Ditching

History of Flight

The Kawasaki KH-4 helicopter was engaged in aerial work, spraying larvicide to control mosquitoes at Lake Joondalup in Perth's northern suburbs. The crew consisted of the pilot and an employee of the local city council who was directing the pilot on where to spray. The city council employee occupied the right passenger seat.

The spray runs were being conducted at an altitude of about 30 ft to prevent the pesticide from drifting excessively. The runs started at the east side of the lake, track crawling towards the west. The tracks of each run were orientated approximately north/south, aligned with the shoreline. The pilot reported that turbulence made the helicopter progressively more difficult to control in maintaining speed and height the closer the tracks came to the western side of the lake.

The helicopter had conducted three spray runs during the previous hour without incident. The fourth and final planned run was to cover the western shore area of the lake. While the helicopter was conducting a right procedure turn to track into north, it descended and hit the water. The helicopter came to rest in shallow water almost upright and slightly nose-up. It later rolled onto its right side. The pilot exited the helicopter unimpeded and the passenger released herself from her lap belt. She chose to stay in the helicopter until medical help arrived because she was concerned that she may have sustained a back injury.

Terrain

Lake Joondalup was oriented north-north-west and located in a small valley approximately 5.4 km east of the coast. High ground to the west of the accident site rose to a height of 70 m within 700 m. The ground to the east was more undulating, rising to a height of 100 m within 3 km. To the north-west of the lake were several small saddles. The high ground immediately to the west was a built-up area of residential housing and along the shore were trees to a height of about 6 to 10 m.

Weather

The weather at the time included 3 octas of cumulus cloud at 3,500 ft and 5 octas of strato-cumulus cloud at 4,500 ft. The temperature was 18 degrees Celcius. The wind at Perth airport, 25 km south-east of the accident site, was north-westerly at 14 kts gusting to 21 kts. The wind recording at Ocean Reef, the closest Bureau of Meteorology (BoM) facility to the accident site, was north-westerly at about 10 kts gusting to 13 kts. The Ocean Reef BoM facility was 6 km west of the accident site.

Witnesses at the site described the wind as being north-westerly and blustery with intermittent strong wind gusts.

An assessment of the terrain and wind conditions conducted by the BoM concluded that due to the trees and steep slope to the west of the lake, the wind flow over the area could have been disturbed and that, as a result, turbulence may have developed at the accident site. The BoM reported, however, that the degree of turbulence could not be determined due to the lack of recorded or observational data.

The investigation was on-site within 30 minutes of the accident. The wind was noted as being north-westerly at about 10 kts and gusting to an estimated 20 kts.

Personnel Information

The pilot had a total flying experience of about 724 hours, including 640 hours gained on the Bell 47/KH-4 helicopter types. Although the pilot had completed low-flying training and had acquired about 60 hours in low level operations including survey work, he had no experience in agricultural flying. He had completed a mosquito spraying operation without problems about 8 months prior to the accident. The operator reported that the pilot had conducted most of his low flying operations in relatively benign wind conditions. The pilot complied with the experience requirements under the exemption granted by the Civil Aviation Safety Authority (CASA) for the operator to conduct this particular type of work.

Helicopter Information

The helicopter was a Kawasaki KH-4 which at the time of the accident was within all-up-weight and centre-of-gravity limitations. The KH-4 cockpit/cabin was configured with a centre forward seat that was occupied by the pilot. Three passenger seats were located at the rear of the cabin, just aft of the pilot's seat. Two hoppers, one mounted on each side of the helicopter, were fitted for the disbursement of the dry granulated pesticide. The pilot reported that he was using a power setting of about 32 inches (Hg) Manifold Air Pressure (MAP) to maintain 30 kts groundspeed downwind during the wind gusts and about 25 inches to maintain a similar speed when flying into wind. The take-off (2 minutes) power limit was approximately 33 inches and maximum continuous power was about 28 inches. The maximum power permitted was 36 inches MAP. Flight manual data indicated that the helicopter should have been capable of achieving a rate of climb of nearly 1,000 ft per minute using take-off power at 39 kts.

Turbulence

As wind blows around and against obstacles such as trees, fences and buildings, the smooth flow breaks into a series of irregular, twisting, whirling eddies. These eddies are produced by mechanical turbulence and may rotate about axes in any direction. Mechanical turbulence tends to be lower over relatively smooth ground. The area upwind of the accident site was not smooth due to the trees.

