, Banner, & Pogue,
1993; Fowler, Elcombe, Kelso, & Porlier, 1987; Fowler, Paul,
Porlier, Elcombe, & Taylor, 1985; Green, Muir, James, Gradwell,
& Green, 1999; Nesthus, Garner, Mills, & Wise, 1997; Orlady
& Orlady, 1999; U.S. Navy Flight Surgeon's Manual, 1993).
Moreover, the rate and magnitude of decline of the visual modality
in a hypoxic individual is more rapid compared to the auditory
modality. Moderate and severe hypoxia causes a restriction of the
visual field, with loss of peripheral vision and the development of
a central scotoma. There may also be a subjective darkening of the
visual field. Auditory acuity is also reduced by moderate and
severe hypoxia, but some hearing is usually retained even after
other senses such as vision are lost (Ernsting, Sharp, &
Harding, 1995).
Conclusion
Therefore, the incorporation of an aural warning to supplement
the visual warnings associated with the cabin altitude alert system
would provide greater assurance for the integrity of the
system.
References and relevant research
Bliss, J, P., Gilson, R. D., & Deaton, J. E. (1995). Human
probability matching behaviour in response to alarms of varying
reliability. Ergonomics, 38, 2300-2312.
Brinchman-Hansen. O, & Myhre, K. (1989). Effect of hypoxia
on the macular recovery time in normal person. Aviation, Space, and
Environmental Medicine, 60, 1183-1186.
Deatherage, B. H. (1972). Auditory and other sensory forms of
information presentation. In H.P. VanCott & R.G. Kinkade
(Eds.), Human engineering guide to equipment design (pp. 123-160).
Washington, DC: US Govt. Printing Office.
Edworthy, J. (1997). Cognitive compatibility and warning design.
Ergonomics, 1, 193-209.
Edworthy, J., Loxley, S., & Dennis, I. (1991). Improving
auditory warning design: Relationship between warning sound
parameters and perceived urgency. Human Factors, 33, 205-232.
Edworthy, J., Stanton, N., & Hellier, E. (1995). Warnings in
research and practice: Editorial. Ergonomics, 38, 2145-2154.
Edworthy, J., & Stanton, N. (1995). A user-centred approach
to the design and evaluation of auditory warning signals: 1.
Methodology. Ergonomics, 38, 2262-2280.
Ernsting, J. & Sharp, G. R., revised by Harding, R. M.
(1995). Hypoxia and hyperventilation. In J.Ernsting & P.King
(Eds.), Aviation medicine (2nd Edition) (pp. 45-59). Oxford, UK:
Butterworth-Heinemann Ltd.
Fowler, B., Banner, J., & Pogue, J. (1993). The slowing of
visual processing by hypoxia. Ergonomics, 36, 727-735.
Fowler, B., Elcombe, D. D., Kelso, B., & Porlier, G. (1987).
The threshold for hypoxia effects on perceptual-motor performance.
Human Factors, 29, 61-66.
Fowler, B., Paul, M., Porlier, G., Elcombe, D. D., & Taylor,
M. (1985). A re-evaluation of the minimum altitude at which hypoxic
performance decrements can be detected. Ergonomics, 28,
781-791.
Green, R. G., & Morgan, D. R. (1985). The effects of mild
hypoxia on a logical reasoning task. Aviation, Space, and
Environmental Medicine, 56, 1004-1008.
Green, R. G., Muir, H., James, M., Gradwell, D., & Green, R.
L. (1991). Human factors for pilots. Aldershot, UK: Ashgate.
Izraeli, S., Avgar, D., Glikson, M., Shochat, I., Glovinsky, M.
D., & Ribak, J. (1988). Determination of the 'time of useful
consciousness' (TUC) in repeated exposures to simulated altitude of
25,000 ft (7, 620 m). Aviation, Space and Environmental Medicine,
59, 1103-1105.
Letourneau, J. E., Denis, R., & Londorf, D. (1986).
