Sequence of events

A Boeing 737, VH-CZA, departed Maroochydore for Sydney and was tracking southbound on air route H62. The crew planned to cruise at flight level (FL) 350 but experienced turbulence at that level. Several other aircraft had encountered turbulence at various levels up to FL350 but those at FL370 were in smooth flying conditions. Consequently, the crew had obtained approval from air traffic control to climb to non-standard level FL370 well before the aircraft was handed off to the Inverell sector controller.

A Boeing 737, VH-CZX, departed Melbourne for Brisbane, tracking via air route H29 and on climb to the flight planned level, FL370.

The air routes crossed near the Gibraltar non-directional navigation beacon.

The crew of CZA reported maintaining FL370 to the Inverell sector controller at 1322 Australian Eastern Standard Time.

At 1323, CZX was identified to the Inverell sector controller by the previous sector controller. The crew of CZX made radio contact at 1327, and reported that they were maintaining FL370. Between 1327 and 1329, the controller issued arrival and sequencing information to the crew. This information did not change the aircraft's current route or flight level.

The operational shift supervisor commenced a conversation with the Inverell sector controller at 1330 regarding the selection and testing of radio frequency outlets for that sector. The controller was performing other tasks and said that he would call the supervisor back. Between 1330 and 1332, the controller spoke with the crews of seven aircraft, including asking one of them for a radio check of readability after changing the radio outlet settings.

At 1332:30, the controller contacted the supervisor to discuss the selection of primary and secondary transmitters and receivers. During this exchange, the short-term conflict alert activated at 1333:22 due to confliction between CZA and CZX. The supervisor deselected the intercom line without further conversation.

The controller immediately issued a radar vector to the crew of CZX to effect avoiding action. The crew commenced the turn as instructed and received a traffic alert and collision-avoidance system (TCAS) resolution advisory to climb. They carried out the TCAS climb during the turn.

In the next 15 seconds, the controller passed traffic information on CZX to the crew of CZA. The crew of CZX then informed the controller that they were initiating a TCAS climb, and the crew of CZA broadcast that they were descending in accordance with a TCAS resolution advisory.

Analysis of the radar display data indicated that the radar vector took CZX across the flight path of CZA at 1333:46 while maintaining FL370. At that time, CZA was 10 NM north of CZX and also at FL370.

The point of closest proximity was 3.9 NM at 1334:11, when CZA was descending through FL369 and CZX was maintaining FL370. The required separation for that situation was either 5 NM horizontally or 2,000 ft vertically.

Traffic alert and collision-avoidance system (TCAS)

Each aircraft's TCAS functioned in accordance with design parameters. They activated at about the same time, and assisted the crews to respond appropriately.

The first warning the crew of CZX received was an instruction from the controller to turn right immediately. They commented to each other that the controller sounded worried and commenced the turn without delay. As they started the turn they received a TCAS traffic advisory and then a resolution advisory to climb. The pilot in command remembered seeing a "00" indication, which meant the aircraft were at the same height. The crew did not see the other aircraft, due to the turn manoeuvre, but carried out a climb in accordance with company standard operating procedures. They received a "clear of conflict" message after climbing 400 ft. The aircraft remained within a 500 ft excursion of its cleared level.

The crew of CZA had asked for FL370 due to uncomfortable turbulence at FL350. They had been at FL370 for some time and were unaware of the approaching aircraft until the TCAS activated a traffic information advice at the 12 NM extremity of the TCAS display. The pilot in command only had time to consider that advice before the traffic advisory activated and he looked up to see the other B737 straight ahead and in a turn. He heard the controller issue a right turn instruction to CZX and was confident that he could maintain visual separation behind that aircraft. However, when the resolution advisory activated, he commenced a descent in accordance with company standard operating procedures. The aircraft remained within a 500 ft excursion of its cleared level.

Air route and airspace design

Air routes H62 and H29 were subject to heavy air traffic movements and had to cross at some point. Air route design ensured that they crossed in the middle of the Inverell sector while at cruising levels. That design had the effect of producing a common crossing conflict in the centre of the display screen that provided the controller maximum time to recognise and rectify a conflict.

