Collision with terrain

The helicopter was being used for a controlled firebombing and burning off operation. The pilot had been flying very slowly just above the treetops, then after turning onto a southerly heading he believed the engine lost power and was unable to prevent it from striking the tops of the trees. It then descended steeply into the ground, the pilot receiving severe back injuries, and the passenger a broken arm.

An investigation of the helicopter and engine failed to find any fault, or malfunction, that may have caused the engine to lose power.

Weather conditions were very hot with a light northerly wind blowing.

The helicopters weight was calculated to be in excess of its maximum all up weight, with heavy items of equipment stored in the areas below the seats, contrary to the flight manual and placarded instructions.

Being overweight for the operation, and turning downwind, i.e. to the south, the helicopter probably suffered a loss of translational lift with subsequent overpitching of the rotor system by the pilot, giving the impression that the engine had lost power. With no available height margin the pilot was unable to avoid flying into the trees.

The pilot reported that the aircraft accelerated normally during the take-off run and began a normal climb over tree covered rising ground. At about 100 feet above the tree tops a strong down draught was encountered, which the aircraft was unable to out climb. When it became evident that a collision was inevitable the pilot attempted to stall the aircraft into the trees. The aircraft collided with the treetops and nosed over, coming to rest inverted. Both occupants were able to vacate the aircraft with minor injuries.

The pilot of the accident aircraft released from an aerotow about 4 km south-west of the airfield at 1,800 ft above ground level and immediately encountered strong sink so decided to return for a landing.

At about 2km short of the airfield he realised that the glider would not reach the runway and turned towards a suitable open field for an outlanding. Strong sink was encountered throughout the approach causing the glider to undershoot and strike small fruit trees in an orchard at the edge of the field.

The day had been fine but very hot, with other pilots also reporting areas of strong lift and equivalent sink.

The helicopter on a ferry flight late in the afternoon failed to arrive at its destination. A search found the injured pilot and damaged helicopter the next morning only 4km from the departure point. The pilot had activated the ELT, but it failed to transmit.

The pilot stated that a vibration had developed shortly after departure, and he slowed the helicopter to nearly a hover at about 150 ft above ground level to determine its origin. He planned to land once clear of trees but as he manipulated the anti-torque pedals the helicopter went out of control and crashed heavily on its right side. Due to head injuries suffered during the accident the pilot had difficulty in remembering any details of the accident subsequent to slowing down.

Inspection revealed that marks on a tail rotor blade indicated that it had impacted something while rotating. The tail rotor drive shaft pin, connecting it to the universal joint, had sheared allowing the shaft to spin in the universal joint.

It was not possible to determine whether the connection between the universal joint and the drive shaft failed because of the tail rotor strike, or whether the tail rotor blade was damaged after the connection had failed.

Engineering evidence tends to indicate that something was struck by the tail rotor blades while they were under power. The item may have been similar to an item of clothing or cloth large enough to fail the tail rotor drive path by overload but not hard enough to dent the tail rotor blades. Nothing that fits this description was found in the immediate vicinity of the crash site.

During a winch launch the pilot noted that the glider was accelerating slowly. He considered abandoning the launch but because there was 6000 feet of runway he decided to persist until the winch driver realised that more power/speed was required. The speed slowly increased to 50 knots at which point the pilot made a gentle rotation. As soon as the glider started to rotate the speed fell off dramatically.

The pilot said that he lowered the nose immediately and then saw the ground approaching at a steep angle. He managed to get the aircraft to a level attitude but was unable to prevent it touching down very heavily resulting in substantial damage.

FACTUAL INFORMATION

History of the flight

The flight was planned as a dual instructional flight followed by solo circuits to refamiliarise the student with the C172 aircraft and circuit procedures.

The student pilot had completed several circuits with the instructor during which some improvements to the student’s technique were made. The instructor then alighted, and the student proceeded to conduct further solo circuits.  The instructor reported that he observed two circuits and detected only minor problems in their conduct.  On the planned last circuit of the sequence, the aircraft descended and impacted the ground, some 150 m short of the runway 23 threshold.

The pilot of an aircraft taxiing at Dubbo reported seeing the C172 on what appeared to be a normal final approach followed by a rapid descent to impact the ground, nose first, from a height of approximately 50 ft.  He also reported that the aircraft did not appear to stall.  There was no fire.

The aircraft came to rest inverted.  The fuselage had broken at the baggage door frame and was folded back along the upturned forward fuselage.  The engine and propeller had separated from the airframe and were located in the general direction of the runway, approximately 12m from the main wreckage. The nose landing gear had also separated from the airframe and was located approximately 6m from the main wreckage.  The wing flaps were fully extended and the aircraft contained sufficient fuel for the intended flight.

Personnel information

The pilot held a valid student pilot licence endorsed for C172 aircraft.  He had gained approximately 45 hours in ultralight aircraft prior to his general aviation training.  He had completed approximately 16 hours in the aircraft type and had accumulated approximately 1.5 hours solo experience.  The last time he had flown, which was in the accident aircraft, was 31 days prior to the accident.

The pilot reported that he was well rested prior to the flight.