Influence of auditory warning on visual reaction time with
variations of subjects' alertness. Perceptual & Motor Skills,
62, 667-674.
McCarthy, D., Coban, R., Legg, S., & Faris, J. (1995).
Effects of mild hypoxia on perceptual-motor performance: A
signal-detection approach. Ergonomics, 39, 1979-1992.
Naval Aerospace Medical Institute. (1991). Physiology of flight.
In R.K. Ohslun.
C.I. Dalton, G.G. Reams, J.W. Rose, & R.E. Oswald (Eds.),
United States Naval flight surgeon's manual (3rd edition)
(http://www.vnh.org//FSManual/01/03Hypoxia.html). Iowa City, Iowa:
University of Iowa College of medicine in collaboration with The
Bureau of medicine and Surgery, Department of the Navy.
Nesthus, T. E., Garner, R. P., Mills, S. H., & Wise, R. A.
(1997, March). Effects of simulated general aviation altitude
hypoxia on smokers and nonsmokers (FAA Office of Aviation Medicine
Reports FAA-AM-97-07). Washington, DC: FAA.
Noyes, J. M., Starr, A. F., Frankish, C. R., & Rankin, J. A.
(1995). Aircraft warning systems: application of model-based
reasoning techniques. Ergonomics, 38, 2432-2445.
Orlady, H. W., & Orlady, L. M. (1999). Human factors in
multi-crew operations. Aldershot, UK: Ashgate.
Sanders, M. S., & McCormick, E. J. (1992). Human factors in
engineering and design (7th Ed). New York: McGraw-Hill.
Satchell, P. M. (1993). Cockpit monitoring and alerting systems.
Aldershot, UK: Ashgate.
Selcon, S. J., & Taylor, R. M. (1995). Integrating multiple
information sources: using redundancy in the design of warnings.
Ergonomics, 38, 2362-2370.
Sorkin, R. D. (1987). Design of auditory and tactile displays.
In G. Salvendy (Ed.), Handbook of human factors. New York: John
Wiley.
Stanton, N. A., & Edworthy, J. (Eds.) (1999). Human factors
in auditory warnings. Aldershot, UK: Ashgate.
Stokes, A. F., & Wickens, C. D. (1988). Aviation displays.
In E. L. Wiener & D. C. Nagel (Eds.), Human factors in aviation
(pp. 387-431). San Diego, CA: Academic Press.
Takagi, M., & Watanabe, S. (1999). Two different components
of contingent negative variation (CNV) and their relation to
changes in reaction time under hypobaric hypoxic conditions.
Aviation, Space, and Environmental Medicine, 70, 30-34.
Wogalter, M. S., Kalsher, M. J., & Racicot, B. M. (1993).
Behavioural compliance with warnings: effects of voice, context,
and location. Safety Science, 16, 637-654.
Attachment B
Responses to previously issued recommendations arising from
occurrence 199902928
The Australian Transport Safety Bureau classifies the responses
to recommendations as follows:
CLOSED - ACCEPTED
ATSB accepts the response without qualification.
CLOSED - PARTIALLY ACCEPTED
ATSB accepts the response in part but considers other parts of the
response to be unsatisfactory. However, ATSB believes that further
correspondence is not warranted at this time.
CLOSED - NOT ACCEPTED
ATSB considers the response to be unsatisfactory but that further
correspondence is not warranted at this time.
OPEN
The response does not meet some or all of the criteria for
acceptability for a recommendation that ATSB considers to be
significant for safety. ATSB will initiate further
correspondence.
The following interim recommendations were issued during the
investigation.
IR19990084, issued on the 28 July 1999
The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority issue a directive for an immediate check
of the fitment of passenger oxygen system mask container doors on
all Australian Beech King Air B200 aircraft and, all other aircraft
similarly equipped.
Response:
The following response to IR 19990084 was received from the Civil
Aviation Safety Authority on 16 September 1999:
In response to the subject recommendation, CASA has
considered the issue of a directive to check the installation of
passenger oxygen system mask container doors on all Australian
Beechcraft King Air B200 aircraft, and similarly equipped aircraft.