Inverell sector controller

The controller operating the Inverell sector was experienced in the position and reported that the traffic level at the time was moderate. The controller also reported experiencing significant personal factors that would have been likely to cause him considerable stress in the weeks prior to the incident.

The controller had taken several days off duty in the previous two weeks due to illness. He was current in only two of the four positions for which he held a rating, having registered 9.5 hours on the Inverell sector in the past 22 days and 3.5 hours in the last 15 days. The currency requirement was for at least 2 hours every 14 days for each rating.

The Civil Air Traffic Services Operations Administration Manual (CATSOAM) parts 5.2 and 5.3 outline the recency requirements for maintaining a valid air traffic control licence. In practice it was possible for some of the time logged to fulfil the recency requirements for a particular control position to be worked during times of low traffic levels. For example, working a nightshift where several positions were combined may have allowed a controller to credit the hours worked to more than one position.

In the 14 days before the day of the incident, the controller had worked only one shift; a night shift involving combined sectors for which he held ratings. That shift enabled him to meet the recency requirements to exercise the privileges of his air traffic control licence on two of his four ratings, including the control position he occupied at the time of the incident.

During the controller's absence, the Byron Group of sectors was moved to a different aisle within the Brisbane Centre. Although each sector was a stand-alone unit, the sectors each side of Inverell were then different. The controller reported that the repositioning of the sectors made the "feel" of the surroundings seem unusual when he arrived at the console.

When the controller arrived to start work at 1100, he had no immediate console function to perform and decided to read the documentation relevant to his ratings to catch up on the latest changes. While on that break a personal distraction resulted in him having to leave the console. Consequently, he did not take over the sector until approximately 1310.

A short time later (1324:30), the controller gave an instruction to the crew of a Dash 8 that they did not read back correctly. That was not recognised by the controller and was rectified only after an enquiry by the crew.

The controller received the correct coordination in respect of both CZA and CZX. He realised the potential conflict and checked, on at least two occasions, the relative distance of each aircraft from the intersection of the air routes, but did not subsequently take any positive action to ensure separation; even though the aircraft were 10 minutes from that intersection.

The controller was asked by the supervisor to check the radio system and, although initially saying that he had some other tasks to perform and that he would call the supervisor back, he commenced the radio checks soon after receiving the request and during a period of comparatively busy radio activity. The controller reported that he felt under pressure to complete the task without delay. That pressure was largely self-imposed as the supervisor had left the timing of the task to the controller's discretion. However, the controller was aware that the technicians were waiting at a remote location for the check to be performed and he wanted the task completed.

During that time the controller also changed the transmitter and receiver functions on the voice switching and communication system, thinking he was carrying out the changes requested by the supervisor. However, equipment-fail "bleeps" were evident as he was asking a pilot to comment on the quality of the radio transmission. Those bleeps indicated that the selections made were not correct and the controller's discussion with the supervisor confirmed that he had made an incorrect selection.

The controller stated that although he had acknowledged that CZA was at FL370, he was not fully aware that the aircraft was at a non-standard level. He was concentrating on the voice switching and communication system and the potential problems for sequencing aircraft that were soon to enter his airspace.

The controller stated that had allowed his "scan" to be diverted and, when the short-term conflict alert activated, he knew immediately what the problem was and acted to rectify the infringement of separation standards. He was unable to explain either his poor task prioritisation or his memory lapse.

Short-term conflict alert

The short-term conflict alert was designed to activate when the system checks determined that the aircraft were within 1 minute of coming within 4.1 NM and 600 ft. Analysis of the recording medium indicated that the alarm provided approximately 16 NM warning of the point of closest proximity. As the closing speed was approximately 15 NM/min, indications were that the system activated within reasonable tolerances.

Operational shift supervisor

The supervisor was dealing with radio frequency outlet problems on two sectors. He tasked the other sector first, as Inverell was the busier. Radio technicians at Point Lookout found equipment that needed replacement, but the task required the primary transmitter to be unavailable for about 24 hours. Before authorising its removal, the supervisor needed to check that the standby arrangements for the Inverell sector were satisfactory, and contacted the controller to have them checked. When the controller replied that he was busy, the supervisor waited for his return call. Two minutes later, the controller returned the call. The supervisor said that he thought that it was acceptable to the controller to commence conversation, otherwise he would not have returned his call. During that conversation the supervisor heard an alarm and immediately terminated the call. Although he did not know the nature of the alarm at the time, it was the short-term conflict alert that the supervisor heard.