Stronger winds usually produce more and larger eddies, and therefore more turbulence. Eddies could produce downdraughts that would cause a helicopter to lose height. In response, a pilot would need to increase the collective pitch to maintain the helicopter's height above the ground. Turbulence may also adversely affect the aerodynamic efficiency of the helicopter's main rotor blades, reducing the lift being produced by the main rotor system. As a consequence, flying in areas of turbulence usually requires more power to maintain a helicopter's height above the ground.

The adverse effect of turbulence may also be magnified if the helicopter is manoeuvring because the lift being generated by the main rotor system is being tilted away from the vertical. Therefore, only a percentage of the lift being produced by the main rotor is being used to counteract the effect of turbulence.

Flight profile

The pilot reported that he had completed a south-orientated track of the final run and had planned the right procedure turn to roll out heading approximately north. The procedure turn involved turning the helicopter to the left before commencing a right turn. This technique reduced the spacing between tracks. The pilot reported that while the helicopter was in the climbing banked turn to the left, he had flown it to a height of about 50 ft. Once he was sure of maintaining a suitable distance from the west bank of the lake, he commenced the right turn to align with the northerly track. He reported that during the turn to the right, he felt the helicopter begin to sink, so he lowered the nose to accelerate and continued the turn into wind. He also reported that at the time the wind was gusting. The pilot further reported that he felt the helicopter skidding in the turn as it descended below the tree height and he raised the collective and introduced power to arrest its rate of descent. However, the helicopter continued to sink and, realising that he would not be able to complete the turn into wind, he began rolling the helicopter to a wings-level attitude. The observer reported that she thought that the helicopter was "banked right over" and that during the turn, she could feel herself being pushed into her seat. She thought the bank angle was more than she had previously experienced during the morning. The pilot reported that he thought that the bank angle did not exceed 30 degrees.

The pilot reported that he continued raising the collective and introducing power. He reported that he did not over-pitch the main rotor and main rotor RPM remained within limits until the helicopter hit the water. When the helicopter skids hit the water, the helicopter spun through about 180 degrees and came to an abrupt stop. When all motion stopped, the pilot was still seated and restrained by his four-point harness. The observer reported that she thought that she had been pushed against the cabin roof during the impact although she was still firmly restrained by the lap harness after all motion had stopped.

Wreckage Information

The helicopter had come to rest approximately 50 m from the lake's western shore and about 550 m south-south-west of Lake Island. Damage to the main rotor system was consistent with the blades hitting the water under power. Witnesses reported hearing the engine operating immediately before the helicopter hit the water. No pre-existing mechanical fault in the helicopter was found.

The helicopter was being operated in accordance with operator's operations manual and the exemption granted by CASA. Although the pilot was qualified in accordance with requirements in the operations manual, he had no flying training in agricultural operations and was relatively inexperienced in low-level flying operations in adverse wind conditions. There appeared to be no pre-existing mechanical fault that contributed the accident.

During the three spray runs prior to the accident, the helicopter had been positioned towards the eastern side of the lake. The pilot had been conducting the runs approximately north/south and paralleling the shoreline, using the procedure-turn technique to reposition the helicopter for each run. The spray runs were being conducted at a height of about 30 ft with a climb to about 50 ft during the procedure turns. While the helicopter was experiencing some turbulence on the eastern side of the lake, the pilot noted that the turbulence was becoming more pronounced as he worked the helicopter westward. The lower level of turbulence experienced on the eastern side of the lake was consistent with mechanical turbulence dissipating over the smooth open water. In benign wind and turbulence conditions, the reported power margin would normally have been adequate for the task.

While the recorded wind conditions at the nearby Ocean Reef BoM station were quite benign, reports from the accident site indicated that the wind was blustery, and the strength of the gusts appeared to be significantly in excess of those being recorded at Ocean Reef. The lake's north-north-westerly orientation and high terrain to the west possibly increased the wind strength in the local area. The built-up area and vegetation along its western shore possibly induced wind eddies and considerably turbulent conditions near the lake's western shore.

The increasing level of turbulence being encountered by the pilot should have served to indicate that caution was required. Despite the increasing turbulence the pilot did not consider flying the helicopter higher above the water to provide a greater margin for regaining height should the helicopter be affected by the turbulent conditions. Rather, the pilot appeared focused on positioning the helicopter to ensure the spray coverage and to maintain a safe distance from the shoreline and trees. When the pilot banked the helicopter to the right, the evidence was consistent with it entering an area of strong turbulence, which caused the helicopter to unexpectedly descend towards the water. Although the reported power margin would normally have been adequate to effect a recovery in benign conditions, due to the lack of recorded information, the investigation could not determine if the power margin was adequate to overcome the conditions encountered by the helicopter at the time. Also, the pilot may not have used full power to recover from the descent. By the time the pilot realised that the helicopter was descending at an excessively high rate, there was insufficient height available for him to effect a recovery before the helicopter hit the water.