The BASI recommendation notes that the maintenance manual has a
cautionary note regarding potential for incorrect fitment of the
passenger oxygen mask container doors. In view of this, CASA does
not consider issue of an Airworthiness Directive to comply with
existing maintenance instructions is warranted.
An advisory letter (copy attached) was sent to all Certificate
of Registration holders of Raytheon pressurised twin-engine
aircraft, in line with the 30 June 1999 interim advice that BASI
provided to CASA, to raise awareness of the incident with affected
operators of the aircraft. The letter strongly recommended checking
each passenger oxygen system mask container door for correct
installation, but did not make such a check mandatory. An
Airworthiness Advisory Circular, AAC 1-112, was also issued. No
further reports of incorrectly installed passenger oxygen masks
have been received by CASA.
Further action will be considered when the BASI final report
into the incident is made available.
Letter issued by CASA, dated 2 July 1999 to:
Certificate of Registration Holders
All Beech pressurised twin engine aircraft
Relating to: Faulty installation of emergency oxygen system
cover plates.
A recent incident involving a Beech 200 aircraft has highlighted
a potential safety hazard with the cover plates on the emergency
oxygen system. This letter is to draw your attention to the
deficiency in order that you may take appropriate actions for the
safety of persons flying in your aircraft. Although found on a
Beech 200, any Beech aircraft with an emergency oxygen system may
be similarly affected.
Following an incident involving the emergency oxygen system, a
maintenance investigation was carried out. Although not the primary
cause of failure, this investigation found that some of the covers
over the passenger mask headliner compartments had been incorrectly
installed. If the emergency oxygen system had been activated,
automatically or manually, the incorrectly installed covers would
not release and the oxygen masks would be unavailable. The operator
of the incident aircraft has since inspected four other Beech 200
aircraft. These four aircraft are maintained by a different
maintenance organisation. Of the four aircraft, two had oxygen mask
covers improperly installed such that they would not be able to
operate.
The covers are designed to be pushed open by a plunger which is
operated by pressure in the oxygen line. If the cover is installed
180 degrees out of proper position the plunger no longer contacts
the striker block fixed to the cover, and the cover remains in
place. The Beech 200 maintenance manual notes that caution should
be exercised when installing the cover plate. However, when the
cover is fitted there are no obvious signs which show that the
cover is not properly installed.
When more details are available CASA will contact the
manufacturer to determine what further actions may be required to
prevent incorrect installation of the covers.
The Civil Aviation Safety Authority strongly recommends an
inspection, or test, to ensure that each oxygen mask cover is
installed properly as shown in the applicable aircraft maintenance
manual at the earliest opportunity. The inspection, or test, should
confirm that the striker block in the cover is located below the
plunger. If any cover is found to be fitted incorrectly, remove and
refit the cover correctly and notify CASA through your nearest
district office.
ATSB RESPONSE STATUS: CLOSED-ACCEPTED.
IR19990088, issued on the 28 July 1999
The Bureau of Air Safety Investigation recommends that Raytheon
Aircraft issue a directive for an immediate check of the fitment of
passenger oxygen system mask container doors on all Beech King Air
B200 aircraft and, all other Raytheon aircraft similarly
equipped.
Response:
Raytheon Aircraft Company response received 11 January 2000.
RAC has published King Air Series Communique 99-005,
dated October 1999 (copy enclosed). RAC also published Safety
Communique No. 168 (copy enclosed), dated November 1999 and
applicable to all Raytheon Aircraft models with deployable
passenger oxygen mask systems, to ensure that all operators are
aware of the importance of properly installing the doors on the
oxygen mask boxes.
Additional Federal Aviation Administration response received 11
January 2000.
Raytheon Aircraft has reported that they do not intend
to issue a directive for an immediate check of the fitment of the
passenger oxygen system container doors. However, they have
published the safety communique noted above. Additionally, Raytheon
intends to revise the maintenance manual for the Model 300 series
King Airs to provide a cautionary note similar to that provided in
the 200 Series maintenance Manual.
