Collision with terrain

The helicopter departed Mount Green in a northerly direction at approximately 1755 CST, for a survey of the locations of Army personnel in the area who were manning Rapier missile sites. The pilot said that while approaching one of the sites, he descended to approximately 100 ft AGL, and commenced a left-hand orbit while his passenger, an Army officer, was explaining the layout. When he was about halfway through the turn and maintaining approximately 60 knots with about 30 degrees angle of bank, the nose suddenly yawed to the left, and the helicopter descended rapidly in a nose low attitude. The helicopter impacted the ground, and slid backwards into a thicket of small trees 2 to 3 metres high.

One main rotor blade had sustained a spar fracture approximately 14 cms from the blade tip. Blade weight segments were installed in this region and could not be found after the accident. A section of the blade skin and honeycomb core extending over a distance of approximately 34 cms from the blade tip had also been lost. The nature of damage displayed by the blade was consistent with an impact between the blade leading edge and a solid rocky object, at a point approximately 20-25 cms from the blade tip, while the blade was rotating.

A series of unusual paint transfer markings along the upper surface of the leading edge of one main rotor blade was noted during examination. The paint was dark green in colour. Abrasive scores through some of these markings indicated that paint transfer associated with contact with some other material or component occurred prior to collision with the ground. It was established that the blade had struck a ground-to-air missile casing which was painted dark green. The stage in the accident sequence at which this occurred could not be determined.

The pilot reported that the strip had received heavy rain during the previous week and that only 680 m of the 1,000 m length was usable for operations. The centre of the strip was dry, but the edges were soft with water standing in the table drains at the side. The pilot said that the take-off run was normal until lift off when the aircraft lost 15 kts of airspeed as the right main wheel ran through a soft patch.

As result, the climb out was slow and shallow, and the aircraft veered to the right of the strip. The pilot was unable to avoid trees about 100 m to the right of the strip. The left wing struck foliage, but the pilot was able to keep the aircraft airborne. After landing the aircraft to assess the damage, the pilot found that the leading edge of the left wing was damaged.

The pilot of the C188 aircraft was carrying out spraying operations 12 km West of Clare. Due to his low experience level on the C188, the pilot was operating with a reduced internal chemical load of 600 litres rather than the maximum 757 litres. The pilot advised that on entry to a procedure turn at the completion of the fourth spray run he encountered excessive sink due to a tailwind.

The pilot attempted to arrest the sink rate by dumping the remaining chemical load and applying full power, however, due to late manoeuvering to avoid power lines this proved unsuccessful, and the aircraft impacted the ground left wing low. The pilot vacated the aircraft having suffered minor injuries in the accident.

During the approach to land, just prior to crossing the runway end, the right main gear struck an earth mound. The gear leg was damaged by the impact. The mound, about three metres short of the 800-metre runway, was about 25 cm high and not easily seen from the approach path. The wind was light and there were no gusts or turbulence.

The aircraft was carrying out dusting operations and was on the second flight of the day. The pilot had done an obstacle evaluation flight prior to commencement of operations and had identified a row of mallee trees running north/south inside the eastern boundary fence. Running parallel to these trees in the paddock to be sprayed was a single power line.

The pilot made his first run to the west flying through a gateway and then under the power line as there was sufficient clearance and it provided the optimal approach for this swath run. The reciprocal run was then commenced to the east and the pilot began his pull up with a view to clear both the power line and the trees. During this manoeuvre the pilot heard a light thud and believed that he had contacted the power line. As the aircraft appeared to be handling normally, the pilot elected to return to the airstrip to inspect for damage.

Approximately 450 metres past the paddock fence, the aircraft suddenly pulled to the right in a steep nose down attitude and impacted the ground sustaining substantial damage. After evacuating the aircraft, the pilot observed that the power line was still attached to the aircraft landing gear and had not broken. He stated that the local Electricity Trust representative later informed him that the power line was of a three-strand high tensile steel construction that was designed specifically not to be cut or broken. This was evidenced by the ineffectiveness of the aircraft cable cutting devices and the severe damage that they sustained without severing the power line.

The pilot was moving the helicopter in an attempt to prevent cattle from crossing a water channel. During an attempt to reduce airspeed quickly he flared with a 15 kt tailwind, resulting in the main rotor overpitching. The helicopter was levelled but one skid entered water adjacent to the edge of the stream, and the other skid landed on the bank. The skid in the water sank into the sandy bottom and the helicopter slowly rolled on to its side. Considerable damage was caused to the rotor blades and airframe when the blades contacted the water.

An emergency locator transmitter was carried but did not activate during the impact sequence.

The pilot in command and aircraft owner was restricted to flying with a co-pilot because of his age (79). The pilots were carrying out practice for a spot-landing competition to take place later that day.