History of the flight

The pilot of a Cessna 402C aircraft, VH-NMQ, was conducting a scheduled passenger service from Tindal to Darwin, with 4 passengers.

During the climb to the planned cruise altitude of 8,000 ft, the fuel quantity gauges indicated that fuel was being consumed from the left tank only. At the top of climb, the fuel gauges indicated 100 lb in the left tank and 200 lb in the right tank. Once established in the cruise the pilot tried to balance the fuel load by positioning the left fuel selector to allow the left engine to be supplied with fuel from the right tank.

Approaching the midway point between Tindal and Darwin, the fuel gauges confirmed that the imbalance remained. The pilot assessed that sufficient fuel was available to continue to Darwin. As the flight approached the last suitable alternate aerodrome, the pilot calculated that 13 lb of fuel was needed to reach Darwin from that point, based on the current consumption rate. The left fuel tank gauge showed 40-lb remaining.

The pilot requested and was given a direct approach to runway 29. During the landing roll the left engine stopped, and the right engine stopped soon after the aircraft cleared the runway. The fuel quantity gauges showed 20 lb for the left tank and 200 lb for the right tank.

The operator's ground support staff then towed the aircraft to the terminal area where the passengers disembarked normally.

The aircraft had flown from Darwin for Tindal the previous day with 650 lb of fuel on board. The pilot's navigation log showed that 365 lb was required for the flight from Tindal to Darwin. This comprised 230 lb flight fuel (59 minutes), 100 lb fixed reserve (30 minutes), 25 lb variable reserve fuel, and 10 lb taxi fuel. The navigation log also showed the total fuel on-board at Tindal before departure for Darwin was 385 lb. The pilot reported that before departure from Tindal, the aircraft fuel quantity gauges showed 185 lb in the left tank and 200 lb in the right. The pre-flight check of the fuel cross-feed was normal.

A landing at an alternate aerodrome was not considered necessary, as the pilot had calculated sufficient fuel was available to continue to Darwin, and was conscious of the operating schedule for the aircraft. However, company management stated that there was no instruction or pressure on pilots in this regard.

The pilot held a current commercial pilot licence, a command multi-engine instrument rating a valid medical certificate, and had logged 2,454 hours aeronautical experience. This included 150 hours on Cessna 402C aircraft. The pilot's last proficiency check was on 8 March 2000.

On the day of the occurrence, 5 May 2000, the pilot did submit an incident report to the operator. However, due to a breakdown in the operator's reporting procedures following staff changes, the ATSB was not notified of the occurrence until 15 May. As a result, it was unable to conduct an examination of the fuel selector system fitted to NMQ before the aircraft was returned to service.

Background

The then Civil Aviation Authority of Australia issued Civil Aviation Advisory Publication No: 234-1 (0) in March 1991. It provided advice about the quantity of fixed reserve fuel to be carried, and noted the use of fixed reserve fuel was limited to unplanned manoeuvring in the vicinity of the destination aerodrome. It further noted that fixed reserve fuel would normally be retained in the aircraft until the final landing.

The operator's fuel policy stated that in all foreseeable circumstances an aircraft should complete a flight with at least the fixed reserve fuel intact. The standard fixed reserve for the operator's Cessna 402C fleet was 100 lb of fuel for 30 minutes of flight.

Cessna 402C Fuel Selector System

The two fuel selector controls are attached to the cabin floor between the pilot and co-pilot seats. The selectors enable the fuel selector valves, located behind the engine firewalls, to be positioned to the corresponding tank, crossfeed, or off. The arrow-shaped ends of the selector control handle points to the position on the selector placard that corresponds to the control valve position. Each handle connects directly to a gearbox located under the floor. Cables connect each gearbox to their respective fuel selector valve.

