The pilot reported that the helicopter landed heavily in a carpark, after the engine lost power during takeoff. On lift-off, engine indications were normal with 28-29 inches boost while in the hover. As the helicopter accelerated, the pilot felt a deterioration in performance and observed that the boost had fallen to 15-18 inches. During the subsequent landing, the helicopter's main rotor blades struck a tree and both landing skids were bent. The helicopter remained upright. Post flight examination found that the turbo charger had failed.

FACTUAL INFORMATION

The B737 had departed from Melbourne on a flight to Cairns, Qld, two minutes ahead of the B747 on the same route. Both aircraft were climbing to an initial altitude of flight level (FL) 200 and the crews had been approved to vary their climbing speed. The crew of the B737 increased their speed to 300 knots and the crew of the B747 were approved to conduct a "high speed climb". Due to an active restricted area, both aircraft were given a radar vector to take them off track and jurisdiction for the flights was transferred to the Inner North controller. Both crews contacted the Inner North controller whilst on a heading of 010 degrees, with the B747 paralleling the track of the B737 to the right with approximately 8 - 10 NM separation.

The closing speed at the time of the transfer was approximately 50 knots. The B737 was then cleared to climb to flight level (FL) 310 and the B747 to FL390. When the aircraft were clear of the restricted area, the controller issued instructions for both crews to track from their respective positions direct to the reporting point TOBOB, at which they were to intercept their planned route. The planned track to TOBOB was approximately 355 degrees and the instruction would result in a turn of approximately 20 - 25 degrees to the left for both aircraft. The controller did not realise that the second aircraft was a B747 and thought it was an aircraft of a lower performance. He was not familiar with this type of aircraft on this route and, although he knew that the registration belonged to a B747, did not reconcile that particular type with the traffic situation.

The wind was from the north-west, with forecast speeds of 70 knots at flight level (FL) 185. The crew of the B737 were the first to turn their aircraft in accordance with the controllers instructions and chose an initial heading that was to the north-west and directly into wind. This turn had the effect of reducing the ground speed by almost 60 knots. The turn was approximately 55 degrees, more than that required to track direct to TOBOB, and an adjustment was made about 1 minute later. Because of the position of the B747 relative to the B737, its turn of approximately 20 degrees resulted in a more northerly heading and, as such, the reduction in its ground speed was less than 10 knots.

These changes resulted in a significant increase in closing speed at a time when the Inner North controller became occupied with other work-related tasks. Consequently, he did not initially notice the reduction in separation. Shortly after, as he conducted a scan of his area of responsibility, he saw that the B747 was closing rapidly on the B737 and that there was less than the required vertical separation with the B747 below. He immediately attempted to achieve vertical separation by instructing the crew of the B737 to maintain FL210. The intent was to allow the B747, which had a greater rate of climb, to achieve the necessary vertical separation before the horizontal separation standard was infringed.

However, it became obvious that this plan would not achieve the objective and he issued a radar vector to the crew of the B747 in order to maintain radar separation. Before the distance between the aircraft started to increase, the horizontal separation had reduced to 4.2 NM while vertical separation was 200 ft. The required standard was either 5 NM horizontally or 1,000 ft vertically. A breakdown of separation had occurred. Examination of the radar data indicated that the closing speed had increased to 160 knots for a short period prior to the radar vector taking affect.

SIGNIFICANT FACTORS

1. The Inner North controller assumed that separation would be achieved through differences in aircraft performance without employing separation assurance techniques.

2. The crew of the B737 executed a turn which was greater than that expected by the controller.

3. The Inner North controller did not immediately recognise the combination of events that led to a significant increase in closing speed.

The pilot was attempting the first take-off from a grass paddock on an agricultural operation. Take-off direction was towards the west with 700 m of ground roll available. The wind was variable, but mainly a gusting crosswind from the right at around 10 kt. The aircraft was below maximum weight with a full hopper load and about half fuel.

When it became evident that the aircraft would not lift off by the end of the available take-off area, the pilot rejected the take-off and attempted to stop in the paddock remaining.

The aircraft veered to the left, collided with a fence and ground-looped before coming to a stop.

The pilot reported that engine operation was normal, and he was unable to explain why the aircraft did not lift off in the distance available, which should have been adequate. He believed the changing wind strength and direction may have been a factor.

