The Boeing 767 had just reached cruise altitude at flight level 330 approximately 40 minutes out of Singapore enroute to Perth, when the flight crew noted smoke and electrical fumes on the flight deck. The source of the smoke and fumes could not be readily identified. The pilot in command elected to have the flight crew don oxygen masks, and diverted to Jakarta.

The operator's engineering personnel examined the aircraft and found the right DME (Distance Measuring Equipment) circuit breaker open. Technicians isolated the problem to the right DME interrogator unit. The malfunctioning DME unit was disabled in accordance with the MEL (Minimum Equipment List) guidelines to allow the aircraft to continue to Perth. Following arrival in Perth, the unit was replaced.

Examination of the unit by the manufacturer revealed that the DME unit's A5 modulator had overheated. This failure mode was similar to two other units, which had overheated on a different aircraft in January 2000 (see Occurrence 200000055). The failure mode of those units was such that the A5 modulator had overloaded the positive 86 volt DC power supply and overheated the power transformer. Compliance with service bulletins recommending product improvements to this unit were not mandatory, and the recommended modifications had not been incorporated into this unit, or the previous two units that had sustained failures.

The Embraer Brasilia aircraft was being operated on a Regular Public Transport flight from Dili, East Timor to Darwin NT. Shortly after the aircraft had levelled off at FL230, the pilot in command became aware of cabin air pressure changes. That was verified by reference to the cabin rate of climb indicator, which indicated that the cabin altitude was increasing at a rate of approximately 500 ft/min.

The crew reported that they attempted to regain control of the cabin pressurisation system by switching from the automatic to the manual pressurisation controller. When that action did not rectify the problem, the crew immediately commenced a descent. The rate at which the cabin altitude was increasing was not excessive and the crew elected to perform a normal descent. While on descent, the cabin altitude rate of climb suddenly increased to about 1,000 ft/min. The rate of pressure loss was not uncomfortable and the aircraft was rapidly approaching FL140. The crew did not don supplemental oxygen masks during the initial descent.

The flight attendant was at the rear of the aircraft when the passenger oxygen masks deployed. At almost the same time the interphone sounded and she moved to the front of the aircraft to answer the call (there was no cabin interphone at the rear of the aircraft). The flight attendant did not use any of the spare passenger masks as she moved forward through the cabin and did not don her mask after arriving at her crew station. The pilot in command advised her that there was a slight depressurisation problem and that they had commenced a descent to 10,000 ft. The pilot warned her that the passenger masks may deploy and she advised him that they already had. The flight attendant was then instructed to get the Emergency Procedures card and perform the emergency briefing. The flight crew were not wearing supplemental oxygen masks when she spoke to them at that stage of the descent.

The crew reported that they donned oxygen masks later during the descent after the passenger oxygen masks automatically deployed. The flight attendant did not don a mask at any stage of the descent. She reported that some passengers also did not use the masks after they deployed, or after being instructed to do so during the emergency briefing.

The crew established the aircraft in visual meteorological conditions, with fine weather forecast for the planned route. The aircraft landed with about 1,100 lb of fuel, which was within the standard company reserves for depressurised operations. No injuries were reported as a result of the incident.

The aircraft sustained a similar pressurisation problem 12 hours earlier. Following that incident maintenance crews replaced the pressurisation controller and returned the aircraft to service. The aircraft then completed one sector without incident.

In response to the second occurrence, the rear cargo compartment door seal was inspected and found dislodged from its retaining rail. The damage was assessed to have most likely occurred during the loading and unloading of passenger baggage and freight.

After reinstallation of the door seal in the retaining rail, the aircraft was test flown and returned to service without re-occurrence.

Recorded information

Analysis of the flight data recorder indicated that the aircraft reached top of climb (FL231) at about 2347 UTC (Coordinated universal time) and almost immediately commenced a descent. The recording indicated that the descent was conducted at a rate of approximately 2,600 ft/min and that the aircraft reached FL140 at 2351. The aircraft maintained that altitude for approximately 5 minutes before continuing a 500 ft/minute descent to maintain a cruise altitude of 10,000 ft.

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 would sound. 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 flight crew masks were of the quick donning type. The passenger masks were stored in overhead dispensing units positioned in the ceiling of the passenger cabin. An altimetric switch ensured automatic deployment of the oxygen masks whenever the cabin altitude exceeded 14,000 ft. Manual deployment of the masks could also be performed from the cockpit. The supplemental oxygen system operated normally during the incident flight 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. Those 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 those symptoms depends upon 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 occurrence satisfied two of those criteria.

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

The crew had planned to cruise at FL230. 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 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.

During the descent, the aircraft cabin altitude exceeded 14,000 ft and the passenger oxygen masks automatically deployed. It was not possible to estimate the maximum cabin altitude experienced, nor the length of time that the cabin altitude exceeded 10,000 ft. The passenger oxygen masks probably deployed during the first 4 minutes of the descent from FL 230.

