Collision with terrain

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 take-off. 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 take-off.
• 1714.31 (CNZ) Runway right cleared for take-off 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.

The student pilot of a Grob 115 C aircraft was authorised by his instructor to conduct solo night circuits at Merredin, WA. Shortly after take-off from runway 28, and as the student commenced his after take-off checks (at about 300 ft AGL, including flap retraction and engine power reduction), he noticed that the aircraft was becoming difficult to control. As he scanned the aircraft's flight instruments he decided that the attitude indicator was unreliable and noted the directional indicator turning quickly to the left. Control inputs applied to reduce the rate of turn were unsuccessful. The student recalled that the airspeed indicator was indicating 140 kts.

The student reported that despite applying back-pressure to the control column and maintaining the pitch attitude for a climb, the aircraft continued to descend and impacted the ground beyond the aerodrome boundary. Immediately following the ground impact, the aircraft became airborne and the student recalled applying full power and commencing a climb. An instructor on the ground established radio communication and provided instructions to assist the student. The student stated that the attitude indicator remained unreliable for the entire circuit but, with the instructor's assistance, he was able to complete a normal approach and landing. As the nose was lowered to the runway during the landing roll, the propeller struck the runway and stopped. The accident occurred at approximately 2000 Western Standard Time. The student was not injured and vacated the aircraft without assistance.

Examination of the aircraft indicated that the nose wheel and oleo had been damaged during the initial impact with the ground and had detached from the aircraft prior to landing. The nose oleo was subsequently recovered from a paddock in the vicinity of a left base position for runway 28.

Last light at Merredin on the night of the accident was 1802. It was reported to be a dark night, with no discernible natural horizon. During the initial climb from runway 28, the student had no significant external visual reference available and was using the flight instruments to maintain control of the aircraft.

Following the accident, the operator contracted an independent maintenance organisation to examine the aircraft flight instruments, engine driven vacuum pump, and other associated systems. No pre-accident defect was detected.

The flying roster for the day indicated that the student was scheduled to complete two separate exercises, a navigation phase check during the afternoon, followed by solo night circuits. The student had arrived at the aerodrome at 1000 to prepare for his phase check.

A delay in departure time for the phase check meant the aircraft arrived back at Merredin after last light. Prior to concluding the phase check, the instructor completed three circuits with the student for the purpose of authorising his solo night flying. The total flight time for the phase check was recorded as 3.3 hours, of which 0.2 hours was logged at night. By 1845, all tasks associated with the phase check were completed and the student took a short meal break before recommencing duty for the night circuits.

The operator had a detailed flying training syllabus for the conduct of training. It was reported that a gap in the flying program had permitted some students to progress through their training at an accelerated rate, which introduced night flying at an earlier stage of training than was usual. The student had been previously assessed proficient in the required syllabus items for solo night circuit operations and had attained this standard in less than the minimum flight time contained in the operator's flying training syllabus.

At the time of the accident, the student's flying training included 3.6 hours dual night instruction, 2.5 hours night pilot-in-command, 4.4 hours instrument flying and 2.7 hours in a synthetic trainer. The syllabus indicated that a student required at least 9 hours in a synthetic trainer prior to commencing his night training, including a requirement for 5 hours of night simulation in the synthetic trainer. There was no provision for an exemption against those operations manual requirements.

Sequence of events

The pilot of a Pitts aerobatic aircraft arranged to fly to a training area to the south of Archerfield in company with a friend in a Yak aerobatic aircraft. They planned to practise aerobatics for about 30 minutes. The area selected was over a pine forest with a duplicated high-tension power line traversing the forest. North of the power lines the trees had been cleared and grass to about 500 mm high was the only significant vegetation in the area. The terrain was gently sloping up towards the north-west. The pilots agreed to operate on either side of the power line with the Pitts operating to the north of the line.

When the pilot of the Yak aircraft completed his sequence he attempted, unsuccessfully, to contact the Pitts pilot by radio. He also could not see the aircraft. When he flew closer to the power line he observed a small fire and realised that the Pitts aircraft had crashed. The pilot then contacted the Archerfield Air Traffic Controller to alert emergency services.