The helicopter's manoeuvring at a low height above the water, local weather conditions and the pilot's lack of experience in low-level operations in adverse wind conditions were probably all factors that contributed to the accident.

The helicopter's operator reported that the procedures and experience requirements for conducting low-level operations were being reviewed.

The pilot was assisting in flood rescue operations and was directed to a homestead where several people had climbed onto its roof to escape from the fast-flowing flood waters, which had risen to the height of the roof line.

He approached the homestead at a height of about 2m above the water level, then hovered the helicopter alongside the roof to allow an elderly person to board. This person had had a safety rope attached to him to prevent him from slipping off the steeply pitched roof. As he climbed onto the skids his weight moved the helicopter slightly sideways, and the rope snagged on the roof causing the helicopter to descend. The pilot was unable to arrest the downward movement in the height available before the helicopter struck the water and sank.

All occupants escaped, the pilot recovered the ELT and activated it.

After conducting 15 joy flights from the Geelong helipad from about 1145, the pilot flew two passengers on an advertising project. One of the passengers, a local radio announcer, was tasked to perform a live radio cross from the helicopter.

On the commencement of the last approach to land to the south-east, the pilot estimated the wind to be 15 kts from the north-west. He advised that when on short final, 200 metres from the helipad, he noticed a sudden wind shift and the helicopter experienced loss of lift. He increased throttle and collective in an attempt to maintain height and reach the helipad. However, rotor RPM decayed and the helicopter settled into the sea 60 metres short of the helipad.

Subsequent viewing of amateur video footage showed the latter part of the landing approach to be very shallow, followed by a classic example of overpitching with the main rotor disc coning and the RPM audio decreasing as the helicopter descended into the sea.

No fault was reported with the airframe or engine which may have contributed to the accident.

During initial climb after take-off from Wynyard the engine suffered a power loss. The pilot observed the manifold pressure decreasing so he selected alternate air, checked the mixture control was set to rich and checked the fuel pump was switched on. He changed the fuel selection from the left tank to the right tank, but the engine did not respond. By this time the aircraft was low over the water, so the pilot transmitted a PAN call advising of the emergency and his intention to try to land on a beach. When the aircraft had descended to about three metres above the water and its speed had decayed to 60 knots, the pilot broadcast a MAYDAY call. Shortly afterwards the aircraft was stalled into the water at the mouth of the Inglis River. The impact forces broached the fuselage which rapidly filled with water. The pilot and his two passengers evacuated the aircraft before it sank and were rescued by the crew of a nearby fishing boat.

The investigation into the cause of the engine power loss was hindered because the aircraft was badly damaged during the accident and the subsequent recovery exercise. It was established that sufficient fuel was on board for the proposed flight and fuel was available to the fuel distributor, but the contents of the fuel filter assembly could not be determined.

The engine was inspected and disassembled, and relevant components were tested. It was found that the air duct hose fitted between the air filter and the fuel control unit was collapsed due to disbonding of the internal supporting wire. It could not be determined if this had occurred prior to the ditching and was the cause of the power loss or had occurred due to the forces/pressure of the water in the engine bay during the ditching.  No other anomalies were found that could have caused the power loss.

The air duct hose was one that is commonly called a 'SCAT' hose and was made up of a single layer of neoprene impregnated fabric material supported internally by a spring steel helix wire bonded to the fabric.  This SCAT hose is not approved by the manufacturer for this installation. The correct hose carries the manufacturer's part number and is constructed of a 2-ply silicone resin impregnated with woven fibreglass which is bonded and cured along with an inner liner and tabbed ends to facilitate retention. It is also wire reinforced with galvanised hard temper spring steel.

The manufacturer of the SCAT hose has recently changed the specification for these hoses to say that they are 'not recommended for negative pressure applications'. Many aircraft have SCAT or similar hoses fitted to negative pressure engine intake systems, as was the case with this aircraft.

Significant factors

1. It is suspected that the SCAT hose collapsed reducing the inlet air supply to a level that precluded the engine from delivering full power.
2. The SCAT hose was not the hose that was designated by the manufacturer to be installed in the air inlet system.
3. The pilot was forced to ditch the aircraft into water.

Safety action

1. Information on engine intake hose installations is available in an article 'SCAT/SCEET hoses linked to engine failure' published in the CASA Flight Safety Australia Summer 1997 issue.
2. CASA advise that a program is being developed to examine the ramifications of the widespread use of SCAT hoses in engine negative pressure air inlet systems.

