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Safety Action

Summary

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

 
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