Collision with terrain

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.

The pilot was spraying crops adjacent to the Leigh River. The river meanders through a steep sided valley oriented approximately north-south, with the crop being sprayed located above the west ridge of the valley. The pilot advised that he had refuelled the aircraft and refilled the hopper.

The wind was gusting from the south-west and he was on a spray run, tracking to the south, at 5 ft above the ground, when a gust of wind caused the left wing to drop. The pilot advised that he was unable to stop the wing hitting an embankment and the aircraft rolled into the valley, coming to rest upright, substantially damaged and burning.

The pilot suffered a broken ankle and burns but was able to extricate himself. The aircraft was destroyed.

The helicopter was being flown in support of geological drilling operations and had just been used to externally sling-load a pump into a creek bed. The refuelling point and landing area were located about 20 m from the edge of a ravine which was approximately 30 m deep and 100 m wide. A tree was growing from a point below the top of the ravine and the tree's tops protruded approximately 3 m above the ravine's edge. When the pilot flew the helicopter to the landing area to refuel, he lowered the external sling to the ground and then flew the helicopter backwards approximately 1 m, intending to land next to the fuel drums.

As the pilot was landing the helicopter, evidence indicates that the left skid became caught on a rock. When the pilot attempted to fly the helicopter clear, the left skid suddenly broke clear of the rock. The helicopter rolled right as it climbed, and the right skid impacted a pump housing protruding from the top of a fuel drum before striking the top of the tree located on the ravine's edge.

The helicopter continued drifting and began yawing right as it descended into the ravine. The pilot reported that just as he was regaining some control of the helicopter, it landed, upright, on a rock shelf approximately 2 m from the ravine floor. It appears that at this stage, the main rotor impacted the helicopter's tail boom. The helicopter then rolled and fell off the rock shelf to the ravine floor. It came to rest on its right side with the engine still running and main rotor turning.

The pilot reported that he then closed the throttle, turned the fuel switch off and exited the helicopter through the front windscreen, having suffered minor injuries. He also reported that he turned off the emergency locator transmitter beacon although it did not appear to be operating.

During the landing, evidence indicates that the left skid became stuck in the rock. When the pilot attempted to reject the landing, it is likely that he would have used a combination of up collective and right cyclic as the helicopter pivoted around the left skid. It appears that the rock then broke. The sudden release of the left skid, associated with the cyclic and collective control positions probably caused the helicopter to rapidly roll and drift right. As the helicopter climbed, rolled and drifted, it was likely that the pilot could not have quickly regained control due to the subsequent impacts with the fuel pump and tree. It was probably fortunate that the helicopter entered the ravine, giving the pilot time to recover some control before the landing on the rock ledge. The forces and imbalance generated by the main rotor strike on the tail may have then caused the helicopter to rollover, fall off the shelf before finally coming to rest on the ravine floor.

The pilot was conducting a charter flight from Moorabbin to French Island and return. He was carrying 3 passengers with light luggage. On arrival at French Island, he landed to the east on the grass strip. While taxying after landing the nose wheel became bogged in sandy soil near the eastern end of the airstrip. The pilot shut down the engine and the passengers helped him push the aircraft to a parking position facing west at the eastern end of the strip. This location enabled the pilot to use the full length of the grass strip for a take-off to the west later in the day. Later, when the group returned to depart the outside air temperature was approximately 14 degrees Celsius, the wind was calm and the QNH was approximately 1021 mb.

The airstrip surface was slashed grass and much of the soil underlying the grass surface was sandy loam. In the take-off direction the strip was slightly up hill until about midway, and then slightly downhill. The airfield was approximately 131 ft above sea level and the surrounding terrain was gently undulating. The pilot applied full power and held the aircraft on the brakes before commencing the take-off roll. The passengers reported that the aircraft accelerated normally for about 100 metres, after which the rate of acceleration slowed. As the aircraft neared the western end of the strip and the pilot rotated the aircraft to become airborne the passengers advised that they heard a noise which they believed was caused by the tail of the aircraft striking the ground. The pilot did not recall a noise as the aircraft rotated but said that he noticed a slight change in engine note soon after liftoff.

The aircraft climbed to about 20 ft, banked slightly left and then settled back onto the ground approximately 70 m from the point of lift-off. It skidded down a gentle slope through light foliage and logs, slewed to the left and came to rest about 135 metres beyond the end of the strip. As the aircraft stopped, the pilot and passengers saw flames in the cabin. The pilot's door had jammed shut because of fuselage damage, therefore all occupants evacuated quickly through the right door. Within seconds the aircraft was engulfed in flames. None of the passengers reported hearing the stall warning horn at any stage. They reported that the engine sounded as though it was producing take-off power even after they heard the tail hit the ground. Although the aircraft was substantially damaged by fire no pre-existing fault was found with the aircraft.

Because of the fire damage, the stall warning system could not be tested. The maintenance release was issued for operation in the aerial work category which did not embrace the requirements for this charter flight. The pilot reported that he had selected 1/4 flap for the take-off. The flaps were found in the up position after the accident; the flap selector may have been knocked up during the impact. The pilot estimated that the take-off weight was 1006 kg, which included 36 litres of AVGAS. Subsequent calculations showed that the take-off weight was 1017 kg, which was 49 kg below the maximum allowable weight. The pilot reported that he had checked the aircraft performance data before the flight and assessed that a 600-metre strip would be adequate for taking off over a 50 ft obstacle in nil wind conditions. None of the performance charts included factors for degradation of aircraft performance due to wear and tear, or for the slowing affects of sandy loam underlying a grass surface.

The operator reported that prior to conducting charter operations on French Island, two company pilots had measured the strip using vehicle odometers and recorded a length of 600 metres in the company's authorised landing area register. Using a calibrated wheel after the accident, the strip was re-measured and found to be only 500 metres long.