An inspection by the maintenance provider in Darwin confirmed that the pilot had positioned the right fuel selector handle to the right tank. However, the cable connecting the gearbox to the fuel selector valve did not position the valve to the right tank.

The right fuel selector gearbox was removed, the selector gearing adjusted and the selector cable re-rigged. The aircraft was returned to service after the fuel selector system was ground tested.

The Pilot's Operating Handbook for the aircraft contained a description of the fuel system and it's operation. In the Normal Procedures section of the handbook, pilots were cautioned that they should "Feel for (the) detent" when placing the fuel selector at the desired position.

Maintenance action

The operator's maintenance controller was located at Alice Springs. A sub-contract maintenance provider conducted maintenance at Darwin. The operator's maintenance controller was not advised of the occurrence until 23 May, and was therefore unable to specify extra inspection procedures for the operator's Cessna 402C fleet until that time. The maintenance controller issued maintenance alert MA/C400/2 on 25 May. It was applicable to all Cessna 402C aircraft used by the operator and its associate company, and required a detailed inspection of the fuel selector system. These checks were to be conducted at each scheduled inspection until the requirements were included in the operator's System of Maintenance.

During one such check of the fuel selector system on another of the company aircraft, VH-TZH, the screws securing the selector cable lever arm/travel stop to the sector gear were found to be loose. This allowed the travel stop to slide under the base-plate and the sector gear to move beyond the end of its travel, resulting in loss of synchronisation between the selector handle and the selector valve.

The operator immediately issued an amendment to maintenance alert MA/C400/2 that included photographs of the defective fuel selector on TZH. The alert specified that the selector gearbox was to be checked if the fuel selector valve was found not synchronised with the selector indicator. During the investigation the fuel selectors of two other of the operator's Cessna 402C aircraft were found to lack an effective detent.

At the time of the occurrence, the maintenance release for NMQ contained an annotation arising from a previous report of uneven fuel consumption from the left tank. Examination of the fuel system related maintenance documentation for the aircraft revealed 17 events since December 1999. Seven involved reports of the aircraft using more fuel from the left tank than the right when the fuel selectors were correctly positioned. There was one report of greater fuel usage from the right tank. The rectification section for four of the entries stated that the fuel selector system was re-rigged. The reported defect for three of the entries was annotated "not major defect" and transferred to the deferred defects list. The fuel related defect entry for the 18 April 2000 stated "fuel not feeding correctly. Fuel noted to be crossfeeding some fuel in level flight - report further".

The last reference to fuel transfer problems, prior to the incident, was on 20 April. The endorsement on the trip record stated "both engines draw fuel from the left tank only". The rectification section of the record noted the fuel selector valve was removed, lubricated, refitted and pressure tested. The selector cable was re-rigged, and the system operated satisfactorily during ground testing.

Fuel system pre-flight checks

The fuel system pre-flight checks specified in the operator's Cessna 402C Operations Manual differed from the procedures specified in the manufacturer's Pilot's Operating Handbook.

The operator's standard operating procedures required pilots to operate the fuel supply cross feed for 60 seconds to verify normal operation. Also, pilots were to ensure normal operation of the fuel valves by positioning the fuel selectors to the off position to observe a decrease in fuel flow. Following these checks, pilots were to position the fuel selectors to the main tanks.

The manufacturer's Pilot's Operating Handbook did not specify checks for crossfeed operation or positioning the fuel selectors to the off position to observe a decrease in fuel flow.

The pilot did not move the fuel selectors to the off position as part of the pre-flight checks. This was because the Fleet Manager had advised his intention to amend the pre-flight check to delete the requirement. The pilot reported awareness of the need to feel for the detent when moving the fuel selectors, and was confident the detent was achieved during the pre-flight check.

On 16 May the operator issued a memo on the occurrence to its Cessna 402 pilots, and included new instructions for pre-flight operation of the fuel selector. The memo cancelled the previous requirement for pilots to position the fuel selectors to the off position to confirm a decrease in fuel flow.

The crew of the Fairchild Metroliner was conducting endorsement training in the Cowra area when they advised air traffic services (ATS) that their aircraft had a hydraulic failure and they were returning to Bankstown. An uncertainty phase was declared by ATS and the aircraft returned to Bankstown where a flapless landing was carried out.

