A Boeing 747-400 (B747-400) was en route from Singapore to Sydney at flight level (FL) 330 on air route A585, and a B747 was tracking in the opposite direction at FL350 from Melbourne to Jakarta on air route G222. The routes A585 and G222 converged at SAPDA, a position approximately 720 NM north-west of Broome on the boundary of the Australian and Indonesian flight information regions (FIRs). Route G222 was north-east of route A585 and the prescribed lateral separation point between the routes was 272 NM south-east of SAPDA. The aircraft were under the control of the Kimberley sector controller of the Brisbane centre.

The B747-400 was estimating SAPDA at 1811 Universal Coordinated Time and the controller approved that crew at 1747 to climb to FL350 at SAPDA. The Kimberley controller was advised at 1806 the B747 was at METUM, a position 252 NM south-east of SAPDA, at 1805 maintaining FL350 and estimating SAPDA at 1836. At 1812, the Kimberley controller received a SAPDA position report from the B747-400 crew and shortly after recognised there was no separation being applied between the aircraft. At 1813, the Kimberley controller instructed the B747-400 crew to descend to FL330, however there was an infringement of separation standards. The B747-400 crew subsequently reported maintaining FL330 at 1819.

The estimated time of passing of the aircraft was 1824. The Kimberley controller needed to establish the vertical separation standard of 2,000 ft between the aircraft before 1809 to ensure separation.

The Kimberley sector was a procedural sector operated by a single controller. Communication between controllers and flight crews could be by either:
- very high frequency (VHF) radio,
- controller pilot data link communication (CPDLC), or
- high frequency (HF) radio through a third-party radio operator.

The controller was communicating with the B747-400 crew using CPDLC and with the B747 crew by third-party HF radio. There was no VHF radio coverage in the portion of the sector in which the aircraft were operating.

The controller commenced the shift at 1300 (2300 Eastern Standard Time) and worked till about 1530 when he had a break. He returned to the position at 1610 and remained there until the occurrence. Normally during the period from 1400 to 1800, the number of aircraft in the sector gradually increased and after that time, traffic numbers decreased. The controller reported that there had been a busy period that had finished just before the occurrence. That was the controller's first shift following a 2-day break.

When the B747-400 crew requested approval to climb to FL350 via CPDLC, the controller checked for conflicting aircraft on the air situation display. At that stage, the B747 on G222 was over Western Australia and the controller reported that he might have perceived that aircraft as part of a group of aircraft on a more northerly route. Consequently, he coordinated a change of level with the adjacent Indonesian sector controller, and then instructed the B747-400 crew to climb at SAPDA.

The air traffic system had a flight plan conflict probe (FPCP) function to assist in the early identification of conflicts outside radar coverage. However, the FPCP had not been included in the commissioning of the new air traffic control system during 1998-99 and was not active.

Sequence of events

The Cessna A152 Aerobat aircraft was engaged on an aerobatics training flight with the pilot the sole occupant of the aircraft. The pilot was practising for an aerobatic competition and had been having problems conducting stall turn manoeuvres.

Before the accident flight, the pilot had completed an aerobatic practice flight with an instructor. The pilot then decided to fly a solo flight to practise stall turns without the effect of a second person's weight on aircraft performance in aerobatic manoeuvres. He then intended to practise his full aerobatic sequence, which the instructor later stated was well within the pilot's capabilities. Between flights the pilot refuelled the aircraft and consumed a bottle of soft drink.

After takeoff for the solo flight, the pilot discussed with his instructor by radio, his intentions for the flight and the criticisms of his manoeuvres during the dual flight. The instructor later reported that during the discussion, everything concerning the pilot and the aircraft seemed normal.

Witnesses some distance away heard the aircraft fly over. They later heard a thump and noticed smoke rising from the same direction as the source of the sound. There were no witnesses to the impact.

Wreckage examination

The wreckage was contained within a relatively small area, apart from two sections of fuel tank and the associated wing that were found about 40 m away. Most of the aircraft had been consumed by a post-impact fire.

Examination of the accident site revealed that the aircraft had impacted the ground in balanced flight at high speed in an attitude of approximately 70 degrees nose down. The engine was producing high power at impact. Examination of the wreckage did not reveal any technical defect that would have contributed to the accident.

