Collision with terrain

The pilot reported that while on approach to a three foot hover, he commenced a right turn to position the aircraft for refuelling. As he did so an unsecured object in the cockpit shifted, preventing movement of the cyclic control to the left. The pilot tried to recover the situation by increasing altitude, but the aircraft continued to roll right until the main rotor blades hit the ground. The aircraft was then thrown back onto its skids after which it rolled onto its left side.

The pilot reported that when the aircraft was about 300ft on final approach to runway 14, he noticed that the right engine rpm did not change as the propeller controls were set to fine pitch. The aircraft then yawed to the right when it became necessary to introduce power to avoid undershooting the runway.

Both propellers were selected to feather when the yawing moment became uncontrollable, at about 50ft AGL. The right wing struck the ground, the landing gear collapsed, and the right wing was torn off during the ground slide as the aircraft slide off the runway onto the grass flight strip. The two occupants were not injured and evacuated the aircraft unassisted.

Post flight inspection by a licenced aircraft maintenance engineer found that both propellers were on the coarse pitch stops and had not feathered.

Inspection of the suspect right engine failed to find a fault which could have contributed to a power loss.

The pilot was under the impression that he had feather both propellers when he experienced directional control difficulties. Examination of both propeller hubs found that the propeller blades were on the coarse pitch stops. The propeller pitch control levers require a distinct movement to pass the coarse pitch stops into the feather position. It is apparent that the pilot did not position the levers where he intended.

The pilot lost control of the aircraft on late final approach. The reason for the loss of control could not be determined from the evidence available.

The strip direction at Riddell is 15/33. The intention was to fly circuits. There was a northerly wind blowing so take-off was on the 330 degree strip. A storm was approaching from the south and during the circuit the pilot listened to the Essendon ATIS which indicated that the wind was going around to the south.

On final approach the pilot noted that the windsock was indicating that the wind had swung around the southwest and was about 12 to 15 knots. He had flown a fairly tight circuit. Carburettor heat was selected on base when power was reduced and deselected on final approach. The pilot estimated that carburettor heat was probably only on for about 10 seconds.

Approach to the 330 degree strip is over a gully. On short final the aircraft encountered some wind shear and began to sink below the glide path. The pilot pushed the throttle forward but there was no response from the engine. Further sink was encountered, and it became obvious that the aircraft was going to touch down before the airfield boundary fence. The aircraft touched down heavily, ran into the fence and slowly went over onto its back.

Post accident inspection of the engine did not reveal any mechanical reason for the lack of response to throttle application. Information from the Bureau of Meteorology showed that conditions were conducive to the formation of serious carburettor icing at any power setting. The pilot thought that because carby heat was only applied for about 10 seconds, carburettor ice was the only reasonable explanation for the loss of power.

A witness reported that, after turning base for runway 12, the aircraft began oscillating in pitch as it continued a shallow descent. The aircraft crossed the extended centreline of the runway and struck a tree at the edge of a public car park. This caused the aircraft to break up, part of it falling on an unoccupied vehicle.

The pilot is reported to have indicated that the aircraft stalled and that he was unable to recover to normal flight before colliding with the tree.

The pilot had completed two thirds of the task of spraying a field of cotton which was bounded by a road and powerlines at one end. The pilot had been flying under the wires and had kept a watch for traffic along the road. On what turned out to be his last pass, he again lined up to fly under the wires. As he approached the wires, he saw a truck travelling along the road, on a collision course with his aircraft. Trees had obstructed the truck from view. As the pilot took avoiding action, the right mainwheel of the aircraft struck the road surface. The right main gear was bent backwards. The pilot flew his damaged aircraft to the airstrip and landed. At a slow speed it ground looped and came to rest without any further damage.

The flight was an attempt by the pilot to achieve the 500km Goal Flight. During the flight the pilot was unable to find continuing lift and an outlanding became necessary. During the landing the right wing struck grass at the boundary of a paddock and the glider ground looped.

The pilot had misjudged the approach and overshot his intended touchdown point. He had also forgotten to lower the landing gear.

The chief flying instructor was conducting initial multi engine endorsement training for a commercial pilot.  It was the student's fourth session.  After practising simulated engine failures at about 3000 ft in the training area, the aircraft was flown to Tyabb for circuit training.