Aircraft information

The pilot reported that the aircraft had been performing normally.  The investigation found no evidence to indicate a malfunction of the aircraft or its systems.  A post-accident "strip inspection" of the engine revealed no defects which may have contributed to the occurrence.  The aircraft was fitted with a serviceable Emergency Locator Transmitter (ELT), however no emissions were reported by other aircraft in the area. The ELT switch was found in the OFF position at the accident site.

Communications

The aircraft transmissions were recorded by a voice recorder used in revenue collection administration.  These recordings were replayed with the following observations:

• The pilot used standard phraseology throughout the circuit sequence and was consistent in his transmissions.  The pilot used the term "touch and go" on approach to the runway, including the full stop landing to allow the instructor to disembark.  Similarly, although the final approach was intended to be the last for the day, the pilot called "touch and go".
• There was no other recorded traffic during the circuit sequence.  During the last circuit, however, there was another aircraft conducting an approach and an aircraft taxiing at Dubbo, both of which were communicating on the Mandatory Traffic Advisory Frequency (MTAF).  The pilot was wearing a headset to monitor the radio but was using a handheld microphone for transmitting.

Weather

The weather at the time of the accident was reported as fine and clear with a light wind from the south and a temperature of 19 degrees Celsius.  Weather is not considered as being a factor in the accident.

ANALYSIS

This was the pilots first flight after a break of 31 days.   His previous flights had been conducted over a two-day period, which included his first solo flight on the first day.

The initial circuits were conducted with an instructor and some corrections were suggested to the pilot. Similarly, the two observed solo landings had only minor problems which the instructor noted.  The circuit during which the accident occurred was planned to be the last of the session.  On this circuit there was other traffic communicating on the Dubbo MTAF.  This resulted in the pilot having to operate the handheld microphone as well as handle the aircraft and it is possible that, even though he reported being well rested, the pilot was experiencing fatigue toward the end of a reasonably demanding session.  The accumulation of these factors, coupled with the pilot’s low aeronautical experience, may have contributed to the pilot being distracted during the final approach and losing control of the aircraft at an altitude too low to effect a recovery.

CONCLUSIONS

Significant Factor

The pilot lost control of the aircraft at an altitude too low to effect a recovery.

The pilot was spraying a paddock that he had sprayed three weeks previously. As some light rain was approaching, the pilot restricted his flight check of the paddock to one quick circuit. He did not notice the set of wires outside the spray paddock and did not remember them from the previous application.

The pilot completed the first spray run and pulled up to set himself for the second pass. Whilst pulling up, he looked back to check the spray coming from the hopper. The aircraft was approximately halfway through its pull up when contact was made with the wires.

The aircraft crashed a short distance from the wires.

The flight was a night navigation exercise associated with the pilot-under-instruction's (PUI) training for the award of a Night Visual Meteorological Conditions rating. The pilots had completed a briefing before departure, but its content was restricted to flight planning aspects only.

An enroute landing had not been planned, but the instructor decided that the PUI should carry out a touch and go landing at Narrogin when he saw that the north/south runway flare path was illuminated.

The flight was the PUI's third night flying training flight and was his first away from Jandakot at night. Aircraft attitude and directional control at night is enhanced, in the Jandakot area, by the high level of ground lighting which provides a natural horizon. In areas where ground lighting is not available the pilot must rely on the information provided by the aircraft's instruments and in particular the artificial horizon. During the take-off from Narrogin the PUI used an incorrect attitude and directional maintenance technique when he initially selected a wings level, and 10 degrees nose up attitude on the artificial horizon but then attempted to maintain that attitude by holding an indicated airspeed of 75 knots without further reference to the artificial horizon. This resulted in the aircraft entering a left hand descending turn.

The instructor allowed his attention to be drawn away from his pilot monitoring role by an apparently subtle engine r.p.m. fluctuation shortly after the touch and go landing and did not detect the pilot's incorrect technique until too late. When the instructor did perceive that the aircraft was near the ground and took control, there was insufficient time to recover before the aircraft collided with a tree. The aircraft continued to fly without any obvious damage or control problems, and the instructor elected to continue to Jandakot, expecting to have landing gear problems on arrival. These did not eventuate, and the aircraft landed safely at Jandakot.

The student was performing a dual practice forced landing on to an airfield. Strong winds and gusty conditions prevailed. It was the instructor's intention to allow the student to continue the practice forced landing to a low height for realism. The student forgot to lower the landing gear, and the instructor missed the oversight. On short final the aircraft encountered windshear. The instructor was late in nominating the go-around. The aircraft struck the ground wheels up.

It was reported that fuel usage during the flight appeared to be excessive, and the burner flames were more yellow coloured than normal. The pilot suspected a problem with the fuel gas and decided to land before his supply ran out. During the approach, the pilot had difficulty in controlling the descent accurately because of an unusually slow response to control burns. Following three landing attempts, the balloon was landed in pine trees. Eleven envelope panels were torn.

Investigation with the gas supplier revealed that the fuel mixture was not the 97% Propane requested but a mixture of 35% propane and 65% propylene. It was not the first flight using this fuel mixture, but it was the first time that the outside air temperature was as low as +5 degrees Celsius. Subsequent tests by the operator showed that the burners were inefficient with this gas at the lower temperatures.