A resident located north-east of the accident site had observed the Pitts aircraft flying manoeuvres parallel to the power line. During one manoeuvre conducted to the north-west and away from the observer, the aircraft appeared to be flying straight, with the wings vertical, as if in a manoeuvre known as a "knife-edge". The upper side of the fuselage was directed away from the power line. The aircraft appeared to be descending but the person was aware that the aircraft was moving away and thought that the apparent descent may have been an illusion. After a vertical climb and descent involving rolling manoeuvres, the aircraft again flew in a straight line with the wings vertical. On that occasion the aircraft was tracking to the south-east and toward the observer, and the upper fuselage was again oriented away from the power line. The observer stated that the aircraft appeared to be descending, and passed from sight behind a low ridge. He did not see the aircraft again and sometime later saw smoke rising from behind the ridge.

Aircraft examination

The aircraft impacted the ground in a wings-level attitude at a speed estimated at more than 100 kts, while travelling in a north-westerly direction. At the time the aircraft was descending at about 30 deg nose down, and appeared to have been in balanced flight and at a low "g" loading. The impact was considered not survivable. The aircraft did not bounce, coming to an extremely rapid stop in the sandy soil. The fire would have broken out immediately, as a result of the ruptured fuel tank and disruption of the electrical system. The aircraft was destroyed by impact forces and the post-impact fire.

The engine was dissassembled and inspected. The crankshaft had moved rearward by about 6 mm relative to the crankcase, a further indication of an abrupt stop. The lack of damage to the cylinders indicated that the propeller and crankshaft had taken most of the deceleration loads, transmitting them through the crankcase to the airframe. There was no indication of mechanical failure prior to impact. The available information suggested that the engine was operating at low to moderate power at impact.

The Pilot

The pilot held a private pilot's licence to fly aeroplanes. His Class Two medical certificate was valid until June 2001. He had commenced flying training in January 1983 and obtained an aerobatic rating in March 1995. The rating was progressively upgraded, and in November 2000 the pilot was approved to conduct aerobatics to a minimum height of 100 ft.

The pilot purchased the Pitts aircraft in September 1997 and had flown it almost exclusively since then. His most recent biennial flight review, which included aerobatic flying, was conducted in May 1999.

Although he normally flew without a parachute, on the accident flight the pilot was wearing a new parachute pack for the first time. The pack thickness was about 4 cm.

Weather conditions

At the time of the accident the sky was clear of cloud, and the wind was a light south-westerly. The pilot of the Yak aircraft assessed that the temperature was in the mid-thirties [Celsius]. The temperature and humidity at the accident site were considered by an experienced pilot to be such that conditions in the cockpit of the Pitts aircraft would have been oppressive.

Aerobatic manoeuvres

One of the manoeuvres the pilot was intending to practise was a "knife-edge" manoeuvre where the aircraft was flown straight and level while banked 90 degrees left or right. That manoeuvre was referred to as a stick-position manoeuvre, because the positioning of the control column and rudder pedals must be precise to place the aircraft in the correct attitude and flight path. Practice and familiarity are the primary means of ensuring accuracy.

In the immediate vicinity of the crash site there were no prominent visual indicators for the pilot to judge the height of the aircraft above the ground. The vegetation was low and devoid of trees, and the terrain was not sufficiently sloping to provide the pilot with good height cues.

Examination of terrain contours and the location of the observer indicated that the aircraft was probably below 30 ft above ground level at the time it was lost from sight behind a ridge.

The owner/builder of the the Vans RV-6A aircraft was conducting a flight from Townsville to Toowoomba. The aircraft departed Townsville at 0846 local time. The pilot subsequently contacted Oakey Approach at 1324, and the aircraft was identified on radar at 3500 feet. The pilot was instructed to maintain that altitude. When the aircraft was about 26 nautical miles from Toowoomba, the pilot transmitted a mayday distress message stating that the aircraft's engine had failed. A short time later he reported that a propeller blade had failed. No further transmissions were heard from the aircraft. About 30 minutes later, a searching helicopter located the wreckage in a flat clear area amongst hilly, tree covered terrain.

The area apparently chosen by the pilot for an emergency landing was about 300 m long and relatively flat. There were trees under the likely approach path of the aircraft and rising ground at the far end. The surrounding hills were above the level of the landing area.