Pilot

The pilot was 61 years of age and had been flying since 1979. He held a Private Pilot Licence (Aeroplane), and a valid Class 2 medical certificate. He had accrued a total of 893.3 hours flying experience, including 7 hours in the last 90 days, probably all on type. In the last 30 days, he had flown 1.3 hours, all on the day of the accident. Since 1982, the pilot's principal interest had been aerobatics, and in recent years he had become involved in competition aerobatic flying. Since November 1994, he had held a CASA approval to conduct aerobatics down to 1,500 ft AGL. He had completed his most recent biennial flight review on 26 June 2000.

The pilot had a long history of hiatus hernia and taken medication for it but had not undergone surgery. At the time of the accident, he was not taking prescribed medication. For about 10 years, he had been prone to fits of coughing after eating and drinking. During these attacks, his ability to perform other tasks was impaired. About 45 minutes before the dual flight, the pilot had eaten a burger and chips. During the dual flight, he had suffered a fit of coughing during which time his attention to flying the aircraft was reduced.

Toxicological examination of the pilot revealed the presence of the drug doxylamine, at a concentration of 4.7 mg/kg in the liver. The finding was reported as `semiquantitative' with a possible error of 20 percent. However, regardless of any error, the pathologist regarded the concentration as sufficiently high to possibly affect the pilot's ability to fly the aircraft.

Medical information revealed that makers of pharmaceutical products usually include doxylamine with other agents such as paracetamol and codeine in strong analgesic medication for such conditions as migraine. In isolation, doxylamine is classified as an anti-histamine, but it has strong anti-emetic properties useful for treating motion sickness, nausea and similar conditions. It is also a drying agent used in a number of non-prescription cold and flu preparations. However, either alone or in conjunction with other substances, doxylamine can cause drowsiness, visual disturbance and can contribute to disorientation.

Two Grob G115-C aircraft, VH-ZIR and VH-ZIB collided at low altitude while on short-final approach to runway 18 at Merredin WA. Each aircraft was being flown by a student pilot on a solo training exercise and was being operated under visual flight rules.

Several witnesses had sighted the two aircraft as they converged on short final. They recalled that the lower aircraft was closest to the runway threshold, but was being approached from above and behind by the second aircraft, which was travelling slightly faster. One of the witnesses, a pilot in a taxiing aircraft, made a broadcast on the aerodrome's Common Traffic Advisory Frequency (CTAF) for the aircraft on final to `go around'. Moments later the two aircraft collided. The collision occurred in the vicinity of the runway threshold and at a height that was estimated to be less than 50 ft.

Neither pilot was able to maintain control of their aircraft following the collision. The nose of ZIR pitched steeply upwards and the aircraft became inverted before it impacted the runway. The nose of ZIB pitched downwards and the aircraft landed heavily nose first. Both aircraft came to rest on the runway. The pilot of ZIR received minor injuries and was trapped in the cockpit until bystanders lifted the wreckage and helped him clear. The pilot of ZIB was not injured.

Although the investigation could not positively determine the sequence of impact between the two aircraft, the physical evidence was consistent with ZIR being initially struck from above and behind by ZIB. The lower rear-right fuselage of ZIR sustained several propeller strikes. There was additional evidence of secondary contact between the two aircraft as ZIR became inverted and prior to impacting the ground. The VHF radios in both aircraft were tuned to the CTAF frequency and the altimeters were set to a QNH of 1022 hPa.

Merredin is a privately owned, non-controlled aerodrome. It is operated by a Jandakot-based flying training organisation and was used as a satellite aerodrome to supplement training operations. The weather conditions at the time of the accident were described as generally fine, with good visibility and a 20-25 kts southerly wind.

The pilot of ZIB had recently transferred to Merredin after completing his early ab-initio training at Jandakot (a General Aviation Aerodrome Procedures controlled aerodrome). Since arriving at Merredin he had completed 1.9 hours of dual circuit training and an additional 2.8 hours of dual flying in the local training area. The student was described as an above average student who displayed a good level of situational awareness for his level of experience. The accident occurred during the student's first solo flight at a non-controlled aerodrome.

The pilot of ZIR was reported to be an above average student and had completed most of his flying at Merredin. The accident occurred at the end of his first solo cross-country navigation exercise.