On the third circuit, on base for landing to the south on the 1000 metre airstrip, the instructor failed the right engine by placing the mixture lever into the idle cut-off position. He told the student not to feather the right propeller but to continue with a touch-and-go landing, thereby experiencing an approach and landing with a failed engine and an unfeathered propeller.  The student selected two stages of flap and, on final, placed both propeller pitch levers into the full fine position.  She closed both throttles before touchdown.  During the landing roll the instructor raised the flaps and advanced the right mixture lever to the full rich position.  Then the student advanced both throttles fully, expecting take-off power on both engines.  At this point the indicated airspeed was about 70 knots. The minimum control speed for single engine operations is 69 knots.  The left engine produced take-off power but the right engine failed to deliver power.

Initially, when the aircraft began to yaw to the right, the instructor thought the student was having difficulty with directional control which she had experienced on previous landings. However, when the aircraft yawed further right, he identified a failed right engine and quickly took over the controls.  By then a collision with runway lights, gable markers and a shallow drainage ditch was imminent, despite the application of full left rudder by the instructor.  He chose to maintain full power on the left engine and become airborne, hoping to avoid the obstacles immediately ahead and find a clearer area to land. The aircraft flew for about 290 metres at a low height in a southerly direction within the airfield boundary but outside the runway gable markers with the instructor struggling to maintain control.  Then the right wing collided with a two metre high pile of old stumps.

The outboard section of the right wing, including the outboard fuel tank, was torn off.  The aircraft turned right through about 260 degrees while remaining upright. It then settled onto the ground and slid backwards, coming to rest about 30 metres beyond the stumps.  As the aircraft came to rest it caught fire.  The right-wing spar was completely broken, and the right engine was torn out of the airframe.  The pilot and the student escaped through flames.  Fire quickly gutted the cabin.

In the seconds between taking over the controls and impact with the stumps, the pilot did not attempt to feather the propeller of the failed engine because of the difficulty he encountered controlling the aircraft at low airspeed. If the RPM of the windmilling propeller had decreased below 800, which it probably had, then feathering would have been prevented by the design of the propeller mechanism.

The airframe was subsequently examined by engineers who found no fault which may have contributed to the accident.  No fault was found with the left engine which had produced take-off power on demand. No fault was found with the right engine.  Aviation gasoline was found in the fuel lines and in the fuel tanks.  There was adequate fuel on board for the flight. The cockpit switches were destroyed by fire.

From the time the instructor selected the mixture to idle cutoff until the student attempted to achieve take-off power during the attempted touch-and-go landing was probably less than two minutes.  The reason the fuel injected engine did not restart when the mixture lever was advanced was not determined.   Witnesses reported hearing a "backfire", probably from the right engine, at about the time full power was selected.

Initially when the right engine failed to deliver power, there was sufficient remaining runway ahead for the pilot(s) to have closed the throttles and stopped the aircraft safely before the end of the runway.  The student, who considered closing the left throttle, did not dare to do so once the instructor took over.  Having taken over the controls, the instructor was confronted with obstacles immediately ahead, which he cleared by becoming airborne. He was then confronted by another obstacle, the pile of stumps which he was unable to avoid.

Four or five times in this aircraft, recently, the instructor had successfully performed a touch-and-go landing after shutting down an engine with the mixture lever during multi-engine endorsement training; once per candidate towards the completion of their endorsement.  On all previous occasions the shutdown engine produced full power when the mixture lever was advanced, and the throttle opened fully.  The instructor's hope was that the training exercise would be a valuable experience for the students.  However, in hindsight he realised that the exercise enhanced the chances of an accident occurring if the shutdown engine did not restart quickly during the touch-and-go.

Since this accident it has become apparent that many multi engine flying instructors, approved testing officers and flying operations inspectors have varying opinions as to whether engines should be shut down completely in the circuit or at low level, as opposed to selecting zero thrust settings appropriate to the particular aircraft.

CONCLUSIONS

Findings

1. The instructor and student were properly licenced and qualified for the task.
2. The aircraft was serviceable and after the accident no faults were found that may have contributed to the accident.
3. The right engine did not deliver power when the mixture and throttle levers were advanced for the touch and go landing. The reason why the right engine did not restart was not determined.
4. The flying instructor underestimated the risk involved versus the training advantage of shutting down one engine at low level followed by a touch-and-go landing.