The subsequent maintenance inspection found a cracked hydraulic pipe in the left landing gear wheel-well that had allowed the loss of the hydraulic oil contents from the power pack. The crack was in the bend radius of the pipe and was not visible to the naked eye. The crack only became apparent with the application of more than 800 psi of hydraulic pressure to the system during the maintenance inspection. The pipe was changed and the aircraft returned to service.

The pilot in command reported that he had experienced two similar hydraulic pipe failures in this aircraft type and the company fleet had five or six similar failures in the preceding twelve months. He also reported that he had a concern that the escaping oil in this situation could have started a wheel-well fire.

The design of the hydraulic system is such that, when a failure occurs in one of these hydraulic pipes, there is no redundancy. As a result, the leak drains the contents from the hydraulic reservoir, which is the common source of hydraulic fluid for both the left and right engine-driven hydraulic pumps. Without hydraulic services, nosewheel steering, anti-skid braking, flap operation and normal landing gear retraction and extension would not be available to the pilot.

The Piper PA34 Seneca III, took off from Canberra for Bankstown under the Visual Flight Rules (VFR). The pilot in command had planned to embark five passengers at Bankstown then to conduct a scenic flight around Sydney Harbour, proceed to Cessnock for lunch and return to Bankstown where he intended to disembark the passengers before returning to Canberra.

The flight to Bankstown was uneventful. On departure from Bankstown, the pilot proceeded southeast to the coast and then north, at low level, along the VFR coastal route to Manly. A delay was experienced at Manly, prior to turning south and entering Sydney Harbour. The Sydney Harbour scenic flight was then conducted, completing a circuit of the Harbour Bridge to Rushcutter's Bay loop. The pilot then returned to South Head and proceeded north via Aeropelican for a landing at Cessnock.

During the return flight, the pilot deviated west of the planned track in order to avoid severe weather that had been indicated on the aircraft's weather radar. Shortly after passing Brooklyn Bridge, which was the start point for the northern inbound VFR track to Bankstown, at an altitude of 2,500 ft, the pilot reported that the left engine suddenly stopped. The pilot reported that he then carried out the engine failure checks from memory, feathering the propeller. Approximately one minute later, the right engine began to gradually lose power, before stopping after approximately a further 20 seconds. The pilot reported that he then pushed all of the engine and propeller controls forward and attempted to restart the engines. That action resulted in the inadvertent unfeathering of the left propeller due to operation of the unfeathering accumulator.

The pilot conducted a forced landing into a treed area beside a main road. The aircraft struck the trees, rotated to the right and impacted the ground left wing forward. Four of the six occupants sustained serious injuries and the aircraft was destroyed.

Pilot information

The pilot was appropriately licensed for the flight and had accumulated a total of 270 hours flying experience with 14 hours on the aircraft type.

Flight and fuel planning

The aircraft arrived on the operator's flight line five days before the accident, after delivery from Tamworth. The technical log indicated that the last recorded refuel had been conducted at Tamworth on 13 March 2000. Between that time and the delivery flight to Canberra the aircraft had undergone a 15-minute dual engine run following a propeller change. The engine run included a period of one to one and a half minutes with both engines at full power. Prior to departure from Tamworth, the delivery pilot reported that he visually assessed the fuel tanks as full. Upon arrival at Canberra, the fuel tank content was assessed as 280 L, using flight time and fuel usage calculations.

The pilot planned the accident flight utilising a computer-based flight planning application. He did not plan for any aerial work at Sydney Harbour, despite having an intention to conduct a scenic flight in that location. Air Traffic Services (ATS) radar data indicated that the scenic flight duration was approximately 12 minutes. In addition, he planned the flight using figures for full fuel tanks, however he used the total fuel tank content figure of 465 L instead of the useable fuel tank content figure of 454 L. Further, he was aware that the aircraft had only an assessed 280 L of fuel on board and considered that that amount was sufficient for the flight from Canberra to Cessnock and for the return flight to Bankstown. He had decided not to add fuel prior to departure from Canberra due to a perception that the aircraft would be over Maximum Take-off Weight at Bankstown or Maximum Landing Weight at Cessnock, after the addition of the five passengers.