The pilot of ZIR had joined the circuit crosswind as the pilot of ZIB had lined up for take-off on runway 18. Although the pilot of ZIB was aware there was circuit traffic ahead, he did not see the aircraft at any stage. When his aircraft bounced during the first landing attempt, the pilot of ZIR discontinued the approach and broadcast on the CTAF that he was going around. The pilot of ZIB completed his first touch and go without incident. He did not hear the transmission from the pilot of ZIR, indicating that he had gone around, and assumed that the aircraft had already landed.

On the second circuit, the pilot of ZIR broadcast his position downwind. The pilot of ZIB recalled that he was turning crosswind when he heard this broadcast and realised that there was an aircraft ahead. In turn, he broadcast his position downwind and received no response to his transmission. Although he could not see the aircraft he was following, the pilot of ZIB surmised that this situation was similar to his first circuit and concluded that the other pilot was probably not making his downwind broadcasts in the standard position. The pilot of ZIR subsequently recalled that his second circuit was slightly wider than normal.

The pilot of ZIR recalled that he heard the downwind broadcast from the other pilot and had noticed that this call was made shortly after he had made his transmission. He assumed that the other aircraft was behind him and would follow him in the circuit.

Neither pilot sighted the other aircraft at any stage during downwind, base or final legs of the circuit. Both pilots were conforming to the standard oval circuit pattern recently introduced by the training organisation. That procedure involved a climbing turn from 500 ft above ground level (AGL) on the upwind leg to position the aircraft downwind at 1,000 ft AGL. The base turn was commenced 30 seconds after the aircraft had passed abeam the landing threshold and consisted of a descending turn onto final approach.

Darwin air traffic control was using runway 29 as the primary runway. Two BAe Hawk aircraft were approved to depart in the opposite direction from runway 11. A Cessna 310 (C310) had departed from runway 29 prior to the Hawks and was climbing through 3,500 ft while tracking on the 107 radial of the Darwin VOR navigation aid.

The planner controller had coordinated the clearance from runway 11 with the approach controller, who was performing both the departure and approach control functions. However, the flight strip indicated that the Hawks would depart from runway 29. As the aircraft became airborne the error was detected, but the pair were quickly closing on the C310. Traffic information was not passed to any of the crews and the aircraft came within 1.5NM of each before the Hawks had established themselves 1,000 ft above the altitude of the C310. There was an infringement of separation standards, which required a minimum of 3 NM horizontally or 1,000 ft vertically.

The investigation revealed that the planner controller had carried out the correct coordination but had incorrectly written runway 29 on the flight strip for the Hawks. When the aerodrome controller coordinated the correct information to the approach controller (using the phraseology "next runway one one"), the approach controller was not alerted by the words "one one". Consequently, the approach controller issued an instruction for the Hawks to depart on runway heading still believing them to be using runway 29.

When the pilots of the Hawks made radio contact with the approach controller after departure, the controller chose to not initiate evasive action as the rate of climb of the Hawks was far greater than that of the C310, and they had already reached the altitude of the C310. This decision was taken at a time when the horizontal separation had reduced to less than the 3 NM standard. The controller believed that the time taken to issue, and have the pilots respond to, a turn instruction would take longer to attain a horizontal standard than allowing the climb to continue until the vertical standard was achieved.

History of the flight

The pilot had submitted a flight plan nominating a charter category, single pilot, Instrument Flight Rules flight, from Darwin to Port Keats and return. The Piper Aerostar 600A aircraft, with 6 Passengers on board, departed Darwin at 2014 Central Standard Time and arrived at Port Keats at 2106 hours after an uneventful flight. The passengers disembarked at Port Keats and the pilot prepared to return to Darwin alone. At 2119 hours the pilot reported taxying for runway 34 to Brisbane Flight Service. That was the last radio contact with the aircraft. Witnesses noted nothing unusual as the aircraft taxied and then took off from runway 34. As a departure report was not received, a distress phase was declared and subsequently a search was instigated.

The following morning a number of major structural components of the aircraft, including the outer left wing, were located at a position 24 km north-east of Port Keats aerodrome and close to the aircraft's flight planned track. The main portion of wreckage was found four days later, destroyed by ground impact. The impact crater was located a considerable distance from the previously located structural components and indicated that an inflight breakup had occurred. The accident was not survivable.

