Sequence of events

The co-owners of the Piper Twin Comanche aircraft, both of whom were pilots, were conducting the flight to test a newly fitted left propeller governor.

At about 1650 EST, one of the owners telephoned the aircraft refueller and requested fuel for VH-CNZ. When the refueller arrived at the aircraft a short time later, he was requested by the other pilot to refuel the aircraft to full tanks. The refueller reported that this pilot appeared to be conducting a preflight check of the aircraft while the other pilot was seated in the cockpit, possibly in the left seat. The refueller noticed that the fuel filler flap covers were open and that the fuel tank filler caps, two on each wing, one on either side of the engine nacelles, had each been removed and placed on the wing adjacent to the filler points. After adding fuel to the right auxiliary fuel tank, the refueller placed the cap in the filler port. The pilot who was doing the external inspection approached him and said that he would secure the caps because they had a locking mechanism that was different from those fitted to many other aircraft types. The refueller then filled the right main tank and placed the cap in the filler port. As he moved away, he saw the pilot move to the tank. The refueller then moved to the left side of the aircraft and filled the left auxiliary and left main tanks, again placing the caps in the filler port of each tank. He did not secure the caps and left the flap covers open. At this stage, he saw the pilot lying beneath the fuselage, apparently conducting a fuel drain check. The refueller recorded in the refuelling register that 179 litres of fuel had been added to the aircraft at 1700. He then told the pilot seated in the aircraft the amount of fuel he had added, and reminded her that he had not secured the fuel caps. The refueller then moved to refuel another aircraft.

A short time later, the aircraft taxied for takeoff. Visual meteorological conditions existed with scattered light cloud at 3500 feet. The wind was from the southeast, gusting to 5 knots. Sunset on the day of the accident was at 1658. At the time of the accident, the sun was 3.5 degrees below the horizon, bearing 292 degrees True.

The following is a summary of the pertinent communications between the aircraft (CNZ) and Archerfield Tower (Tower), which commenced at 1714.14.

• 1714.14 (CNZ) Archer Tower Twin Comanche Charlie November Zulu is ready runway 10 right departing to the southeast (male voice).
• 1714.26 (Tower) Charlie November Zulu Tower runway right cleared for takeoff.
• 1714.31 (CNZ) Runway right cleared for takeoff Charlie November Zulu (male voice)
• 1715.21 (Tower) Charlie November Zulu there is smoke coming from one of your engines (pause) it's the left engine.
• 1715.31 (Tower) Charlie November Zulu did you copy.
• 1715.36 (CNZ) Charlie November Zulu affirm we're shutting it down and request a left turn back for landing (female voice).
• 1715.43 (Tower) Charlie November Zulu left turn approved.
• 1715.45 (CNZ) Charlie November Zulu (female voice).
• 1716.23 (Tower) Charlie November Zulu clear to land.
• 1716.27 (CNZ) Clear to land Charlie November Zulu (female voice).

Several witnesses observed the progress of the aircraft. Their observations confirmed that a cloud of what appeared to be 'greyish black smoke' coming from both sides of the left engine. The aircraft yawed sharply left and right just after becoming airborne and then commenced a left circuit at very low level, estimated to have been 100 ft above ground level. The landing gear remained extended throughout the circuit. Approaching the western boundary of the airport, the aircraft entered another left turn, passing low over some buildings. Part way through the turn, the aircraft's angle of bank suddenly increased and it descended rapidly into the ground. Both occupants were fatally injured.

Wreckage and impact information

Initial examination at the accident site revealed that the fuel filler flap covers of the two left wing tanks were open, and both filler caps were missing. The caps were recovered the following day from runway 10 right and the adjoining clear way. Fuel wetting was evident on the ground below the open fuel caps of the inverted left wing. A total of approximately 35 litres of fuel was recovered from the damaged right wing fuel tanks. The recovered fuel was confirmed as the correct type and grade for the aircraft. The accident aircraft was the thirteenth of sixteen refuelled from the same batch and tanker on the day. The records show that the fuelling agent had sample tested the fuel on three previous occasions throughout the day. Given that there were no reports of fuel related problems from any other aircraft and because of the obvious level of performance from the right engine. The quality of the fuel as a factor in the development of the accident was discounted.

The aircraft wreckage was located in an open area adjacent to the western boundary fence of the aerodrome, approximately 250 metres north-northwest of the threshold of runway 10 left. Impact marks indicated that the aircraft was inverted and rolling left when it struck the ground. The aircraft attitude was 55 - 60 degrees nose down and 25 - 30 degrees left wing low. The main wreckage came to rest about 17 m beyond the initial impact point. The tail section was right way up and the main wing section was folded back on top of the rear fuselage. The cabin area was severely distorted, with the instrument panel and cockpit floor displaced rearward.