Fuel management

The pilot reported that he visually checked the fuel tank contents at Canberra before departure, with fuel just visible through the fuel cap opening. That quantity was then cross-checked with the aircraft fuel gauges and it appeared to agree with the previously calculated total. An attempt was also made to check the fuel tank contents using the aircraft's fuel dipstick, however, that was unsuccessful as the fuel level was well below the lowest graduated scale on the stick. The pilot reported that he again checked the fuel level on arrival at Bankstown. At that time the level was out of sight of the fuel caps, however, the total fuel remaining on the fuel gauges appeared to agree with his assessment. Prior to landing at Cessnock the fuel gauges were again checked, with the pilot considering that the indicated fuel level was what he expected from his mental calculations to allow for the return flight to Bankstown.

ATS radar data indicated a total flight time of 159 minutes from take-off at Canberra to the accident site. That figure did not include any allowance for ground taxi at Canberra, Bankstown and Cessnock. Using the operator's recommended fuel usage planning figure of 100 L per hour, 159 minutes flight time would have consumed 265 L of fuel.

The aircraft manufacturer's recommended engine fuel leaning procedure for cruise flight was detailed in Section 4 (Normal Procedures) of the Pilot's Operating Handbook, which stated:

"For 45, 55 and 65% power the mixture should be leaned to 25 [degrees] F rich of peak E.G.T. [Exhaust Gas Temperature] but not to exceed 1,650 [degrees] F E.G.T.", and "For maximum engine service life, cylinder head temperatures should be maintained below 420 [degrees] F..."

The pilot reported that he had been taught to lean the fuel mixture to the top of the green arc on the exhaust gas temperature gauge. The green arc on the gauge extended from 1,200 to 1,525 degrees F. He reported that during the accident flight he leaned the mixture according to that method, however he had subsequently enriched the mixture one or two graduations below the top of the green arc. Advice from the aircraft manufacturer and other Seneca III operators, indicated that that action may have increased the fuel flow by up to approximately 10 L per hour.

Approximately one litre of fuel was recovered from the aircraft wing tanks, however the fuel tanks had been substantially damaged during the impact sequence. There was no evidence of fuel leakage on the ground. Inspection of the fuel system components revealed no evidence of fuel contamination. The left engine fuel selector control was positioned at the OFF position and the right engine selector was positioned at ON.

Engine and fuel system information

Both engines had recently been overhauled and had flown 57.3 hours since fitment to the aircraft.

During the flight, a short time after passing Aeropelican, the pilot reported that the left engine had required increased throttle to maintain the selected manifold pressure. While taxying after landing at Cessnock the left engine appeared to idle slower than before and the alternator light flickered on and off. The light had extinguished when the pilot increased engine RPM. After vacating the aircraft, the pilot noticed evidence of an oil leak along the outboard side of the left engine cowling, on the underside of the left wing and on the left flap. A check of the left engine oil quantity revealed that the engine had used about half a quart during the flight. Confirmation with the operator by telephone indicated that the oil level was within tolerances. The source of the oil leak was not able to be located. The pilot reported that operation of both engines from departure at Cessnock to the point of engine failure appeared normal.

Technical investigation at the accident site revealed that the left engine number 4 cylinder exhaust rocker pivot was loose and that the rocker had contacted and holed the inside surface of the rocker cover. The forward rocker pivot-retaining stud had sheared flush with the surface of the head with evidence of a fatigue failure on the stud fracture surface. The number 4 cylinder inlet valve push rod had also failed close to the outboard tip of the rod. Detailed technical examination of both engines at an engine overhaul facility noted that the exhaust valve on the number 4 cylinder of the left engine remained closed during rotation of the crankshaft and the inlet valve on the same cylinder only opened a small amount. Both engines were then test run in an engine test cell. The test run of the right engine revealed no condition that would have contributed to the in-flight loss of power. The test run of the left engine indicated that it was capable of operation, however it's performance was affected by the damage evident on the number 4 cylinder's valve mechanism.