Wreckage examination

A portion of the left wing, part of the left aileron, the cargo door, a 1.3 metre section of the left horizontal stabiliser and the right landing gear door skin were found remote from the main impact area. The section of left wing had separated outboard of the engine nacelle. All fracture surfaces and tear lines on the wing section and the aileron were consistent with overload failure. No evidence of pre-existing deficiency such as fatigue fracture or corrosion was found.

The main body of the aircraft impacted the ground in a steep, nose down, approximately wings level attitude with substantial forward velocity on a generally southeasterly heading. Damage to the structure was extreme with very little fuselage intact and severe compression crush damage to the fuselage and wing structures. There was no evidence of fire in the aircraft or its components.

All control surfaces were found. Examination of the flight control continuity was not possible due to the extent of the aircraft damage. The flaps were found in the stowed position on both wings. All landing gear components were found outside the impact crater, indicating that the landing gear may have been extended at the time of impact. Recovery of the right main landing gear door skin remote from the main wreckage area was consistent with the gear being extended in flight. The engines and propellers remained attached to the airframe and were found at a depth of 1.5 metres and exhibited indications of low power settings at impact. No pre-existing damage to the engines was evident. The engine-driven vacuum pumps were examined and there was no evidence of abnormal operation or failure of the pumps prior to impact.

Damage to the cockpit, flight and engine controls, instruments and switches was extensive. It was not possible to determine the selected position of controls and switches. Both attitude indicators were recovered and examination determined that they had both been operating at impact and indicated the same steep pitch attitude of 65-70 degrees nose down. That pitch attitude corresponded with observations at the accident site where the inclination between the crater and the damaged foliage was measured at approximately 60 degrees. Rotational scoring on the gyro mechanisms and similarities in indicated pitch attitudes suggested that the attitude indicators were most likely operating normally at impact.

The aircraft had a valid Maintenance Release and there was no maintenance outstanding at the time of the accident. The investigation found no evidence to suggest that the aircraft was not serviceable at the time of the accident.

Reconstruction of the flight

Calculations based on the aircraft's performance charts determined that if the flight had progressed normally to a point overhead the general location of the wreckage, the aircraft should have been close to its flight planned cruise altitude of 10,000 ft. Trajectory analysis of the wreckage distribution determined that the aircraft broke up between 2,700 and 4,000 ft.

The aircraft was equipped with a serviceable autopilot. However, a colleague who had flown with the pilot reported that the pilot's routine was to leave the autopilot disengaged until the aircraft was established in the cruise.

Pilot information

The pilot was aged 68 and the holder of a Commercial Pilot Licence endorsed for the Piper Aerostar 600A aircraft. The licence contained endorsement limitations that vision correction was required and the licence was not valid for operations requiring an Airline Transport Pilot Licence. The pilot held a valid Command Instrument Rating and had passed a renewal test on 25 July 2000. He had a total flying experience in excess of 15,000 hours of which 122 were in the Aerostar. Colleagues commented on his very professional and careful approach to flying, describing him as meticulous when it came to safety. His total flight time in the previous 30 days was 13.1 hours of which 3.5 hours were at night (including the accident flight). His most recent flight prior to the day of the accident was 2 days earlier in a Piper PA-31 aircraft. It had been 16 days since he had flown the Aerostar. The pilot held a Class 1 Medical Certificate valid until 13 October 2000. His last flight crew medical examination on 13 October 1999 revealed no deficiencies other than the continuing requirement to wear prescription lenses.

Examination of the pilot's medical history revealed that in 1990 the pilot's risk factors for ischaemic heart disease required that he undertake additional tests and monitoring. He was also placed on medication for a raised serum lipid (high Cholesterol). Specialist medical assessment found that while that condition was not considered to be critical, the combination of age, raised serum lipid and abnormal Stress Electrocardiogram increased the possibility of coronary ischaemia developing with time. No autopsy was able to be conducted.

Witnesses described the pilot as apparently healthy and in good spirits on the day of the accident. The pilot was semi-retired and he generally had a relaxed lifestyle. Enquiries revealed that his normal sleep pattern was approximately 10:00 pm to 6:00 am and that he slept well. In the 2 weeks prior to the accident most of his time was spent renovating the boat on which he resided. He showed no signs of fatigue, illness or injury. At the time of the accident he had been on duty for approximately 4 hours.