Significant factors

The following factors were considered relevant to the development of the accident:

1. The instructor shut the right engine down during approach.
2. The instructor briefed the student to fly the approach and land with the engine shut down and the propeller windmilling.
3. During the subsequent touch and go landing, the engine did not restart/deliver power when the mixture and throttle levers were advanced.
4. When the aircraft then began yawing to the right the instructor initially believed the student was having ongoing difficulty with directional control.
5. When the instructor identified that the yaw was due to asymmetric power and took control of the aircraft, the situation with aircraft performance, runway remaining and surrounding terrain was such that an accident was inevitable.

SAFETY ACTION

The following safety action is being taken:

1. The Civil Aviation Safety Authority (CASA) will release a Civil Aviation Advisory Publication containing an initial multi engine endorsement training syllabus.
2. The Bureau of Air Safety Investigation will conduct a research project on advanced training accidents.
3. Since this accident, CASA has held industry symposiums to discuss standardisation of multi engine training procedures.

The aircraft was making an approach to a gravel surfaced strip in CAVOK, light wind conditions with no turbulence. The pilot reported that full flaps were extended, and a final approach speed of 75 knots was maintained until touchdown, which was slightly short of the strip threshold.

The right main wheel struck soft ground, dislodging the right main landing gear. As the aircraft continued onto the strip the remaining landing gears were also dislodged, resulting in major damage to the aircraft. All four occupants were able to exit the aircraft safely.

The pilot had initially planned to land to the north on a strip which was about 950 metres long. When he saw that a formation flight was preparing for a take-off to the west on the 400-metre strip, he decided land to the west. The wind was a light north westerly. He reported that his aircraft touched down near the 270 threshold at 60 knots with full flaps and then bounced a couple of times before he attempted a go-around. The local chief flying instructor (CFI) witnessed the accident from one of the formation aircraft and said that the aircraft looked to be faster on touchdown, more like 65 knots.

During the attempted go-around, the pilot selected flaps fully up and full power but almost ran out of strip before becoming airborne. While attempting to avoid a tree near the end of the strip, he stalled the aircraft which then settled onto a fence.

The CFI believed that the go-around would have been successful if the pilot had selected the flaps up in stages rather than going from full flap to zero flap while attempting to become airborne in a short distance.

The pilot reported that the flight departed from an agricultural strip located in a valley surrounded by hills. The aircraft carried a full load of superphosphate to be spread on a property approximately one mile from the strip. The pilot had previously surveyed the property and the flight path. He had selected a route that took him up through a valley between hills and then over a low ridge to the property.

After take-off the pilot set climb power and selected climb flap in order to follow his predetermined route to the property. The pilot advised that as the aircraft flew towards the low ridge it appeared to be descending rather than climbing. He elected to carry out a partial dump and to apply extra flap to clear a clump of trees. The speed deteriorated to 60 knots from the initial climb speed of 70 knots. The pilot did not increase power.

Some 300 metres later another partial dump was carried out to clear another tree. As that tree was cleared the pilot again initiated a partial dump and turned to the right in an endeavour to escape from a rapidly deteriorating situation. Immediately the turn was initiated the right wing dropped and the aircraft stalled, impacting the ground onto the right wing and cartwheeled to a stop some 50 metres from the initial impact.

The company chief pilot examined the accident site and advised that the flight path through the valley was in a classic false horizon situation whereby the surrounding hills caused the pilot to consider that the flight path was over flat terrain whilst in reality the terrain was rising approximately 5 degrees up to the ridge. The chief pilot also advised that the aircraft would not have been able to outclimb the terrain at high gross weight with only cruise power set.

Examination of the wreckage did not disclose any pre-impact factors that may have contributed to the accident. Weather and pilot workload were not considered to be factors in this accident.

The pilot had flown approximately 1200 hours on agricultural operations and 244 hours on the type. His loss of situational awareness could be due in part to his relatively low experience.

Significant factors

The following factors were considered relevant to the development of the accident.

(1) At high weight, and with climb power applied, the pilot flew the aircraft on an inappropriate flight path into rising terrain.

(2) The pilot did not take appropriate remedial actions when the aircraft could not outclimb the terrain and the aircraft speed deteriorated.

(3) The pilot lost control of the aircraft while attempting a turn at low speed.