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.

While in cruise flight between Bundaberg and Brisbane, the crew of the Shorts 360 aircraft heard a loud noise followed by the automatic feathering of the right propeller. The crew shut down the right engine, declared a PAN and continued to Brisbane.

Initial investigation by the operator found that the engine would not rotate. Subsequent specialist examination revealed that the number 1 bearing had failed. The surfaces of the bearing showed signs of discolouration and blackening associated with extreme overheating. The bearing balls and inner race showed heavy localised wear and metal flow associated with the sliding contact of the balls against the inner race. There was also evidence of electrical arcing damage on the inner race. That was traced back through the accessory gearbox components to the starter-generator input shaft. Four equally spaced groups of two or three teeth on the starter-generator drive gear were pitted. The electric current required to cause that pitting was an alternating or pulsed frequency, equal to four times the rotational speed of the starter gear. The coupling gear that mated with the starter-generator drive gear showed continuous pitting over the whole contact surface.

Tests carried out by the operator on a starter-generator of the same model as that fitted to the failed engine, showed pulsed electric current discharges from the starter-generator output shaft. When an accumulation of armature brush dust was blown from the housing of the starter-generator, the measured voltage of the pulsed discharge decreased. The investigation noted that during overhaul, the starter-generators may be fitted with Federal Aviation Administration (FAA) Parts Manufacturer Approval (PMA) components, such as rotor electrical brushes.

The operator had previously experienced four engine failures in Shorts 360 aircraft. Those occurred in November 1995, June 1999, October 1999 and April 2000. All involved failure of the number 1 bearing. In three cases, there was evidence to suggest that an electric current from the starter-generator gear shaft, passed through the accessory gearbox gear train and the compressor hub splined coupling. The electric current initiated spalling damage to the bearing (the cracking and flaking of particles out of a surface). The reason for the electric discharge was not determined. In one case, the reason could not be determined because of the severity of secondary damage to the bearing. The four inflight engine failures in Australia, attributed to electrical discharge damage to the number 1 bearing, occurred between 60 and 640 hours after the starter-generator became unserviceable and a replacement unit was fitted. There are indications that in some occurrences a previously installed starter-generator may have initiated damage to the number 1 bearing.

The engine manufacturer has since reported that seventeen engine failures attributed to electrical discharge damage of the number 1 bearing have occurred in the PT6A worldwide fleet. The aircraft types involved included the Shorts 360, Beech 1900 and Beech Kingair 350 aircraft. To date, the engine and starter-generator combination has been limited to the PT6A-60A, 65B, 65R, 67D, 67R series engines equipped with Lucas Aerospace (TRW Aeronautical Systems) 23078 and 23085 model starter-generators.

A diagram showing the general construction of the PT6A engine and the relationship between the starter-generator and the number 1 bearing is included in this report available on the ATSB web site at Technical Analysis Report 200003399.

The ATSB Technical Analysis Report 200003399 (BE/200000014) details the examination of the failed number 1 bearing and is also available on the ATSB web site at  Technical Analysis Report 200003399 or from the Bureau on request.

History of flight

Following an earlier flight from the mainland and a brief shutdown on a floating pontoon at Norman Reef, the Bell Jetranger II 206B departed in a south-south-east direction into the prevailing wind. On board with the pilot were four passengers scheduled for a scenic flight around Norman Reef and return to the pontoon. Immediately following the takeoff, the pilot initiated a right banking turn. While in the turn, with a quartering tailwind, the helicopter began an uncommanded yaw to the right. The pilot reported that he lowered the collective and pushed the tail rotor pedals left and right in an attempt to regain control of the helicopter. Following those actions, and after two complete 360-degree rotations to the right, the yaw abated. After a momentary pause, the helicopter again began to yaw to the right. The pilot broadcast a MAYDAY on CTAF frequency, armed and inflated the emergency flotation gear, and initiated a water landing. The helicopter impacted the water and rolled to the right. The pilot and three occupants successfully exited the helicopter unassisted. One passenger occupying the right rear passenger seat was momentarily trapped in the helicopter by her seatbelt, as the seatbelt release latch had become reversed. The pilot and onlookers from a nearby pontoon eventually assisted her from the helicopter. The helicopter sustained substantial damage.

Weather

The forecast for the area was for isolated showers along the seacoast with winds from the south-east at 15 knots, with broken Stratus 1000 to 2000 feet in showers. Observations of the weather at the nearby pontoon recorded at 0700 hours Eastern Standard Time indicated wind from the south-southeast at 15 knots with no cloud and a temperature of approximately 22 degrees Celsius.