Meteorological information, terrain features and visual clues

An analysis of the meteorological conditions in the vicinity of the crash site at 2125 hours indicated that there was no significant weather. Light wind and clear skies were observed and there was no indication of turbulence. One of the passengers on the outward journey remarked that that it was a smooth flight. Moon data for that evening indicated a waxing crescent with approximately 20 percent of the moon's visible disc illuminated. At the time of the accident the moon was 13.2 degrees above the horizon at an azimuth of 265.3 degrees. The aircraft's flight planned track was 037 degrees and therefore flying away from the moon. Local witnesses reported the night as being very dark.

The area directly north of Port Keats aerodrome had few prominent features apart from a small settlement that was vacant at the time of the accident and was therefore probably unlit. During the climb to cruise the natural horizon would have been obscured or nonexistent. The view outside the cockpit in the prevailing conditions of good visibility (in the meteorological sense) would have been close to total darkness.

Manoeuvring limits

The operating limitations section in the Flight Manual for the aircraft specified a maximum manoeuvring speed of 162 kts Indicated Air Speed (IAS). At that speed, the aircraft's structure was designed to withstand full symmetrical deflection of the flight controls. That maximum safe manoeuvring speed decreased as the aeroplane gross weight was reduced. The manoeuvring speed at the estimated weight of the aircraft at the time of the accident was calculated to have been 148 kts IAS. Allowing for a design safety factor of 1.5, the ultimate load limit would have been exceeded at 181 kts IAS with a full, abrupt movement of the controls. The normal cruise speed of the Aerostar was approximately 170 knots IAS and 200 knots IAS was easily attainable in a cruise descent. Abrupt control movements at any given airspeed can cause peak loads significantly higher than those produced by steady inputs. A rapid and large application of aileron control input at high speed in a dive could produce torsional loading in a wing in excess of the design strength. That loading could result in wing structural failure consistent with the failure observed to the left wing.

Spiral instability

The Aerostar exhibits weak spiral stability. If, for example, the pilot becomes distracted while hand flying the aircraft on instruments, the aircraft may start to turn. The initial turning tendency is usually small and difficult to detect, especially if the pilot is not concentrating on instrument scanning. The nose of the aircraft will drop, a spiral descent commences and the speed will rapidly increase. Although the onset of a spiral dive is usually insidious, with physiological clues not strong enough to alert a distracted pilot, a well-developed spiral can rapidly develop. Airspeed can quickly increase to the point where there is much greater potential of exceeding the design G-loads. When denied strong visual cues, inadvertent entry to a spiral dive can happen even to highly experienced pilots. A pilot, confronted with a high-speed spiral, is trained to slow the buildup of airspeed, roll the aircraft to a wings-level attitude and then recover from the dive. The first step would therefore be to ensure the throttles are closed. Additional slowing, in aircraft like the Aerostar, can be achieved by lowering the landing gear and moving the propeller controls to a high RPM setting.

Human Physiology

Spatial disorientation is a situation in which a pilot fails to sense correctly the position, motion or attitude of the aircraft. It results from conflicting information from the pilot's senses, primarily those of vision and balance. Alternatively, where there are insufficient visual cues, the information from the sense of balance is all that is available to determine orientation. The sense of balance is extremely unreliable and, depending on the circumstances of the flight, may provide erroneous information to the pilot. If there is no visual means with which to crosscheck the information from the balance senses, the pilot may be unaware that it is in error. A pilot's perception of the aircraft's orientation in space may thus be incorrect, and the pilot will not be aware that this is so.

Fatigue can result in a number of potentially significant performance decrements including increased reaction time, lowered arousal, increased susceptibility to distraction, poor self monitoring, and reversion to previously well learned skills.

The Embraer Brasilia aircraft was being operated on a Regular Public Transport flight from Dili, East Timor to Darwin NT and was levelling off to cruise at Flight Level (FL) 210.

Shortly after, and when the aircraft was approximately 90 NM SW of Dili, the flight crew realised that the cabin air pressure was changing. The change was confirmed by reference to the cabin altitude and cabin rate of climb indicators. The cabin altitude was rising at an increasing rate, with the rate of increase quickly exceeding the instrument's full-scale deflection of 2,000 ft/minute.

The crew immediately commenced a high-speed descent and, because they were reacting to the increasing cabin altitude ahead of the aircraft's warning systems, did not don the supplemental oxygen masks. The aircraft was descending at a rate of 3,000 ft/min. While on descent, the crew continued to monitor the cabin altitude indicator.