Examination at the accident site revealed that the aircraft struck the ground while banked about 90 degrees left, and descending at an angle of about 34 degrees. A 200 mm section of one propeller blade tip had broken off and could not be located at the accident site. Witness marks indicated that the propeller was rotating under power when the blades contacted the ground. Aside from the broken tip, the propeller blades were in good condition. No other faults were found that might have prevented the aircraft from operating normally.

During the impact sequence, the section of the fuselage forward of the pilot's seat was deflected upward relative to the rear fuselage. The cockpit sides had buckled outwards. That resulted in the pilot striking the instrument panel, even though his shoulder harness remained fastened.

Aircraft information

The pilot purchased the aircraft in 1996 and he first flew it in 1998. At the time of the accident, the aircraft had accumulated 383 hours time in service.

The pilot fitted a new engine and propeller to the aircraft during construction. The engine was modified to improve and balance the airflow through the valves of each cylinder to enhance engine performance. In an apparent further attempt to improve engine performance, the pilot replaced one magneto with an electronic ignition system that was capable of varying the ignition timing in response to changes in engine RPM and manifold pressure. That variation contrasted with the fixed timing ignition provided by the other "standard" magneto fitted to the engine.

The aircraft's wing was a constant chord, low aspect ratio wing. A characteristic of low aspect ratio wings is high induced drag at low speed. Unless the pilot controls the speed carefully, the effect on aircraft performance can be a rapid speed loss and a high rate of descent. If such a situation arose during an approach to land, the only means of regaining speed and arresting the rate of descent would be to increase engine power. If little or no engine power was available, the outcome could range from a heavy landing to a loss of control of the aircraft.

Examination of the failed propeller blade

A fatigue crack had initiated near the leading edge of the blade 216 mm from the blade tip. Crack growth had occurred as a result of alternating thrust loads, and had propagated along the thrust face (rear surface) of the blade. The characteristics of the crack indicated that it had grown under constant amplitude loading. There was no evidence of flight by flight striations. The propeller material was of the correct type and no damage or other reason for the crack to initiate was found.

All propellers are subject to alternating thrust loads during normal operation. Propellers are designed so that those loads will not exceed the design value, thus preventing the development of fatigue cracks during operation. The firing of each cylinder in a reciprocating engine produces torsional vibrations. That means that the crankshaft momentarily speeds up at each firing stroke, and then slows down again prior to the next firing stroke. The vibration leads to alternating thrust loads in the propeller.

Examination of the engine connecting rod big-end bearings revealed distress on the bearing surfaces. That distress was indicative of firing loads exceeding the designed capacity of the bearing lubrication. For optimum operation of spark ignition engines, the peak pressure developed by the combustion of the fuel air mixture should occur approximately 15 degrees after the crank has located past top centre.

Ignition timing was a critical factor, influencing engine power, fuel economy, and the operating condition of the engine. Timing depended on the rate of propagation of the flame front through the fuel-air mixture. Increased or advanced ignition timing resulted in increased combustion chamber pressures. Magneto timing was fixed and was optimised for the operating range of the engine. If the response of the electronic ignition system to reductions in manifold pressure created by part throttle opening was to advance the timing of ignition, that could increase cylinder head pressures and increase the magnitude of torsional vibration.

Pilot information

The pilot, aged 64, held a New Zealand Private Pilot Licence and a current Class 2 Medical Certificate. The medical certificate was subject to three restrictions; the pilot was required to wear spectacles, he was granted an exemption regarding his hearing standard, and he was subject to a restriction regarding a drug he was taking for tinnitus (a ringing or similar sensation in the ears, due to disease of the auditory nerve).

The post-mortem examination of the pilot revealed that he had previously suffered at least one myocardial infarction and had coronary artery disease. Specialist examination of the pilot's electrocardiogram traces over a number of years did not reveal any pre-existing signs of a heart problem. Specialist medical opinion was that the possibility of the pilot suffering a heart attack induced by high stress levels after the propeller failed could not be excluded.

According to the pilot's logbook, he had a total flying experience of 1,179.6 hours at the time of the accident, of which 1,109.9 hours were in command. He had 383.2 hours on the accident aircraft, all of which were in command. On the day before the accident, the pilot had flown the aircraft from Auckland, New Zealand to Townsville, Queensland. That flight took 13 hours.