FACTUAL INFORMATION

Following a normal climb, the pilot dropped two parachutists over Hamilton Island. A power-off descent to circuit height followed. The pilot did not select Carburettor Heat during the descent. When on a long final approach, the pilot attempted to arrest a high descent rate with the use of engine power. The engine failed to respond. The pilot found that the aircraft was outside gliding range of the runway and he decided to ditch the aircraft in shallow water. Engine trouble checks failed to restore power to the engine.

The aircraft was ditched in shallow water and after a successful escape from the cabin, the pilot was picked up by an island launch.

The aircraft's engine was transported to a maintenance facility at Archerfield where it was examined. The engine was extensively corroded by salt water. No fault was found as far as could be determined.

The Bureau of Meteorology data showed that the relative humidity at ground level was 65%. The Carburettor icing - probability chart showed that serious icing at descent power was to be expected at such a humidity level.

ANALYSIS

Although there are other possible reasons for the power loss, it is most likely that the engine failed to produce power due to carburettor icing.

The pilot reported that he was operating at 500 feet above the sea taking photographs of a friend's boat. He experienced a sudden onset of severe engine vibration. Because of the severity of the vibration, he believed that the engine may break its mounts. He shut the engine down immediately and ditched close to his friend's boat. He was rescued from the wing of the aircraft which sank shortly afterwards in approximately 60 fathoms of water.

The cause of the engine vibration was not determined but the pilot said the severity of the vibration was what he imagined would be consistent with the loss of part or all of a propeller blade.

The aircraft took-off normally but climbing through about 400 ft it suffered a sudden, complete engine failure. The pilot carried out emergency procedure checks, which included changing from the left fuel tank to the right, but when this failed to immediately restore power he changed back to the left tank and pumped the throttle vigorously without success. The pilot then carried out a forced landing into the sea adjacent to the shore. All occupants evacuated the aircraft uninjured.

The aircraft had been refuelled the previous day to its maximum capacity of 330 litres and then flew for 2.3 hours. The pilot then dipped the fuel tanks which showed 170 litres of fuel remaining. The next morning, he did not recheck the fuel quantity using the dip stick but relied on the fuel gauge readings which at times are inaccurate. These indicated 40 litres in the left tank and 80 litres in the right. The aircraft then flew for another .6 of an hour using the left tank. The engine failed during the next take-off.

An inspection of the aircraft revealed that the right tank contained fuel, but the left tank was empty. The fuel consumption rate was advised as being 70 litres/hour.

The pilot had not selected the tank which indicated the greater quantity of fuel for take-off, and when the engine failed he changed from the left tank to the right, but did not wait long enough for air to expel from the engine fuel feed line to allow resumption of fuel flow from the right tank to the engine. Pumping the throttle would not have had any effect on regaining power as the engine is fuel injected.

The pilot reported that the engine failed during cruise at 8,500 ft. The aircraft was over water and a glide towards the coast was initiated. Aircraft ditched in the Gulf of Carpentaria. Both occupants were rescued by SAR helicopter at about 2200. The aircraft wreckage was not recovered and no indication as to the cause of the engine failure could be determined.

The joy-flight was proceeding northwards over the beach of Surfers Paradise and had been cruising at 500 feet for just over a minute when the engine power reduced to idle. After conducting his trouble checks and finding no way to restore power the pilot selected an area for a landing on the beach. The aircraft came to rest in shallow water after manoeuvring to avoid people on the beach.

On inspecting the engine area, the pilot found that a ball joint in a push-pull rod to the carburettor throttle valve had failed, allowing the throttle to close. Further examination by the maintenance organisation revealed that a plate to which the rod was attached was shaped incorrectly. This caused the spring-loaded ball joint to wear abnormally until it fell off. The engine had been overhauled 200 hours earlier.

The pilot left Canberra for Moruya with 70 litres of fuel on board which he reported was evenly distributed in the two wing tanks. He flew to Moruya with the left tank selected and reported that the flight took 40-45 minutes. After a brief stop at Moruya he taxied for the return trip. Pre-take-off checks were completed while taxiing, one of the final checks being selection of the right wing tank for the return trip.

The taxi route involved back-tracking along the main north/south runway. As there were two other aircraft inbound, one of which was already in the circuit for runway 18, the pilot expedited his taxiing and decided to take off using approximately 1000 metres of the 1523 metre runway. He made a left turn on the runway and immediately applied take-off power. Shortly after the aircraft became airborne the engine stopped.

The pilot established the aircraft in a glide and landed it in the water in the Moruya River. The cause of the engine failure was not determined.