As the cabin altitude exceeded 10,000 ft, the aircraft master caution warning and the cabin altitude warning chimes activated. At that stage, the aircraft was passing FL140 and continuing to descend at about 3,000 ft/min. With approximately one minute remaining before reaching 10,000 ft, the crew again decided against using the supplemental oxygen masks.

The crew continued the descent and appeared to regain some control of the cabin altitude by using the cabin pressurisation controller in the "manual" mode which maintained a cabin altitude of approximately 8,000 ft. They levelled the aircraft at FL112, the lowest safe altitude for this route segment, and continued to their planned destination. The flight attendant informed the pilots that during the descent the supplemental oxygen masks in the main cabin had automatically deployed.

No injuries were reported as a result of the incident.

Maintenance staff inspected the aircraft and replaced the pressurisation controller. The pressurisation system performed normally on the next scheduled flight. However, on the following sector, the system again malfunctioned. ATSB investigation report BO/200003725 refers.

Flight data recorder

Analysis of the flight data recorder indicated that the aircraft reached top of climb at 0930 UTC (Coordinated universal time) and was maintaining FL 210. At 0944, the aircraft began to descend. The descent profile indicated that the descent was conducted at a rate of about 2,100 ft/min. At 0949, the aircraft levelled off at FL113.

Cabin altitude warning system

The aircraft was equipped with a cabin altitude warning system. In the event of the cabin altitude exceeding 10,000 ft, a 3 chime aural alert and a voice "cabin" warning sounded. In addition, a red "cabin alt" warning light would illuminate on the main annunciator panel and the red "master warning" light would flash. The system activated as designed.

Supplemental oxygen system

A supplemental oxygen system was installed for use by the crew and passengers in the event of a failure of the cabin pressurisation system. It was a conventional high-pressure gaseous storage system, which distributed low-pressure oxygen to the crew and passenger breathing masks. The passenger masks were stored in overhead dispensing units. The supplemental oxygen system operated normally and the masks automatically deployed when the cabin altitude exceeded 14,000 ft.

Hypoxia

Hypoxia describes the physiological condition where insufficient oxygen is available to meet the needs of the body. The condition is particularly significant because of the rapid rate at which symptoms can manifest themselves and the variation in the onset of symptoms between individuals. A person suffering the effects of hypoxia could experience a range of symptoms capable of adversely affecting their ability to safely operate an aircraft. These symptoms include impairment of mental performance, loss of judgement, vision impairment, memory loss, reduced levels of awareness and muscular impairment.

The effects of hypoxia may be such that the person is unable to recognise the symptoms or identify that their level of performance has been impaired.

Individuals experiencing the effects of hypoxia can have difficulty in completing even simple tasks. The severity of these symptoms depends on many factors, including the altitude to which the individual is exposed, the duration of the exposure and individual physiological differences. Untreated, hypoxia can result in loss of consciousness and death.

Depressurisation events and response procedures

The US Federal Aviation Authority Civil Aeromedical Institute (CAMI) classified any occurrence of decompression as significant if the cabin altitude exceeded 14,000 ft, the cabin masks were deployed, or if the occurrence resulted in injuries. The incident satisfied two of those criteria.

A rapid depressurisation, as defined by CAMI, occurs when the cabin altitude increases by more than 7,000 ft/min. There was no evidence that during the incident the change in cabin altitude exceeded that rate.

The crew had planned to cruise at FL210. For flights in "pressurised aircraft engaged in flights not above FL250", the Civil Aviation Safety Authority required that supplemental oxygen be used by all flight deck crew "at all times during which the cabin altitude exceeds 10,000 ft". "A crew member (not being a flight crew member on flight deck duty) ... must use supplemental oxygen at all times during which the cabin pressure altitude exceeds Flight Level 140." CAO 20.4 refers.

The aircraft must also carry sufficient supplemental oxygen for passengers as specified in CAO 20.4 Subsection 7.5.

