Investigation number
199902928
Occurrence date
Location
72 km E Edinburgh, Aero.
Report release date
Report status
Final
Investigation type
Occurrence Investigation
Investigation status
Completed
Aviation occurrence category
Incorrect configuration
Occurrence class
Incident
Highest injury level
None

The Royal Australian Air Force (RAAF) contracted a civilian operator to provide a civil registered Beech 200 Super King Air aircraft, maintenance service, and a check and training service for RAAF aircrew, in accordance with the provisions of the operator's Air Operator's Certificate (AOC).

The flight from Edinburgh, SA, to Oakey, Qld, was conducted as a single-pilot operation. One of the two passengers, who was also a pilot but not qualified to operate the aircraft type, occupied the co-pilot seat. The other passenger was seated in the cabin.

After take-off, as the aircraft climbed through 10,400 ft, the pilot began the 'climb checklist' actions. While performing these checks he received a tracking change instruction from Air Traffic Control (ATC). The passenger in the co-pilot seat noticed that this appeared to temporarily distract the pilot from the checklist as he attempted to reprogram the global positioning system (GPS). The pilot then completed the checklist. During this, the passenger in the co-pilot's seat saw the pilot reposition the engine bleed air switches from the top to the centre positions.

As the aircraft reached the cruise level of FL250, the controller contacted the pilot, indicating that the aircraft was not maintaining the assigned track. The pilot acknowledged this transmission. A short time later the passenger in the co-pilot seat noticed that the pilot was again attempting to program the GPS, and was repeatedly performing the same task. The controller advised the pilot again that the aircraft was still off track, however the pilot did not reply to this transmission. Shortly after this, the pilot lost consciousness.

The passenger in the co-pilot seat took control of the aircraft and commenced an emergency descent. The other passenger then unstowed the pilot's oxygen mask and took several breaths of oxygen from it before fitting it to the unconscious pilot. Neither passenger donned an oxygen mask during the incident.

The controller noticed that the aircraft had conducted an orbit and attempted to contact the pilot, asking him to set the aircraft transponder to 'squawk ident'. The 'ident' signal was received and acknowledged by the controller. The passenger in the co-pilot seat, who had been having some difficulties using the radio, then declared an emergency, indicating that the pilot was incapacitated and that he was conducting an emergency descent.

The controller cleared the aircraft to descend to 5,000 ft and to return to Edinburgh. The clearance was subsequently amended to descend to 6,000 ft due to cloud.

The pilot recovered consciousness during the descent, and once he had regained situational awareness, he noticed that the PASS OXYGEN ON and both BLEED AIR OFF green advisory annunciators were illuminated. These indicators are located on the caution/advisory annunciator panel in the centre instrument sub panel. He also noticed that the engine bleed air switches were selected to the ENVIR OFF position. The pilot reported that he did not see any low cabin pressure warning indications and that the passenger oxygen masks had not deployed.

The pilot then resumed control of the aircraft and carried out an uneventful landing.

Personnel information

The pilot was an experienced RAAF pilot with a civilian flight crew licence, and was qualified to operate the Beech 200 aircraft type. This flight was the first that the pilot had carried out since recently completing type endorsement training.

The passenger in the co-pilot's seat was an experienced RAAF pilot who also held a civilian licence. The passenger in the cabin was an experienced RAAF navigator.

Cabin environment control and oxygen system

The cabin of the Beech 200 was pressurised with environmental air taken from the compressor bleed air outlets of both engines. The bleed air supply was controlled using two three-position switches mounted side by side on the co-pilot's 'environmental' sub-panel. The bleed air switches were of a different shape to most other toggle switches on the instrument panel, which could be discerned by touch. The switches were detented so that they required pulling before changing position (Refer Figure 1).

The switches were placarded bleed-air valve (left and right), and the individual switch positions were (as read from the top selection to the bottom) OPEN, ENVIR OFF, and INSTR & ENVIR OFF. When switched to either the ENVIR OFF or INST AND ENVIR OFF positions, the bleed air valves that controlled the supply of environmental bleed air to the cabin were closed. When switched to the OPEN position, pressurised environmental bleed air flowed to the cabin for air conditioning and pressurisation. The RAAF reported that the switch detents were worn and the switches could be operated without being pulled. The cabin pressurisation controller automatically adjusted an outflow valve in the rear of the cabin to maintain a preset cabin altitude. The pressurisation controller was located on the centre pedestal in the cockpit.

The cabin pressurisation instruments were positioned low on the centre instrument panel, and were partially obscured by the engine and propeller control levers in flight.