The Aerostar was being flown on a passenger charter flight from Maitland, NSW to Olympic Dam, SA. Arriving in the circuit area, the pilot reported that he observed the windsock indicating a surface wind of 240 degrees at 10 knots. However, because the runway length of 1591 m was more than adequate, he elected to land on runway 06 with a tailwind component. He said he flew a normal approach using 45 degrees of flap, touching down about 150 m beyond the landing threshold. 

Shortly after touching down the aircraft was struck by a strong wind gust and diverged to the left. The pilot was unable to prevent the aircraft from departing the sealed runway surface and entering an area of soft earth. The right main landing gear collapsed, and the right propeller struck the ground, stopping the engine. After the aircraft had stopped, the pilot shut down the left engine and evacuated the two passengers. Nobody was injured.

A local pilot who arrived at the site shortly after the accident estimated the wind as 240 degrees at 25 to 35 knots, but with regular gusts from the north. He also reported that the wind conditions had been similar all morning. The pilot of the Aerostar subsequently reported that local pilots said that the terrain around the landing area can produce a wind funnelling effect along and across the runway, which may not have been readily apparent.

A significant factor in this accident was the decision of the pilot to land on a runway affected by a marked downwind component.

The date and timing of the occurrence are approximate only.

The aircraft was being used, on behalf of Airservices Australia, to conduct air tests on the static-line used with the PADS supply dropping system. A flat-strap static line, with a cone attached, was trailed behind the aircraft and its movement observed on a video camera. The tests indicated that the line could oscillate severely under certain conditions. On one of the test flights the line oscillated until it collided with the rear fuselage. The aircraft was not damaged, and its flying characteristics were not effected. The line was pulled in and a normal landing completed.

As a result of the tests, the flat-strap line was replaced with a round line and the cone modified. Subsequent tests indicated that this configuration was stable, and the oscillations were not repeated.

While taking off for parachute dropping operation, directional control was lost and the aircraft ground looped. The left main landing gear collapsed, substantially damaging the aircraft. All six occupants evacuated the aircraft without injury.

The pilot subsequently reported that, as take-off power was applied, the aircraft started to swing to the left. He applied right rudder to correct the swing, but the aircraft then swung rapidly to the right. He was unable to counteract the swing and closed the throttle to stop the take-off. However, the left wheel ran into a culvert and was torn off before the aircraft could be stopped.

The pilot reported that he was conducting a practice forced landing when the engine stopped. At 3,000 ft he had applied full carburettor heat, closed the throttle and commenced a glide descent. During the descent he applied power on four occasions to re-warm the engine. At about 600 ft AGL the engine stopped along with the geared wooden propeller. The pilot carried out trouble checks and declared a Mayday. He twice engaged the starter in an attempt to restart the engine but was unsuccessful. He subsequently reported that the starter seemed to be sluggish.

The aircraft touched down in a paddock on a downhill slope. It rolled about 30 metres, crashed through a farm fence, passed under a powerline, crossed a road, encountered a ditch and overturned.

At the time of the accident weather conditions were: CAVOK, outside temperature about 15 degrees Celsius, wind calm, visibility 10 km plus, nil precipitation.

This was the second accident to VH-IDB in the same area due to the engine stopping during practice forced landings. The previous accident occurred on 14 May 1997. Verbal reports of other instances have been received of Skyfox Gazelles experiencing engine stoppages after the throttle was closed and engine RPM reduced to idle.

After the first accident, the engine was inspected by a licensed aircraft maintenance engineer (LAME). Then, after the second accident with the same engine installed, it was inspected first by the LAME and then by the engine manufacturer's agent. No fault was found with the engine after each accident. Post accident tests on the starter, the battery and the engine have failed to detect a reason for the sluggish starter anomaly reported by the pilot.

Safety Action

As a result of complaints about the stalling of engines at idle, Airworthiness officers from the Civil Aviation Safety Authority (CASA), in conjunction with the aircraft manufacturer, conducted an investigation which included test flights in the Gazelle.

It was found that the throttle mechanism had enough free play (also known as backlash) to reduce RPM below idle and stop the engine. This could occur if extra force was applied when pulling the throttle back to idle speed. To address this problem, the aircraft manufacturer issued Service Bulletin (SB) No. 20 on 28 October 1997. This SB provides the following information: "Idle speed may inadvertently be reduced below set minimum due to incorrect throttle stop adjustment." SB 20 requires operators to check the idle setting and adjust for backlash at the throttle stop in the cockpit. Compliance was mandatory, within two weeks or 10 hours time in service from receipt of the SB.