The pilot reported that his first approach was lower than normal, and he had to apply power in an attempt to reach the runway threshold. Although the wind was blowing directly down the runway, at about 5 kt, there was some turbulence, and he believed there was a downdraft on late, final approach.

The pilot was concentrating his attention on touching down on the threshold markers, as practice for landing on his selected spot, when the co-pilot called "up, up". Immediately after the call, the aircraft collided with the top rail of a cattle holding yard, crashed to the ground, slid across a road and through the airfield boundary fence and onto the runway, where it came to a stop.

The major factor in the accident was that the pilot was concentrating all his attention on achieving his selected touchdown point (tunnel vision) and was not situationally aware in that he was not observing the other required parameters, height above the ground, glide-path angle and obstacle clearance, as he allowed the aircraft to descend well below a safe glidepath. It is possible that a downdraft may have increases the rate of descent in the last seconds of flight.

The pilot reported that he was flying an AT502 Air tractor aircraft in calm weather conditions, applying liquid fertiliser to a cereal crop. Whilst conducting a procedure turn for the clean-up run, he felt one wing drop slightly followed by the other wing. After the third wing drop, he managed to maintain wings level, but the aircraft seemed to be in turbulence and continued to descend. The aircraft struck the ground with the right wing and broke up with the pilot sustaining leg injuries.

The pilot reported that the turn was conducted close to the stall, and he considered that the turbulence experienced was created by the aircraft during the turn.

FACTUAL INFORMATION

Background

The pilot/owner of VH-CSW had been approached some time before the accident with a request to allow passengers to abseil from his helicopter while it was in a hover. The pilot approached a Civil Aviation Safety Authority (CASA) representative who advised the pilot that he would need to submit a proposed amendment to the company's Operations Manual detailing how such flights would be conducted. The representative also advised that any proposed amendment would have to be approved by CASA before any such flights could be conducted and that the representative had already approached a CASA helicopter specialist to discuss safety aspects of the proposed flights.

Because of the CASA requirement for a detailed proposal for conduct of the proposed flights, the pilot decided to conduct some controllability tests prior to submitting his proposed Operations Manual amendment. Because the pilot declined to be interviewed or to supply the investigation with a statement, it is not known whether he conducted any calculations into the lateral centre of gravity (cg) implications of the proposed flights.

The pilot positioned the helicopter to a helipad near the accident site on the morning of the accident and carried out some local flights prior to the accident flight. Another helicopter pilot, who had flown for the company on a casual basis in the past, drove to the area with addition fuel for the day's planned flights.

A briefing was conducted by the pilot to explain how he proposed to conduct the experimental flight. Present at that briefing were the passenger, who had accompanied the pilot to the site in the helicopter that morning and who had an interest in the proposed abseiling flights, the casual helicopter pilot and another local person. A fourth person was also present at the scene but did not attend the briefing.

The proposed flight discussed at this briefing required that an abseiling rope be attached to the outside of the front cross-tube of the skid assembly of the helicopter and that one passenger be seated in the right seat of the helicopter. The rope would be attached in such a manner that it hung over the outside edge of the right skid tube. The pilot then intended to lift the helicopter to a hover about 10 m above the helipad and the casual pilot was briefed to walk under the hovering helicopter and to gradually apply his weight onto the abseiling rope. One of the persons briefed earlier had radio communication with the pilot through a hand-held radio transceiver.

History of the flight

The flight proceeded as planned initially and the pilot was able to remain in control of the helicopter with one person, the other pilot, who weighed about 70 kg, suspended by the abseiling rope. The person at the helipad stated that the pilot then contacted him by radio and asked that the other person standing there (who had not attended the briefing) also put his weight on the rope. That spectator quickly moved under the helicopter and applied his weight, reportedly about 80 kg, onto the rope.

The helicopter rolled rapidly to the right and began to go out of control. When it became evident to the persons on the rope that the pilot could not control the helicopter with both their weights applied, they both quickly let go and attempted to move away from under the helicopter. Although the casual pilot managed to get clear, the other person's ankle became entangled in the rope and he was lifted by the helicopter as it banked steeply right, (now out of control), and it proceeded to pivot 180 degrees to the right and move across the road towards a small service station, dragging the person below it by the leg.

One of the helicopter's main rotor blades struck the steel upright of a large illuminated sign; the helicopter then descended and struck the rear of a vehicle parked in front of the service station. The helicopter landed heavily beside this vehicle with its tail boom broken off but with its engine still running and main rotor still turning, causing major damage to the vehicle and multiple blade strikes to the building.

The pilot was winded in the accident, partly because the shoulder harness section of his inertia reel seatbelt had failed on impact. He managed, with some difficulty, to activate the emergency fuel cut-off to shut down the engine after unsuccessfully attempting to stop the engine by switching off the magnetos.