"Supplemental oxygen for passengers

7.5 A pressurised aircraft to which this subsection applies that is to be operated above 10,000 feet flight altitude must carry sufficient supplemental oxygen:

(a) where the aircraft can safely descend to Flight Level 140 or a lower level within 4 minutes at all points along the planned route and maintain Flight Level 140 or a lower level for the remainder of the flight - to provide 10% of the passengers with supplemental oxygen for 30 minutes or 20% of the passengers with supplemental oxygen for 15 minutes; and

(b) where the aircraft cannot safely descend to, or maintain, Flight Level 140 or a lower level in accordance with subparagraph (a) - to provide each passenger with supplemental oxygen for so much of the flight time above Flight Level 140 that exceeds 4 minutes duration and to provide 10% of the passengers with supplemental oxygen for 30 minutes or 20% of the passengers with supplemental oxygen for 15 minutes."

The Quick Reference Handbook (QRH) used by the crew included a checklist for use following an illumination of the cabin altitude warning light. That checklist did not include a requirement for the crew to don oxygen masks but contained checklist items to establish control of the cabin pressure utilising the manual pressurisation controller. The QRH also included a checklist for rapid depressurisation that required the crew to immediately don oxygen masks and commence an emergency descent.

The Boeing 737 was conducting a night VOR/DME approach to runway 05 at Adelaide Airport, which was under the influence of a low-level weather trough moving through the area. The co-pilot was the handling pilot.

The crew had reviewed the approach procedure and noted that due to strong northerly winds on the final approach track of 035 degrees, their expectation of sighting runway 05 through the co-pilot's window would be enhanced. At about 600 ft above ground level (AGL), the aircraft descended below the cloud base into an area of poor visibility. The crew observed lights through the co-pilot's window which they believed to be on the aerodrome. They discontinued the instrument approach and tracked towards the lights, continuing to descend.

As the aircraft approached the lights, the pilot in command asked the co-pilot if he could see the runway precision approach path indicator (PAPI). The co-pilot replied that he could not. The pilot in command then checked his electronic horizontal situation indicator, which was operating in the VOR mode, and noted that the aircraft was well to the right of the inbound track of the approach. By this time, the aircraft had descended to 320 ft radar altitude. The crew immediately initiated a missed approach and obtained a clearance for an instrument landing system (ILS) approach to runway 23. The aircraft subsequently landed safely with a 6 kt downwind component.

At its minimum altitude, the aircraft had deviated 0.4 NM to the right of the runway centreline, at a distance of 1.1 NM from the runway threshold. The lights towards which the aircraft was tracking were south of the airport, probably on the Anzac Highway.

In the prevailing conditions of darkness and poor visibility, the crew's actions were consistent with an "error of expectancy". Such an error can occur when a person expects to perceive certain environmental cues and the strength of that expectation leads the person to misinterpret the environment, believing that those cues are present. In this case, the crew expected to see a lighted line feature aligned in a north-easterly direction through the co-pilot's window. What they saw fitted with their "mental model" of what they expected to see. At that point, the "real world" became more psychologically compelling than the information from the navigation instruments.

Expectancy is an unconscious phenomenon that is very difficult to overcome. Generally, it is more worthwhile to modify the environment or the task that led to the error, than to simply encourage people not to make such errors. Aircraft flying the final approach path of the runway 05 VOR/DME procedure, approach the aerodrome inbound along a track of 035 degrees M (south of the extended runway centreline). Aircraft do not intercept the extended centreline until the missed approach point at 1.5 NM by DME. Further, there are no approach lights for runway 05. Consequently, there are few visual cues to assist crews to intercept the extended runway centreline in darkness and/or poor visibility. Conversely, the nearby Anzac Highway is a prominent lighted line feature that can draw the crew's attention.

Other examples of crews misidentifying ground features for runways are:

16 June 1988, Airbus A300, Perth WA
The crew carried out a night VOR/DME approach for runway 03. The cloud base was 800 ft. After the aircraft entered visual conditions, the crew were unable to visually identify the runway, which was not equipped with approach lighting. The crew had been confused by other ground lighting.

14 May 1989, Boeing 737, near Mackay Qld
The crew misidentified Broadsound Road for runway 14. The aircraft descended to 170 ft AGL on final approach before the crew became aware of the error.

In both of the above occurrences the crews carried out missed approaches after realising their errors.

Gladstone Qld
Four respondents to a survey conducted by the Bureau of Air Safety Investigation in 1997 to obtain data for the Regional Airlines Safety Study, reported that the bright lights illuminating a railway marshalling yard adjacent to the final track for runway 10 could "drown out" the runway lights and create the illusion of a false runway.