The aircraft also had two vent blowers that forced air through underfloor ducts to assist with cabin ventilation. The vent fans were switched on when the aircraft was on the ground to prevent the ducts from overheating. As the aircraft climbed through 10,000ft the aft blower was normally switched off, and the vent blower was normally switched from HI to LOW. The vent fan switches were positioned directly above and below the right bleed air switch on the co-pilot's environmental sub-panel. The switches were of a similar shape to most other toggle switches on the instrument panel, and did not require pulling out of a detent before changing position. The switches were smaller and dissimilar in shape to the nearby bleed air switches.

The sequence of actions detailed in the 'climb checklist' required the pressurisation to be checked before adjusting the air-conditioning and aft blower.

A barometric switch inside the pressure hull of a Beechcraft Super King Air 200, controlled the cabin altitude warning system. The switch was designed to activate when cabin altitude exceeded 12,500 ft. When activated the system illuminated the glareshield mounted left and right flashing red master warning lights and the red ALT WARN annunciator on the master warning panel (refer Figure 2). The master warning lights would remain illuminated until pushed to cancel. The ALT WARN annunciator would extinguish following a decrease in cabin altitude to below 12,500 ft. The aircraft had no aural warning device to warn the pilot of a high cabin altitude. The aircraft type had been certified with the foregoing safety equipment installed.

The passenger in the cabin recalled seeing the ALT WARN caption on the warning annunciator panel on the glareshield at the time of the incident, however, none of the occupants recalled seeing or cancelling the operation of the flashing master warning lights.

The aircraft passenger emergency oxygen system used pressurised dry breathing oxygen. A barometric switch, positioned inside the aircraft's pressure hull, would activate at an internal cabin altitude of 12,500 ft. This activated a system that allowed pressurised oxygen to be directed to the mask retaining door actuators, allowing the doors and masks to drop from the overhead panels. The masks would supply oxygen when the mask was pulled to open a valve. In order to function the system had to be armed by the pilot. An override control enabled the pilot to manually operate the passenger emergency oxygen system in the event of an automatic deployment system failure. Pressurisation of the passenger emergency oxygen system was indicated to the pilot by the illumination of the green PASS OXYGEN ON advisory annunciator positioned on the lower instrument panel area, behind the engine and propeller control levers.

Repealed Australian Civil Aviation Order (CAO) 101.1.5.7, issued on 31 December 1965, stated at paragraph 3.0.4, that:

Aircraft which are normally operated under cruise conditions at flight altitudes in excess of 25,000 feet shall be equipped with a device to provide the flight crew with a warning whenever the cabin pressure altitude exceeds 13,000 feet. The warning should not depend on the reading of a gauge.

Note: An aural warning is strongly recommended.

Australian Civil Aviation Order (CAO) 20.4, paragraph 3, stated that:

Oxygen must be stored, and dispensing and control equipment must be installed, on an aircraft in accordance with section 108.26 of the Civil Aviation Orders.

Australian Civil Aviation Order (CAO) 108.26, paragraph 3.1, which was approved on 14 June 1972, stated that:

An oxygen system for an aircraft which is intended for operations at flight altitudes above 25,000 feet shall include a device to provide the flight crew with a warning whenever the cabin pressure altitude exceeds 14,000 feet.

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

Amendment 92 of this CAO, approved on 7 July 1987, reflected a change in the cabin pressure altitude at which the device should provide a warning. The amended altitude was lowered to 10,000 ft. While the relevant CAOs strongly recommended an aural warning for cabin pressure altitude, fitment was not mandatory.

The Civil Aviation Safety Authority indicated that CAO 108.26 applied to this aircraft.

Hypoxia

The clinical features of acute hypobaric hypoxia include the following:

  • impairment of cognitive skills such as judgement, decision-making, memory, self-regulation and self-awareness;
  • impaired psychomotor coordination and reaction times;
  • restriction of visual field, reduced colour discrimination, reduced auditory acuity and cyanosis; and
  • loss of consciousness, finally resulting in death.

Vision is particularly sensitive to hypoxia. With the onset of hypoxia both the rate and the magnitude of decline in vision are greater than the corresponding decline in hearing. Moderate and severe hypoxia causes a restriction of the visual field, with loss of peripheral vision. 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.

Reading material recommended by CASA for candidates for the Air Transport Pilot Licence theory examinations, since May 1998, included an academic text by Green, Muir, James, Gradwell and Green (1991), that states:

The alerting function for all important failures should be fulfilled by a [sic] audio warning…

Additional research has also indicated that reaction times to visual indications are shorter when supported by an auditory warning signal (Refer to Attachment A).

RAAF aircrew underwent hypobaric chamber training as part of a normal 3-yearly aviation medical refresher training requirement. The pilot and the passenger in the co-pilot's seat had undergone hypobaric chamber training in 1997. The passenger in the cabin had last undergone hypobaric chamber training in 1992. During this training, personnel were expected to learn to recognise and note their individual symptoms of hypoxia through experience. These symptoms could then be used as an aid to indicate the onset of hypoxia.