Spectators arrived to assist the pilot and passenger from the severely damaged cabin and to extinguish a fuel fire that had started below the ruptured left fuel tank.

The two occupants of the helicopter and the person caught by the leg by the abseiling rope all received minor injuries. The helicopter was destroyed and severe damage was caused to the service station buildings and the vehicle parked in front of the office. Although there were persons in the buildings when the helicopter crashed, none of them were injured.

The aircraft

The helicopter had been manufactured in 1970 and its data plate identified it as a Bell 47G-3B-2. It had been converted some time later to a Bell 47G-2A-1, although registration records show the type as a Bell 47G-3B-1.

Examination of the aircraft at the accident site and a search of maintenance records proved that the aircraft was suitably registered and that the maintenance release was current. No defects that would have affected the flight were apparent. The failed pilot's shoulder harness inertia reel was recovered for failure analysis.

The pilot was suitably licensed and endorsed on the aircraft type.

ANALYSIS

The Flight Manual for the helicopter type did not cover abseiling operations and there was no procedure for the attachment of ropes or lifting devices to the skid tubes in the manner used on the accident flight. There was no centre of gravity (cg) chart provided in the manual for loads attached to the skids. In normal operations, any loads that are to be suspended below the helicopter are attached to the purposely installed cargo hook mounted under the helicopter close to the cg. CSW was fitted with such a device which has both electrical and mechanical methods for instantly releasing the load when required, especially in an emergency.

The forward skid cross tube was about 780 mm forward of the optimal longitudinal centre of gravity and any load applied on a rope attached to it would cause the helicopter to pitch nose-down as well as causing it to roll to the right.

The Flight Manual for the Bell 47G series of helicopter has a section on loading of cargo litters (if installed) which states that the maximum load allowable on a litter is 102 kg. Litters are mounted fore-and-aft on the skid cross-tubes between the cabin side and the outside of the skid. An asymmetric loading chart is provided with the litter kit and is used for calculation of maximum allowable difference between loads on the left and right litters. As an example of the sensitivity of this type of helicopter to asymmetric lateral loads, if there is a passenger of 75 kg in the right seat, it is only possible to carry about 55 kg more on the right litter than on the left to remain inside allowable lateral cg limits. As the outside of the skid tube is several centimetres outboard of the litter centreline, any load applied at the skid tube would have a greater adverse effect on the lateral cg than the same load on a litter.

On the accident flight, the pilot was simulating an asymmetric load of about 150 kg (no load on the left skid tube, two persons hanging from the right skid), attached to the helicopter in such a manner that the lateral cg limits imposed by the manufacturer were exceeded. This lateral cg exceedance combined with a pitch-down of the nose as the load was applied, resulting in a loss of control.

The carriage of a passenger of about 80 kg in the right seat would have resulted in the helicopter being close to a laterally balanced condition before any load was applied to the rope. If it had been decided to conduct a proving flight after calculation of the lateral cg implications, the conditions would have been better simulated with no passengers in the cabin or with one occupying the centre seat. It would be expected that the person from the right seat would have been the one abseiling from the helicopter. A seating configuration which left the right seat empty would have reduced the exceedance of lateral cg experienced on the accident flight.

The two persons applying their weight to the rope attached under the helicopter released their hold when they realised the helicopter was not maintaining a steady hover. As one of the persons stepped backwards, his ankle became entangled in the rope. He was lifted by the helicopter then dragged up a bank onto a road. This dragging load, which could not be released from the aircraft in an emergency, probably prevented the pilot from regaining control before the helicopter struck the sign.

Although abseiling from helicopters is frequently carried out in military operations, the aircraft used are normally larger, cabin-class helicopters and it is possible for persons abseiling from the helicopter to do so from each side simultaneously, thus reducing the risk of an exceedance of lateral cg limits.

Investigation into the failure of the pilot's shoulder harness inertia reel revealed that the unit fitted to the helicopter was not approved for installation in Bell 47G aircraft type.

SIGNIFICANT FACTORS

The pilot was attempting to explore the effect on helicopter control of a lateral load applied to the outside of the right skid tube.

The lateral centre of gravity limitations of the helicopter were exceeded, resulting in loss of control.

The pilot was unable to regain control before impact with a sign when a person became entangled in the rope attached to the helicopter.

The pilot reported that the aircraft floated about half the length of the 1130 m strip before he decided to take the aircraft around for another circuit. When he retracted the third stage of flap, the left wing dropped, and the aircraft veered off runway heading. The pilot then lowered the nose of the aircraft in an attempt to increase air speed, but when he saw that a collision with trees was imminent, he closed the throttle. The aircraft ran through a boundary fence and came to rest among saplings about 100 m further. None of the three occupants were injured.

The emergency locator transmitted, installed in the rear fuselage, did not activate.