The operator and pilot reported that the helicopter struck a single-wire-earth-return (SWER) power line at the beginning of a swath run during a spraying operation. The orientation of the cane paddock being sprayed was north-east / south-west with a major power line running through the north-eastern corner. A SWER power line running east -west joined the main power line over the paddock. The pilot had sprayed the western edge of the paddock, flying the helicopter over the main power line on each spray run. As the pilot moved his spray effort further east on each swathe run, he concentrated on missing and flying over the main power line. On one pass he lost awareness of the SWER line and during descent onto the crop the mast of the helicopter struck the line. The helicopter rolled into the crop. The pilot was not injured

FACTUAL INFORMATION

At 0450 WST, the Bell 206 helicopter departed the heliport on East Intercourse Island to conduct a marine pilot transfer to a ship waiting at the outer buoy in Dampier Sound. The pilot reported that although there was a high overcast, which mostly obscured the moon and made the sky very dark, the horizon was visible. The towns of Dampier and Karratha were to the south-east of the ship. The wind was calm and the sea surface almost mirror-like. The pilot reported that the horizon was clearly discernible during the transit to the ship. The moon set at 0452 and sunrise was at 0633. The helicopter landed on the ship at about 0505 and disembarked the marine pilot. At about 0514, the helicopter departed towards the north-east. The pilot reported that as the helicopter climbed through 500 ft, the tail rotor pedals felt unusual. Whilst he was attempting to determine the nature of the tail rotor pedal problem, he did not monitor the helicopter's flight attitude and performance, and the helicopter descended into the sea. A deck hand on the ship reported to the ship's bridge staff at about 0515 that he saw the helicopter's lights enter the water off the ship's port side. At approximately 0615, a port authority vessel recovered the uninjured pilot. The helicopter sank in about 18 m of water in the main shipping channel to Karratha.

An inspection of the recovered wreckage did not reveal the cause of the reported fault in the tail rotor control system. The pilot reported that although the pedals had felt unusual, there had been no loss of directional control before the impact.

The helicopter was fitted with a radio altimeter that had a low height alert warning light. The pilot reported that the alert was set to activate at 150 ft but did not recall seeing the low light illuminate before the helicopter struck the water. The helicopter was not fitted with an autopilot or height hold facility. The operator reported that the collective of the helicopter had a tendency to fall if not closely controlled by the pilot.

The pilot had recorded approximately 4,200 hours flying experience on a variety of helicopters, including approximately 900 hours on the Bell 206. He had completed 20 hours on this helicopter in the 30 days immediately prior to the accident. The pilot had a valid night visual flight rules (night-VFR) rating and 51 hours night-VFR experience. However, he had accumulated only 5.5 hours instrument flying time and he did not have an instrument rating. The pilot commenced night marine pilot transfer training about 2 months prior to the accident, and had received 21 hours of night-VFR training that included more than 63 landings on ships at night. About half of these landings were to brightly lit decks. About 70 per cent of the landings had been conducted under dark-night conditions but his training did not include practice emergencies or distractions during night departures. He began carrying passengers less than 1 month prior to the accident.

The pilot had been working alternate days for 8 days prior to the accident. The longest shifts had been two of 8 hours duty time each.

Human performance levels vary through physiological cycles of approximately 24 hours. These are referred to as circadian rhythms. The most significant circadian low-point occurs between approximately 0200 and 0600. The effects of circadian dysrhythmia include poor judgement, increased reaction times, mental haziness or lethargy and a general decrement in psychomotor performance. On the day of the accident, the pilot had been awakened by a call from work at 0400 to pick up two marine pilots for a departure 1 hour later.

A constraint in human performance when operating at night is the eye's poor ability to quickly adjust from brightly lit areas, such as a ship's deck, to dark environments, such as over water. The human eye generally achieves a large amount of dark adaptation after 15 minutes with full adaptation occurring after about 40 minutes.

The Civil Aviation Regulations (CARs) permitted the operation of aircraft under night-VFR with certain provisions. Although the CARs restricted single-engine aircraft charter operations, the Civil Aviation Orders (CAOs) provided exemptions to these limitations for marine pilot operations. CAOs also required that operations that were conducted during visual meteorological conditions at night, do so in accordance with the helicopter's flight manual. Although the regulations and orders did not require a visual horizon when flying at night, there was no on-going requirement for a pilot to demonstrate an ability to fly an aircraft with sole reference to the aircraft's flight instruments.

The company operations manual required night-VFR flights to be flown such that flight attitude could be maintained by reference to external objects adequately illuminated by ground or celestial lighting. The helicopter's flight manual required that the pilot maintain orientation through visual reference to ground objects solely as a result of lights on the ground or adequate celestial illumination. Neither publication provided guidance or caution on the human factor limitations associated with night visual flying.