Wreckage examination

All flotation bags of the emergency flotation gear activated upon selection. The helicopter had impacted the water with approximately 10 degrees nose-down attitude, little forward airspeed, and a slight right-bank. The advancing main rotor blade contacted the water causing separation of the main rotor hub and displacement of the main transmission. The retreating blade impacted and severed the tail boom, tail rotor controls, and the tail rotor driveshaft. The transmission-to-engine driveshaft, transmission upper deck, and forward engine firewall were also damaged following transmission displacement. The damage was indicative of at least partial drive train continuity at the time of impact. No pre-existing mechanical defect was discovered that would have resulted in loss of tail rotor control. It was determined that the helicopter was capable of normal operation prior to the accident.

Helicopter information

The Bell 206B II Jetranger helicopter was manufactured in 1973 and was first entered on the Australian Civil Register on 17 April 1973. The part number 206-016-201-133 tail rotor blades had been installed in March 1999. Those blades were longer length than the standard blades, with improved performance, and therefore believed to be less susceptible to loss of tail rotor effectiveness (LTE). The helicopter was last reweighed on 4 October 1996. The empty weight of the helicopter, according to the last weight and balance calculations of 20 May 2000, was 897.6 kilograms. The maximum allowable gross weight of the helicopter was 1,451 kilograms. The estimated takeoff weight using the May 2000 calculations was 1,357 kilograms. The helicopter's flight manual was not recovered to permit confirmation of the flight manual weight and balance documentation.

Personnel information

The pilot had a total of 1,281.3 hours on rotary wing aircraft, including 751.8 hours on type. He had recorded 114.4 hours on this particular helicopter. The pilot held a valid Commercial Pilot's License (Helicopter), Bell 206 type endorsement, and Class One medical certificate. The endorsement was issued on 15 November 1997. The pilot's last flight review was completed on 20 August 1999. He had completed a 0.3 hour basic introduction check ride with the company chief pilot on 11 April 2000. Thereafter, he accompanied other company pilots operating in the local area, until he was permitted to fly as pilot in command.

The pilot had been on duty for six hours leading up to the accident and had 15 hours off duty before the work period, including 8.5 hours sleep the night prior to the accident. He had flown this particular helicopter 5.2 hours the day before the accident, with a total duty time that day of 8.5 hours. He had a rostered day off two days prior to the day of accident.

Loss of Tail Rotor Effectiveness

The phenomena of LTE, also known as unanticipated right yaw, has been identified as a contributing factor in several helicopter accidents. According to United States Army testing, OH-58 series helicopters (the Bell 206 series is the civilian variant) have proven in the past to be susceptible to LTE under certain low speed manoeuvres. LTE is not related to a maintenance malfunction and is associated with single main rotor, tail rotor configured helicopters. LTE is a result of the tail rotor losing aerodynamic efficiency due to a combination of several factors. Those factors include main rotor vortex interference and tail rotor vortex ring state (related to airflow disruption over the tail rotor), helicopter weathercock stability, and the loss of translational lift. The regimes in which LTE may be encountered include low airspeed (less than 30 knots) when translational lift is lost or reduced, high power, and in the case of the United States designed helicopters, operating in a left crosswind or tailwind or with a high yaw rate to the right.

There is greater susceptibility for LTE on United States designed helicopters in right turns and more so in right turns overwater. This is especially true during flight at low airspeeds when the pilot is looking out the right window (not viewing the instrument panel) and is unaware of the airspeed dropping to a low value. The turn is commonly done with reference to the ground where the pilot attempts to keep a constant groundspeed by referencing ground cues. Flying overwater, the pilot does not have the visual cues available as when flying overland.

In turbine powered helicopters, the frame of reference for the engine power governor is the main rotor RPM (Nr) with reference to the airframe. Once the helicopter begins spinning rapidly to the right as during the onset of LTE, the governor will sense a false increase in Nr and reduce fuel flow to the engine in order to maintain what it believes to be a constant Nr with reference to the airframe. Any reduction in Nr will result in a corresponding reduction in tail rotor RPM, with an associated reduction in the effectiveness of the tail rotor.

Recommended LTE recovery techniques

Correct and timely response to the uncommanded right yaw associated with LTE by immediately applying full left pedal and decreasing power and main rotor blade pitch requirements, will usually counter the condition. However, if the pilot's response is incorrect or slow, the yaw rate may rapidly increase to a point where recovery is not possible. The pilot expressed no knowledge of recommended recovery techniques to counteract the onset of LTE.