After establishing the Piper Chieftain in the cruise, the pilot occupying the right seat commenced a daily trend monitor of the engine operating parameters. During this procedure, the right engine oil pressure was observed to be low. While monitoring the oil pressure, the pilot noticed the right engine oil pressure decreasing accompanied by an increase in engine oil temperature. Shortly after, oil was observed trailing from the engine nacelle vent and skin joints. The right propeller was feathered and the engine shut down.

Inspection by a maintenance engineer found that the No. 3 piston had sustained detonation damage. The piston and cylinder were changed and the aircraft cleared for a ferry flight to Jandakot to facilitate a bulk strip inspection of the engine carried out under ATSB supervision. During this inspection further evidence of heat stress was found necessitating shipment of the affected components to the ATSB for a more in-depth examination. The components inspected exhibited the typical effects of over-temperature operation. Evidence of detonative combustion was also noted within other cylinders of the engine.

The fuel injection unit was examined and its functions tested on an approved component test bench. The unit was found to control fuel/air mixture within normal limits without fault and the automatic functions of the unit would not have induced processes that lead to detonation.

The company's technique for leaning the engines in cruise routinely allowed the exhaust gas temperature to exceed the maximum permissible temperature for a short period of time, and set the temperature at a higher level than would have been achieved by following the aircraft manufacturer's procedures for leaning the engines.

The right engine of a Piper Chieftain will normally run at a higher temperature than the left because of factors such as the counter rotation of the propeller inducing different cooling airflow, and the presence of an air-conditioning compressor in the front intake area obstructing airflow. This aircraft was only fitted with one cylinder head temperature (CHT) probe and one exhaust gas temperature (EGT) probe per engine. The installation has the number 6 cylinder instrumented for CHT and a single EGT probe monitoring a combined gas stream. It would not be possible to determine from the cockpit indications if any of the remaining five cylinders of the engine were operating at or beyond the CHT and EGT indicated to the pilot.

The company practice of leaning to peak EGT exceeded the pilot's operating handbook recommendation of a maximum of 1650 degrees F EGT. Exceeding the maximum permissible EGT on a regular basis, and sustained operations at or very near peak EGT at the manifold air pressure and engine revolutions per minute set as company policy, most probably put one or more of the operating cylinders into the detonation regime. This would have produced the heat stress and contributed to the loss of material strength of components evident within this engine.

The pilot of an Instrument Flight Rules (IFR) CT4 Air trainer made an inbound report on the Armidale common traffic advisory frequency (CTAF) when at 8 NM southwest of the aerodrome. Four minutes later the pilot broadcast that he was overhead, with the intention of conducting an NDB/DME approach to runway 05.

Subsequently, an IFR Beech 1900 taxied at Armidale for departure from runway 05. Both aircraft had been given traffic information on each other by Brisbane air traffic services. When the Beech 1900 crew broadcast that they were taxiing, the CT4 pilot advised that he was about to turn inbound on the sector 1 entry for the runway 05 NDB/DME procedure and was maintaining 5,800 ft.

The Beech 1900 crew acknowledged the call. The CT4 pilot then awaited the lining up or rolling call from the Beech 1900 crew so that they could arrange mutual separation.

After completing the inbound turn the CT4 had approximately 2 NM to run on the inbound leg of the sector 1 entry. At that stage the pilot observed a Traffic Collision Alert Device (TCAD) indication that an aircraft was 1,100 ft below, climbing directly toward his aircraft and at a distance of 1.3 NM. The CT4 pilot therefore made an immediate broadcast on the CTAF, transmitting his position as 2 NM northeast at 5,800 ft. The Beech 1900 crew responded stating that they were in a right turn passing 5,800 ft. The pilot of the CT4 then observed, through a break in the cloud, the Beech 1900 in his 6 o'clock position at the same level and moving away.

The Beech 1900 crew reported that while maintaining runway heading after takeoff, they levelled at 4,500 ft for a short time to ensure separation. They later stated that they had interpreted the CT4's position as being outbound on the Runway 05 NDB approach and to the south-west of the NDB; therefore, it was not perceived to be a confliction.

The CT4 pilot reported the conditions as generally IMC with a few breaks in the cloud at his level but with no significant vertical visibility. The Beech 1900 continued climbing in a right turn in accordance with the published company procedures for IMC departures at Armidale. The CT4 landed from the runway 05 NDB approach without further incident.

Recorded radio transmissions confirmed that the Beech 1900 crew gave a taxi broadcast for runway 05 that included the phrase "shortly entering and backtracking". They did not subsequently advise that they were about to commence take-off, as directed in the Aeronautical Information Publication. The crew could not explain that oversight.

While cruising at Flight Level (FL) 370 on a flight from Perth to Adelaide, the crew of the Airbus A320 noticed that the left engine bleed-air fault warning had illuminated. The aircraft pressurisation and air conditioning systems then automatically shut down, and the cabin pressure altitude began to increase at approximately 700 ft per minute. The crew made an unsuccessful attempt to reselect the left engine bleed air to on, and the aircraft auxiliary power unit (APU) was started.