VH-WNZ was conducting a training flight, and the pilot had advised the Tower of his intention to conduct a simulated engine failure after take-off. The aircraft departed on an initial assigned radar heading of 060 degrees at 1710.40 EST.

VH-OGK was assigned an IBUNA 1 Standard Instrument Departure (SID), departed at 1712.30 EST, and had been instructed to remain on Tower frequency. While turning right as per the SID to heading 180 M, OGK passed behind WNZ. Separation between the aircraft reduced to 2.5 NM horizontally and less than 500 ft vertically. The required separation was 3 NM and 1,000 ft.

Investigation revealed that the aerodrome controller (ADC) did not adequately plan the departure of three aircraft, including WNZ and OGK. An arriving aircraft led to his decision to expedite the departure of OGK, thus compromising the separation between these aircraft. The ADC's decision to retain OGK on Tower frequency until instructed to transfer delayed the opportunity for the departures controller to issue instructions to OGK to ensure separation was maintained.

The pilot stated that while hovering the helicopter at about 50 ft over a dry riverbed, the engine note suddenly changed. He checked the instrument indications which confirmed that the engine RPM had increased. Almost immediately the indications returned to normal. He began to move the helicopter away from trees when the engine RPM again increased as drive to the main rotor system was lost.

During the attempted autorotational landing, the helicopter collided with a tree and landed heavily on the riverbank.

While vacating the helicopter, the pilot became aware of a "rumbling" noise and smoke coming from under the cabin. He attempted unsuccessfully to locate the source of the noise by isolating the electrical systems. He then switched off the battery.

Output from the helicopter engine is coupled through a V-belt drive system to the main transmission which drives the main rotor, and to the tail rotor drive system. The belt drive clutch control installation includes a linear actuator and electrical connections to a clutch control switch and warning light on the instrument panel. A cable and pulley interconnect the linear actuator to the clutch spring on the belt drive transmission. The clutch control switch, which is positioned on the lower left side of the instrument panel, has three positions, RELEASE, HOLD and ENGAGE (the normal operating position). With the switch in the ENGAGE position, the linear actuator retracts, applying tension through an idler pulley to the V-belts. The clutch warning light is on unless the clutch is fully engaged.

Examination of the helicopter rotor drive system did not identify any pre-existing defect which may have contributed to the accident.

The "rumbling" noise heard by the pilot was caused by the starter motor operating due to impact damage to the solenoid. There was no fire.

The linear actuator shaft was found to be extended by approximately 30 to 50% of its travel. It is normally fully retracted when the drive belts are correctly tensioned. The actuator, the clutch control switch, the clutch warning light and the associated wiring were tested and found to be serviceable. It was not possible to determine if the warning light was powered at the time of impact. The position of the linear actuator shaft may have changed following the accident when the pilot repositioned various switches and circuit breakers in an attempt to identify the "rumbling" noise.

The clutch control switch was fitted with a guard to prevent inadvertent operation. However, the retaining springs had weakened such that the guard was ineffective.

The circumstances of the accident are consistent with loss of rotor drive due to insufficient drive belt tension. However, the circumstances in which this occurred could not be determined.

The hot air balloon had taken off from Picton on an early morning joy flight to Camden. Surface wind conditions were calm, with a south-westerly wind of 24 kt at 1,000 ft. Surface winds were not expected to increase before late morning.

The pilot in command reported that the flight proceeded as planned, and a normal approach was made for a landing on Camden aerodrome. The surface wind was 5-8 kt. Some 200 m from the landing point, at a height of about 50 ft, the rate of descent began to increase more than required. The pilot activated two burners for about 5 sec to arrest the descent. As expected, the balloon flew level for a short distance, then unexpectedly began to climb rapidly. The parachute valve was opened to counteract the climb, which stopped at about 200-250 ft. However, the balloon then began to descend rapidly. All burners were turned on in an attempt to arrest the descent, but to no avail. The balloon impacted the ground at an estimated rate of descent of 600-700 fpm.

The rapid deflation system was operated just before impact, but the balloon was dragged across the ground for about 30 m before becoming airborne again, reaching a height of about 20 ft before again contacting the ground and being dragged a further 40 m. As the balloon came to a halt the pilot reported that the deflated envelope flapped in the breeze for some time, suggesting an increase in the surface wind.

One lady sustained a fractured ankle during the landing. The other twelve occupants were uninjured.