In response to several reports of unanticipated right yaw incidents, the Federal Aviation Administration circular AC 90-95 recommends the following recovery techniques:

a. If a sudden unanticipated right yaw occurs, the pilot should perform the following:
(1) Apply full left pedal. Simultaneously, move cyclic forward to increase speed. If altitude permits, reduce power.
(2) As recovery is effected, adjust controls for normal forward flight.
b. Collective pitch reduction will aid in arresting the yaw rate but may cause an increase in the rate of descent. Any large, rapid increase in collective to prevent ground or obstacle contact may further increase the yaw rate and decrease rotor rpm.
c. The amount of collective reduction should be based on the height above obstructions or surface, gross weight of the aircraft, and the existing atmospheric conditions.
d. If the rotation cannot be stopped and ground contact is imminent, an autorotation may be the best course of action. The pilot should maintain full left pedal until rotation stops, then adjust to maintain heading.

Furthermore, Bell Operational Safety Notice (OSN) 206-83-10 states that "An unanticipated right yaw may occur under certain conditions not related to a mechanical malfunction. These conditions may include high power demand situations while hovering, and/or when relative wind affects airspeed versus ground speed." The OSN recommends recovery techniques as follows:

1. Apply full left pedal.

2. Apply forward cyclic.

3. If altitude permits, reduce power.

Organisational Factors

The company did not have systems in place to address the organisational aspects that were identified as factors contributing to the accident. These were:

1. The company had no formal pilot induction program. Newly inducted pilots were not required to perform flight checks in areas reflective of actual operating conditions.
2. The Chief Pilot did not document and maintain individual files on each line pilot. Line pilots were not required to perform flight checks in areas reflective of actual operating conditions.
3. Flight checks were not regularly scheduled and were of short duration.
4. The company had no Flight Safety Program in place.
5. The company had no formal system of maintenance control and no assigned maintenance controller. Non-compliance with maintenance requirements and unapproved maintenance was reported on company helicopters.

These were not required by regulation.

CASA surveillance

This operator was also involved in a fatal accident in March 1999. CASA Flying Operations Surveillance Guidelines-Variations to Normal Surveillance includes significant safety related incidents as typical triggers justifying long-term increases in scheduled surveillance. No special audit of the organisation was completed following the fatal accident. A Flight Operations Inspection completed on 29 January 1999 identified several discrepancies. The inspector's report included a note recommending increased surveillance of the organisation. CASA regional management also requested authorisation from the CASA central office for increased surveillance of the organisation, however, the surveillance level of the organisation remained the same.

An Airworthiness Inspection (ramp check) was completed on 12 April 2000. During that inspection, three discrepancies were noted against the helicopter. Included among these was one noting "flight manuals contain expired weight control documents". Prior to the accident, there was no documentation on the CASA files to indicate acquittal of the discrepancy.

Following this accident, a CASA team completed a special audit of the organisation during 11-17 August 2000. The special audit resulted in the CASA team issuing a safety alert to ensure all required maintenance was completed on company helicopters and six requests for corrective action to resolve safety concerns. The company corrected these discrepancies and continued charter operations following the audit.

CASA surveillance documentation

CASA utilised the ASR (Aircraft Survey Report) Aviation Safety Surveillance Program (ASSP) 604 form to outline discrepancies noted during airworthiness inspections of aircraft and helicopters. According to the CASA ASSP manual, inspectors and team leaders were responsible for the monitoring of acquittals of ASRs. The forms did not require the Certificate of Registration holder to carry out rectification action within any particular timeframe.

CASA utilised a form called the Safety Trend Indicator to analyse significant factors related to the operator's risk level. That form included a question concerning the non-acquittal of Non-compliance Notice (NCN) ASSP 603 forms within the last 12 months. No response was required concerning non-acquittal of ASR ASSP 604 forms.

When the pilot began the right banked turn, he exposed the helicopter to firstly, a left crosswind, then a quartering tail wind. Flying at low airspeeds and operating out of ground effect, the helicopter was satisfying several of the operational conditions necessary to experience an uncommanded right yaw or LTE as outlined in Bell OSN 206-83-10.

The pilot indicated no awareness of operational conditions necessary to experience LTE, or knowledge of recovery techniques to counteract the onset of LTE. The failure of the helicopter to recover from the LTE condition following the pilot's reported corrective actions, was probably a result of his lateness to recognise the onset of LTE in sufficient time to permit recovery.