ATSB RESPONSE STATUS: CLOSED-ACCEPTED.
IR19990089, issued on the 28 July 1999
The Bureau of Air Safety Investigation recommends that the
Federal Aviation Administration issue a directive for an immediate
check of the fitment of passenger oxygen system mask container
doors on all Beech King Air B200 aircraft and, all other aircraft
similarly equipped.
Response:
The following response was received from the US Federal Aviation
Administration on 11 January 2000.
The Raytheon Aircraft maintenance manual for the Beech
Super King Air 200 Series airplanes requires that an oxygen system
functional test be performed at the Phase 1 and Phase 3
inspections. This results in an initial inspection at 200 hours and
subsequent inspections every 400 hours. During each oxygen system
inspection, the operator is required to ensure that the doors on
the mask containers open and the masks drop out. Additionally, the
Model 200 Series Maintenance Manual cautions operators that the
oxygen 'Container door can be positioned 180 degrees off. If this
happens, the plunger cannot push the door open when activated.'
Other similarly equipped aircraft have the same oxygen system
maintenance schedule. The Model 300 Series Maintenance Manual does
not have the additional cautionary note.However, Raytheon has committed to revising this manual to add a
similar note to that in the Model 200 manual. To provide an added
level of awareness to operators, Raytheon Aircraft has published an
article regarding this subject in a King Air Model Communique. The
Communique will be mailed to all operators of Raytheon aircraft
equipped with auto-deploy oxygen masks to ensure that all operators
are aware of the importance of properly installing the doors on the
oxygen mask boxes. Considering the maintenance instructions already
in place, issuance of an Airworthiness Directive for an immediate
check of the fitment of passenger oxygen system mask container
doors would not significantly add to the safety of the fleet.In conclusion, this office recommends the Safety Recommendations
be closed. No further ACO action is required or planned.
ATSB RESPONSE STATUS: CLOSED-PARTIALLY ACCEPTED.
IR 19990090, issued on the 28 July 1999
The Bureau of Air Safety Investigation recommends that Raytheon
Aircraft examine and implement methods of preventing incorrect
passenger oxygen system mask container door fitment as installed in
Beech King Air B200 series aircraft, and all other Raytheon
aircraft similarly equipped.
Response:
Raytheon Aircraft Company response received 11 Jan 2000.
RAC will make a production design change to the B200
oxygen mask containers to provide a method of preventing the doors
from being installed incorrectly. RAC will make available through
spares, and announce via a Recommended Service Bulletin, the same
change to all delivered airplanes. The production design change is
tentatively scheduled to be completed by the end of the second
quarter of 2000.RAC has investigated to determine whether the condition
referenced in the Interim Recommendation might exist in other
Raytheon King Air model airplanes:
- The Model C90A does not have an auto-deploy or drop-down
system. It is totally passenger operated (i.e., the passenger opens
the door and plugs in the mask).- The Model B300 is an auto-deploy system made by Puritan
Bennett. The lid is permanently attached to the box with two metal
lanyards. The lanyards are not long enough to allow the door to be
rotated and installed improperly.- Model 200 serials BB-1 through BB-54 (excluded from the
applicability of the B200 system) use the same system as the Model
C90A.- The Model F90 has an oxygen system design similar to the B200.
The Interim Recommendation therefore applies to the Model F90 as
well. RAC will address the F90 in all corrective actions.- The Model 100 has an oxygen system design similar to the C90A.