Both passengers experienced tiredness and slight nausea during the incident. Neither of these symptoms was recognised by the passengers as indicative of the onset of hypoxia. They had not experienced these symptoms during their RAAF hypobaric chamber training.

Global Positioning System

The aircraft was fitted with an Arnav Star 5000 type GPS. The pilot had received no formal training on this particular type of GPS and was unfamiliar with its operation. This was because the unit was due to be replaced with an updated one.

Training

The civil operator's normal endorsement and check and training syllabus was designed to maximise the performance of pilots undertaking regular flying activities in the civilian environment.

This training initially comprised a ground school on the aircraft type. The candidate would then undertake a minimum of two hours of flight training that covered aircraft familiarisation, normal and abnormal procedures. This training satisfied the requirements for an aircraft type endorsement under Civil Aviation Order 40.1.0. The candidate would then undertake a minimum of 25 hours of further flight training with a training captain. During these flights they would undertake normal commercial activities. This meant that not only did the pilot conduct all the mandatory syllabus requirements for the endorsement, but he would also have received the opportunity to reinforce the sequences of actions necessary for normal operations. This would have reduced the potential for human error in these sequences. The candidate would then be assessed with a 'check to line' theory and flight test. The flight test component would comprise a line flight and a base check that would cover normal, abnormal and instrument flight procedures. The company used a memory based 'flow' sequence of actions to ensure that necessary tasks were completed at each stage of normal flight. A pilot would follow a preset sequence of actions, and would then use a scroll type checklist to double-check that tasks had been correctly actioned.

The nature of military flying operations was not the same as civilian flying operations, and therefore military training focussed more on the needs of military tasks. The training syllabus that was developed for the military pilots was different from the normal syllabus used by the civilian contractor, and was originally set to 15 hours flight time. The military flight-training syllabus comprised a larger section of abnormal and emergency procedures. There was less emphasis on conducting training flights that would accurately reflect the type of operations that would normally be conducted.

The RAAF pilots who would normally have been flying this aircraft were mostly test pilots, and the nature of their operations meant that they needed skills and procedures that would allow them to fly a wide range of aircraft. They normally utilised a checklist at the time of actioning each particular task to ensure that they carried out all required procedures.

The flight procedures for the Beech 200 operations utilised the civil operator's checklist system, however the military pilots also developed their own kneepad-mounted checklist that they used at the time tasks were performed. This was in accordance with procedures that they were familiar with. The kneepad-mounted checklist was used with the agreement of the civil operator's chief pilot, so long as the scroll type checklist was still used in the correct manner.

A part of the kneepad-mounted checklist included the 'climb' checks. These were carried out at the transition altitude (10,000 ft) and included the requirement for the pilot to check that the pressurisation was NORMAL, to turn the aft blower fan to OFF, and for the air-conditioning to be adjusted as required.

Aircraft maintenance

Following the incident the contracted maintenance facility checked the operation of the cabin altitude warning system. This check only tested the operation of the warning lights and the continuity of the electrical wiring circuit.

During the incident the aircraft passenger emergency oxygen system activated, but the passenger oxygen masks did not deploy. Maintenance engineers examined the aircraft and found that the centre and rear mask retaining doors had been orientated incorrectly. Consequently, the door-mounted release stops were positioned away from their actuator plungers, and could not be contacted by the door actuators. There was a caution in the maintenance manual that highlighted the consequences of incorrect door fitment. The door retaining lanyards were longer than the initial factory fitment, enabling the doors to be fitted 180 degrees from their correct orientation. One door was correctly oriented, but had not deployed because the door actuator was stiff in operation.

The operation of the passenger oxygen system had last been checked, in accordance with the aircraft owner's system of maintenance, on 11 November 1998. No checks or maintenance had been recorded on the system since that time.

Both barometric switches were removed and tested for correct operation. The switches operated normally with no fault found. The maintenance schedule for the aircraft did not require that the switches be tested for correct operation when installed in the aircraft.

Following the reassembly of the cabin altitude warning system and the passenger oxygen system, the aircraft was test flown in both unpressurised and pressurised modes. All systems operated normally throughout the flight.

The chief pilot carried out a further test flight. During this flight, the pressurisation system was turned off to assess whether the change in cabin pressure was immediately detectable by the occupants. The results of the test indicated that the rate of change of pressurisation started gently, and the occupants did not detect the change until the aircraft cabin altitude had climbed 4,000 to 5,000 ft.

Aircraft Details
Manufacturer
Raytheon Aircraft Company
Model
200
Registration
VH-OYA
Operation type
Military
Sector
Turboprop
Departure point
Edinburgh, SA
Destination
Oakey, Qld
Damage
Nil