Specific points noted during the wreckage examination included the following:

• There was no evidence of either pre-impact or post impact fire including to the left engine. (PA30-160 aircraft, along with most other light twin engine aircraft, were not equipped with fire detection or suppressant systems.)
• The landing gear was locked in the extended position and the wing flaps were fully retracted. Impact damage prevented the serviceability of the stall warning system being assessed.
• The nature and extent of damage to the cockpit engine control pedestal prevented any useful witness mark information being obtained regarding the pre-impact position of the controls.
• Ground contact marks and the condition of the right propeller blades indicated that the right engine was developing significant power at impact. Ground contact marks and the condition of the left propeller blades indicated that the left propeller was rotating at impact but that the engine was not developing power.

The constant speed governor from the left engine was recovered; the only obvious damage being slight bending to the control-input shaft which was consistent with impact damage. The governor was functionally tested at an approved overhaul facility. The tests met all the manufacturer's specifications, with the exception of the maximum RPM setting that indicated 2285. This was 45 RPM below the specification. Specialist opinion was that this discrepancy could be attributed to the damage to the control-input shaft.

Disassembly of the left and right propellers found no evidence of any pre-existing fault or defect. Disassembly of the left propeller confirmed the blades were at fine pitch and not in the feathered position at impact. Disassembly of both engines did not reveal any pre-existing fault or defect that would have affected normal engine operation.

Fuel tank filler points

The two fuel tank filler points on each wing were located on either side of the engine nacelles. The filler points consisted of filler port, a cap to seal the port, and a flap covering the cap access. The cap consisted of a black rubber insert that compressed to seal the fuel filler tank port by the action of a screw grip on top of the cap. The flap cover was secured with a winged slotted 'dzus' type fastener and, when locked, was flush with the upper surface of the wing. Locking the flap cover required deliberate action, and could not be achieved by slamming the cover down. The flap covers were hinged parallel to the longitudinal axis of the aircraft, and opened away from the engine nacelles. The slotted 'dzus' fasteners had to be locked for the flap covers to be closed flush with the wing surface. If not locked, the flap covers would stand slightly proud of the wing surface.

The left and right wing filler points, inboard of the engine nacelles, were visible from the left and right cockpit seats, respectively. They may have been visible in the pilot's peripheral vision, depending on the pilot's seating position. With the flap covers open, there was a high level of contrast between the white painted upper surface of the wing and the dark underside of the flap covers and filler cavity. In reduced light conditions, the level of contrast would have been lower.

When in the open position, the outboard flap covers were partly visible from the cockpit. If those covers were down, but not locked, they were not visible from the cockpit.

The 'dzus' fastener locking mechanism for the flap covers on the left wing tanks functioned normally. Aside from damage caused to one cap when it was struck by an aerodrome mower operating on the runway 10R flight strip on the morning following the accident, both fuel caps from the left wing tanks were in a serviceable condition.

The pilots

Both pilots were appropriately licensed and held current medical certificates.

Toxicological and Post-mortem analysis did not reveal the presence of any compound or pre-existing medical condition that may have affected the performance of either pilot.

Aerodrome information

Runway 10 Right was 1100 m long. Beyond the runway end was a flat area extending for more than 400 m, and free of major obstacles, to the aerodrome boundary fence. The distance from a position on the runway abeam the control tower to the boundary fence was about 800 m.

The control tower cab was 65 ft above ground level. The controller reported that when the aircraft passed abeam the tower, its level appeared to be slightly below that of the tower cab. With respect to the control tower, the remaining light or glow from the sun was behind and slightly left of the position of the aircraft, as it became airborne.

Aircraft performance

The aircraft flight manual performance charts indicated that, in the prevailing conditions, the take-off ground run distance required was about 350 m, depending on the flap setting used. The observations of the tower controller indicated that the actual take-off performance of the aircraft was not substantially different from that figure.

The landing distance over a 50-ft obstacle was approximately 500 m, depending on the aircraft flap setting and approach speed.

Single engine performance

The sea level single engine climb performance of light twin engine aeroplanes certified in accordance with United States Federal Aviation Regulation 23 requirements can be up to 70 to 90 percent less than the twin engine performance. Many factors can contribute to this performance loss such as aircraft age and condition, leaving the landing gear extended, not feathering a propeller, not maintaining the correct airspeed, and not turning towards the live engine.

The Pilot's Operating Manual for the aircraft included information on propeller feathering procedures and single engine flight. That information included the statement that, when climbing with one engine inoperative, the landing gear and wing flaps must be retracted.