It does not have an auto-deploy or drop-down system. It is totally
passenger operated (i.e., the passenger opens the door and plugs in
the mask).In addition to the King Air Models, RAC has investigated to
determine whether the condition referenced in the Interim
Recommendation might exist in other Raytheon model airplanes. The
investigation revealed that the condition does not exist.Specifically:
- The Commuter Airplane Series (Model 1900, 1900C, and 1900D)
oxygen box door design does not allow the door to be installed
backwards or in any other manner which would prevent the plunger
from releasing the door.- The Beechjet Airplane Series (Model 400, 400A, 400T) design
does not permit the oxygen doors to be installed backwards.- The Starship (Model 2000) does not have the same cover design
and cannot be installed backwards. The hinge tabs are on one side,
and the plunger interface is on the other. The plunger interface is
part of the door. There are no slots for the hinge tabs on the
other side of the box, so that the door cannot be installed 180
degrees out. Also, the plunger cannot be inserted into the valve
body if the door is backwards.- The Hawker Airplane Series design does not permit the oxygen
doors to be installed backwards.This information has also been supplied to the U.S. FAA.
Additional Federal Aviation Administration response received 11
January 2000.Raytheon Aircraft has committed to make a production
change to the B200 oxygen mask containers to provide a method of
preventing the doors from being installed incorrectly. The Model
300 is no longer in production. Raytheon will also make available
through spares via a recommended service bulletin the same change
to all delivered airplanes. The production design change is
scheduled to be completed by the end of the second quarter of 2000.In conclusion, this office recommends the Safety Recommendation
be closed. No further ACO action is required or planned.
ATSB RESPONSE STATUS: CLOSED-ACCEPTED.
IR 19990150, issued on the 7 October 1999
The Bureau of Air Safety Investigation recommends that Raytheon
Aircraft develop and publish methods for the in-situ testing of the
automatically deployable passenger oxygen activation system and the
cabin altitude alert system on Beechcraft aircraft, to ensure
complete system operation.
Response:
Raytheon Aircraft Company Response dated 10 July 2000
In accordance with Interim Recommendation IR19990150,
RAC has reviewed the B200 Maintenance Manual Procedures for
Functional Test Procedure of the Oxygen Auto-deploy System, and
finds it appropriate for the system. However, there is no
functional test for either of the barometric switches (one for the
oxygen system and one for the annunciator system) installed in the
airplane. RAC will add a procedure to the maintenance manual to
functionally check the barometric pressure switches.RAC reviewed the maintenance manual and found that there is a
'press to test' (which checks the annunciator lights). In the
oxygen system functional test procedure, one of the steps is to
verify the oxygen indicator light (green, in the caution/advisory
panel) is illuminated. These tests meet the certification
requirements for the airplane.Therefore, RAC plans no revisions to the Maintenance Manual with
regard to functional test of the oxygen system.
ATSB RESPONSE STATUS: CLOSED-ACCEPTED
IR19990151, issued on the 7 October 1999
The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority reassess the appropriateness of the
current maintenance procedures for the testing of automatically
deployable passenger oxygen systems and cabin altitude alert
systems, to ensure complete system operation.
Response:
To date no response has been received from CASA to this interim
recommendation.
IR19990152, issued on the 7 October 1999
The Bureau of Air Safety Investigation recommends that the
Federal Aviation Administration reassess the appropriateness of the
current maintenance procedures for the testing of automatically
deployable passenger oxygen systems and cabin altitude alert
systems, to ensure complete system operation.
Response:
Federal Aviation Administration Response received 31 March
2000.
In assessing Safety Recommendation 99.400, the B200
Maintenance Manual procedures for functional testing of the oxygen
auto-deploy system and the cabin altitude alert system were
reviewed. The procedures were found to be acceptable with the
exception of functional testing of the two barometric pressure
switches (one for the oxygen system and one for the annunciator
system) installed in the airplane. There is currently no provision
to functionally cheek the operation of either switch to ensure that
it would provide the required signal at the specified cabin
altitude of 12,500 feet. To address this issue, Raytheon Aircraft
Company has agreed to revise the affected maintenance manuals to
add a procedure to functionally check both barometric pressure
switches referred to above.In conclusion, this office considers the actions identified in
this letter to be satisfactory in addressing the safety concern.