Organisational Factors

CASA's audit of August 2000 found that the checking of line pilots by the Chief Pilot was irregular and ineffective. Pilot flight checks were conducted in areas unreflective of actual operating conditions. In addition, those flight checks were of insufficient duration to appropriately assess the pilot's skills. Safety awareness training of personnel was considered inadequate. The operator had not established a sufficient maintenance control program. This resulted in the operation of company helicopters with overdue maintenance requirements. The lack of a formal pilot induction program, adequate checking of line pilots for currency, adequate documentation of line pilot training, a company Flight Safety Program, and a formal system of maintenance control all contributed to a less than adequate safety culture within the company.

CASA surveillance

The March 1999 fatal accident may have justified an increase in surveillance as per CASA guidelines. CASA management however, did not revise surveillance of the operator following recommendations from area managers and Flying Operations Inspectors. As a result, the safety oversight of the operator by CASA may have been less than recommended in CASA guidelines. Following this latest occurrence, CASA subsequently increased its level of surveillance of the operator.

CASA surveillance documentation

Examination of the CASA aircraft file for this helicopter and other aircraft files, has identified a trend of non-compliance by operators to resolve discrepancies noted on the ASR ASSP 604 form. Non-acquittal of ASRs could also display a trend of non-compliance to airworthiness issues.

1. The pilot did not have adequate knowledge in recognition of operational conditions that could have induced LTE.

2. The pilot did not correctly identify operational conditions that could have induced LTE.

3. The pilot did not implement adequate recovery techniques to counteract the onset of LTE.

As a result of this investigation the Australian Transport Safety Bureau has identified a safety deficiency related to pilot training. The results of the investigation of this safety deficiency will be published on the Australian Transport Safety Bureau website.

As a result of this investigation on 9 March 2001, the Australian Transport Safety Bureau issued the following recommendations to the Civil Aviation Safety Authority.

R20010015

The Australian Transport Safety Bureau recommends the Civil Aviation Safety Authority consider revising Civil Aviation Safety Authority Safety Aircraft Survey Report 604 form to require a response date for acquittal of discrepancies.

CASA response to recommendation R20010015 dated 10 April 2001.

The ASR (Aircraft Survey Report) can be assigned either Code A, B or C.

Code A identifies a defect or damage to the aircraft, and requires that maintenance to rectify the defect or damage must be carried out before further flight. This acquittal requirement is very specific in relation to the aircraft operational requirements. However, if the Certificate of Registration (CoR) holder removes the aircraft from service, an actual acquittal date has no relevance. The requirement to perform the maintenance before further flight remains.

Code B is a direction under CAR 38(1) to have defects or damaged assessed and rectified as necessary. The Code B direction is used to bring a defect or damage to the attention of the CoR holder, the pilot or operator where:

- A defect or damage to the attention of the CoR holder, the pilot or operator where:

- The inspector considers the defect or damage to be minor, or; The inspection carried out on the aircraft does not enable proper determination if the defect or damage is major. In which case the C of R holder, the pilot or operator is responsible to have an assessment carried out to determine the true nature of the defect or damage, and have appropriate rectification carried out. While the assessment needs to be done prior to further flight, the rectification might not be accomplished for some time in the future, where, for instance, the defect is minor and falls within the provision of Permissible Unserviceabilities.

Code C is used to give the C of R holder formal notification of a non-compliance with a requirement or condition imposed under the regulations and is judged, on the basis of the inspection, not to have an immediate adverse effect on safety. However, the matter is required to be assessed and rectified at the earliest opportunity.

As can be seen from the above discussion, it is often the case that an acquittal date cannot practically be imposed at the time of issue of the ASR. However, CASA is currently reviewing the ASR process to see how that process might be more closely monitored.

ATSB actions concerning CASA response to R20010015

The ATSB classifies this recommendation OPEN- MONITOR, pending CASA review of the ASR process.

As a result of this investigation on 9 March 2001, the Australian Transport Safety Bureau issued the following recommendations to the Civil Aviation Safety Authority.

R20010016

The Australian Transport Safety Bureau recommends the Civil Aviation Safety Authority consider revising Civil Aviation Safety Authority Safety Trend Indicator form to indicate organisational non-acquittal of Aircraft Survey Report ASSP 604 forms within the last 12 months.

CASA Response to Recommendation R20010016 dated 10 April 2001.

Non-acquittal of an ASR within a particular time period does not necessary reflect poorly on an operator. Consequently, for ASR acquittal information to be meaningful, in regards to Safety Trending, would need complex and prescriptive criteria to be developed and followed by CASA inspectors in the field.

Depending on the outcome of the review mentioned in Para 2 above, CASA would also explore what useful application that information might have in regard to the Safety Trend Indicator.

ATSB actions concerning CASA response to R20010016

The ATSB classifies this recommendation OPEN- MONITOR, pending CASA review of the ASR process.