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.
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 Takeoff Weight at Bankstown or Maximum Landing Weight at Cessnock, after the addition of the five passengers.
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 takeoff 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.
The aircraft had been assessed as having 280 L of fuel on board prior to departure from Canberra, based upon the delivery pilot's calculation. ATSB calculations, using the operator's own fuel planning figures, indicated that the amount of fuel consumed during the 1.8 hour delivery flight from Tamworth would likely have equated to a fuel remaining figure of approximately 265 L. In addition, no allowance was able to be determined for the amount of fuel consumed during the engine ground runs at Tamworth, between the time of the last recorded refuel and the delivery flight. Accordingly, the actual fuel tank contents on departure from Tamworth for the delivery flight could not be accurately determined and would probably have been an amount less than the maximum useable.
While planning for the accident flight utilising a computer-based application, the pilot used an incorrect figure (465 L) with respect to total versus useable fuel tank contents (454 L). That led the pilot to include 11 L of fuel, which was unavailable for engine consumption. In addition, he omitted to plan an allowance for fuel consumption during the approximately 12 minute Sydney Harbour scenic flight. Using the operator's fuel consumption planning figure, this may have involved consumption of up to 20 L of additional fuel.
The pilot's use of the computer-based flight planning application included calculations for aircraft weight and balance. His utilisation of the full fuel planning figure in these calculations, instead of the assessed fuel load figure of 280 L, may have led to an erroneous perception that he would be overweight following embarkation of the five passengers at Bankstown, if he added fuel prior to takeoff from either Bankstown or Canberra. Had the pilot used the assessed fuel tank content figure, he would have realised that he could have added fuel and remained within aircraft weight limitations.
The manufacturer's fuel usage figures are determined using a recommended technique for leaning of the fuel mixture supplied to the engines. During the accident flight, the pilot deviated from the recommended technique. That deviation would likely have increased the engine fuel consumption.
Technical investigation of the right engine indicated that it was capable of normal operation. Examination of the left engine indicated that it should still have supplied at least partial power in flight. The failure mode of the exhaust valve rocker stud and the bending of the inlet valve pushrod were examined in consultation with a representative of the engine manufacturer and engine overhaul specialists. Although an exact reason for the failure could not be determined, it is possible that the damage may have occurred following the loosening of one or both of the rocker pivot retaining nuts. As the nut(s) loosened during engine operation, the exhaust valve rocker would have lifted, preventing the exhaust valve from opening. During the valve overlap stage of the engine operating cycle, prior to the start of the induction stroke, the ignited and expanding combustion gasses may have been unable to escape through a now closed exhaust valve. That scenario would have greatly increased internal cylinder pressure which could have prevented the inlet valve opening and, consequently, resulted in the bending of the inlet valve push rod as it tried to move the valve. The damage to the inlet valve pushrod was also considered to have been consistent with the rotation of the engine with a "hydraulic lock" situation existing in the cylinder. Such a condition may occur in the cylinder if the engine was overprimed prior to an engine start.
It is likely that the engine failures occurred as a result of fuel exhaustion.
- The pilot's fuel planning was based on incorrect fuel content and weight considerations.
- The pilot did not include the Sydney Harbour scenic flight in his flight planning.
- The pilot diverted from the recommended in-flight fuel management practices.
|Date:||25 April 2000||Investigation status:||Completed|
|Time:||1555 hours EST|
|Location:||13 km S Brooklyn Bridge, (VTC Check Point)|
|State:||New South Wales||Occurrence type:||Fuel exhaustion|
|Release date:||10 April 2002||Occurrence category:||Accident|
|Report status:||Final||Highest injury level:||Serious|
|Aircraft manufacturer||Piper Aircraft Corp|
|Type of operation||Private|
|Damage to aircraft||Destroyed|
|Departure point||Cessnock, NSW|
|Departure time||1526 hours EST|
|Role||Class of licence||Hours on type||Hours total|