Raytheon Aircraft Company has committed to making the necessary
changes to the maintenance manuals of the affected airplanes to
verify that the barometric pressure switches will actuate at the
required altitude. Therefore, the Wichita ACO recommends that
Safety Recommendation 99.400 be closed.
ATSB RESPONSE STATUS: CLOSED-ACCEPTED.
IR19990153, issued on the 7 October 1999
The Bureau of Air Safety Investigation recommends that Raytheon
Aircraft consider the incorporation of an audible warning to
operate in conjunction with the cabin altitude alert system on all
Beech aircraft so equipped.
Response:
Raytheon Aircraft Company Response received 18 July 2000
The 200 Series King Air's Annunciator system consists
of a warning annunciator panel with red readouts in the center of
the glareshield. Two red master warning flashers are located in the
glareshield, one in front of the pilot and one in front of the
co-pilot. The altitude warning annunciator triggers the master
warning system.The annunciators are the 'word readout' type. Whenever a fault
condition covered by the annunciator system occurs, a signal is
generated and the appropriate annunciator is illuminated. If the
fault requires the immediate attention and reaction of the pilot,
the appropriate red warning annunciator in the warning annunciator
panel illuminates and both master warning flashers begin flashing.
Any illuminated lens in the warning annunciator panel will remain
on until the fault is corrected.Therefore, in the case of the subject incident, even though the
pressurization system was not turned on, the pilot would have been
presented with a red flashing light and a red 'ALT WARN' when the
cabin altitude exceeded 12,500 feet. These two warnings are more
than adequate and meet the certification requirements of the Model
B200. There are over 1,600 Model 200 King Airs in operation
worldwide with this system installed. Raytheon Aircraft does not
believe it is necessary to add aural warning to an already proven
visual system.
ATSB RESPONSE STATUS: CLOSED-NOT ACCEPTED
IR19990154, issued on the 7 October 1999
The Bureau of Air Safety Investigation recommends that the Civil
Aviation Safety Authority consider the incorporation of an audible
warning to operate in conjunction with the cabin altitude alert
system on Beech aircraft, and other aircraft so equipped.
Response:
The following was issued from the Civil Aviation Safety Authority
on the 28 January 2000:
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. 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 2000 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.
The following was issued from the Civil Aviation Safety
Authority on the 29 September 2000:
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.We would be happy to meet with you again to share our views on
these workshops.ATSB RESPONSE STATUS: CLOSED-PARTIALLY ACCEPTED
IR19990155, issued on the 7 October 1999 The
Bureau of Air Safety Investigation recommends that the Federal
Aviation Administration consider the incorporation of an audible
warning to operate in conjunction with the cabin altitude alert
system on Beech aircraft, and other aircraft so equipped.
Response:
Federal Aviation Administration response received 31 March
2000.
Safety Recommendation 99.401, which requests
consideration of an audible warning to operate in conjunction with
the existing visual warning system, has also been reviewed. The
existing system utilizes a red 'ALT WARNING' annunciator light.
Although no aural tone is present when the red light illuminates,
both master warning flashers begin flashing to bring the pilot's
attention to the appropriate annunciator. In reviewing this
recommendation, the certification basis for the Raytheon Model 200
Series airplanes was reviewed. At the amendment level established
in the certification basis, Section 23.841 (f) states: '...an aural
or visual signal (in addition to cabin altitude indicating means)
meets the warning requirement for absolute cabin pressure limits'.
Furthermore, the corresponding Part 25 (Transport Category)
requirement (Section 25.841(b)(6)) states: '...an aural or visual
signal (in addition to cabin altitude indicating means) meets the
warning requirements for cabin pressure altitude limits. Based on
the above, the FAA has clearly never specifically required an aural
cabin altitude warning. Although it is recognized 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.In conclusion, this office considers the actions identified in
this letter to be satisfactory in addressing the safety concern.
The existing visual warning system for high cabin altitude is
deemed acceptable. Therefore, the Wichita ACO recommends that
Safety Recommendation 95.401 be closed.
ATSB RESPONSE STATUS: CLOSED-NOT ACCEPTED