The pilot in command (PIC) then contacted air traffic control and requested an emergency descent because of the decreasing cabin pressure, gaining a clearance to descend to 10,000 ft. A short time after commencing the descent the PIC informed the cabin crew and passengers that he was conducting an emergency descent.

As some of the cabin crew were beginning to feel the effects of the increased cabin altitude, all donned portable oxygen breathing equipment. They then took their assigned seating positions in the aircraft. At approximately FL200, the pressurisation and air conditioning systems were restored utilising the APU bleed air supply. The crew then levelled the aircraft at FL180 and told the cabin crew and passengers the reason for the descent. They continued to Adelaide where they completed a normal approach and landing.

The aircraft departed from Perth with a minimum equipment list (MEL) MEL 36-11-07 restriction applied following the failure of the right engine high-pressure valve (HPV). Part of the MEL restriction required that the right engine bleed air HPV be locked in the closed position by a locking pin.

The operation of the engine HPV normally supplemented the bleed air supply to the aircraft at low engine speed. At higher engine speeds, such as occur during normal flight, the bleed-air system was supplied with enough air to operate the air conditioning pack, even with the HPV locked closed.

MEL 36-11-07 was titled "Engine Bleed High Pressure Valve (HPV)" and was composed of two parts. Part (a) detailed the actions to be taken if the bleed-air system was considered to be inoperative and indicated that the bleed-air system was to be isolated and not used. Part (b) detailed the actions to be taken if one HPV was inoperative, "locked closed". However, the intention of the MEL was that the bleed-air system from that engine could still be used except in specified circumstances.

The MEL was part of an operator customised publication, which had been developed from the aircraft manufacturer's master MEL (MMEL). Part (b) of the Operations area of the operator's MEL stated:

"(1) At low engine power (around idle thrust) setting:
(a) Associated bleed is selected OFF.
(b) Cross bleed valve is selected open.
(c) If wing anti-ice is required, one pack is selected OFF".

This differed from the wording of the manufacturer's MMEL, which stated that:

"At low power setting (during descent when thrust setting is in idle position).
Affected ENG BLEED - OFF
X BLEED set - OPEN
If wing anti ice is required
ONE PACK - OFF".

The crew interpreted the operator's MEL to mean that at engine "idle thrust" they were to turn the bleed air from that engine to off. That prevented any supply of bleed air for the pressurisation and air conditioning system coming from that engine. They then opened the bleed air cross-bleed valve and operated both air conditioning packs from the right engine only.

The aircraft then flew with a usable bleed air system isolated. Therefore, when the left engine bleed air system failed, there was a loss of pressurisation and air conditioning. It wasn't until descending below FL200, that pressurisation was able to be restored using the aircraft's APU bleed air source.

A maintenance investigation carried out by the aircraft's operator, found that the left engine bleed-air system was not able to be reselected `on' due to the failure of a temperature control thermostat. The thermostat controlled the temperature of the bleed air from the engine, commanding the position of the fan-air valve. When the signal to control the fan-air valve was lost, the bleed-air system was automatically isolated.

A Cessna 404 Titan aircraft was engaged in low level geophysical survey work near Tennant Creek, NT. The pilot reported that as he was manoeuvring the aircraft at the completion of a survey run, he became aware that the aircraft's response to aileron control input was reduced. He was able to roll the aircraft to wings level attitude using a combination of aileron and rudder, before climbing the aircraft to approximately 6,000 ft and returning to Tennant Creek aerodrome.

Examination of the aileron control system by company maintenance personnel revealed that one of the aileron cables had separated near a change of direction pulley below the control pedestal in the cockpit. Company maintenance personnel reported that there were no obvious signs of fatigue or wear at the failure point and that the reason for the failure was not immediately apparent. The cable could not be identified by manufacturer or part number.

The aircraft had undergone a routine scheduled maintenance inspection 29 hours prior to the event. The engineer reported that it was difficult to inspect the cable in the area beneath the control pedestal during normal scheduled inspections. It was suggested that the only way to adequately examine it would be to disconnect and remove it in accordance with the manufacturers major maintenance requirements.

The aircraft logbooks showed that the aircraft was manufactured in 1981, and had been imported into Australia from Indonesia. At the time of the occurrence, it had a total time in service of 3,853 hours. The aircraft logbooks did not indicate any previous replacement of the aileron cable.

The maintenance engineer advised that, following the incident, he submitted the cable and a detailed major defect report to the local CASA office. CASA Airworthiness advised that their examination was not able to identify the reason for the failure with any certainty. They confirmed that there were no serial or part numbers on the cable and that it was probably not the correct specification for this type of installation. The most likely scenario was that the cable was manufactured and fitted to the aircraft in Indonesia.