ANALYSIS

The pilot had a visual horizon during the transit to the ship and the lights of the town of Dampier would have provided a horizon to the south-east for the return transit. The ambient and ground lighting conditions would probably have been sufficient to meet the requirements of the company operations manual and the helicopter's flight manual, although it is unlikely that such conditions existed during the departure from the ship. The moon had set 13 minutes prior to the helicopter's arrival at the ship. The transit time to the ship would probably have been sufficient for the pilot to attain a large proportion of his visual dark adaptation and therefore he may have ascertained that there was an adequate horizon to the north-east. However, after landing on the ship, the pilot's dark adaptation would have been substantially destroyed by the ship's lights illuminating the deck area. Although the company operations manual and helicopter's flight manual required sufficient lighting to maintain flight attitude, neither publication provided guidance or caution on the human factor limitations associated with dark adaptation. Consequently, although the pilot thought he had an adequate horizon on which to maintain the helicopter's flight attitude, he had no objective measure with which he could ascertain the suitability of the conditions for continued flight in accordance with the company manuals.

The departure from the ship was unlikely to have been made with any discernible horizon because the moon had set 22 minutes before, the high overcast had obscured much of the celestial lighting and the pilot could not have achieved any dark adaptation in the brief period from the take-off to water impact. Deprived of an adequate external visual horizon, the pilot would have been unable to maintain the helicopter's attitude and departure profile without referring to the helicopter's flight instruments. Given his minimal instrument flying experience, the pilot may have had difficulty transitioning from visual reference to instruments during the departure. When the pilot became concerned at the "feel" of the tail rotor pedals, he diverted his attention from the helicopter's attitude and performance indications for an extended period. While the pilot was not monitoring the helicopter's flight attitude or performance, it is likely that the helicopter's collective control fell and the helicopter descended. Having been awakened at 0400, the pilot was working within the most pronounced low point of his circadian cycle which may have also adversley affected his ability to maintain his situational awareness during the distraction. His relative inexperience at conducting night marine transfers associated with possible circadian dysrhythmia may have reduced his situational awareness because he was unaware that the helicopter was descending until it struck the water.

SAFETY ACTION

The Bureau of Air Safety Investigation is currently investigating a perceived safety deficiency that has been identified as a result of this occurrence. The deficiency relates to:

- human factors involved with operating helicopters over water at night;

- passenger safety provisions for over-water helicopter operations; and

- the adequacy of current night-VFR requirements for over-water helicopter operations.

Any recommendation issued as a result of this investigation will be published in the Bureau's Quarterly Safety Deficiency Report.

Local safety action

The operator has increased the training requirements for pilots operating to ships under night VFR. These requirements include night training under moonless conditions and total cloud coverage, the introduction of basic instrument flying proficiency checking and the introduction of annual written human factors examinations.

The pilot of a Cessna 310 aircraft reported to Flight Service, after departing from Nyngan, that the right main landing gear appeared to have failed and he was diverting to Dubbo. He requested that emergency services be available for his arrival. An Alert phase was declared, and emergency services were placed on standby. The aircraft subsequently landed at Dubbo, but the right main landing gear collapsed during the landing roll.

The pilot later reported that he heard a loud bang from the right side as the landing gear was retracting, but the retraction cycle ended with normal cockpit indications. Later, during cruise, the airspeed was observed to be about 15 kts lower than normal. At Dubbo, as the landing gear was extended, the right main gear light failed to illuminate, and the gear unsafe light remained on. A low pass was flown and ground observers reported that the landing gear appeared to be down. The initial touchdown was made on the left main wheel, but as the aircraft settled onto the right main wheel the right main landing gear leg collapsed.

A subsequent inspection revealed that the right main landing gear strut had failed from fatigue cracking. The aircraft is heavily utilised in bank run activities, resulting in a high number of landing gear cycles.

The pilot of the Cessna 182RG was conducting flying training under supervision. Whilst carrying out a glide approach the airspeed decayed below that required to execute a normal landing. A missed approach was initiated, however, the aircraft contacted the runway heavily before becoming airborne. It was subsequently found that the rudder trim was jammed, and a PAN call was broadcast.

The aircraft was subsequently landed safely. The maintenance investigation revealed substantial damage to the landing gear and associated structure, as a result of the heavy initial impact on the runway. The reason for the jammed rudder trim has not yet been determined, however, it is considered to be as a result of the heavy landing.

The pilot of a Gippsland Aeronautics GA 200 agricultural aircraft was conducting topdressing of paddocks and was operating from a nearby forestry airstrip. The pilot had completed the first load with a reduced hopper capacity to assess the aircraft's performance. He determined that sufficient margin existed to increase the next load, and an additional 150 - 200 kg of superphosphate was added to the hopper for the second flight.

The pilot reports that the initial take-off roll appeared satisfactory, with the aircraft accelerating normally. However, shortly after lift-off, the engine coughed momentarily and the aircraft began to lose climb performance. The engine quickly recovered, but not before the climb gradient had been substantially reduced. The pilot had commenced dumping the load but was unable to clear the pine trees upwind of the agricultural strip.

The aircraft entered the trees wings level in the climbing attitude. The aircraft came to rest in an inverted attitude and was substantially damaged during the impact sequence. The cockpit structure survived the impact and the pilot was able to vacate the aircraft without assistance. Subsequent investigation by the aircraft operator did not establish a reason for the reported engine malfunction.

During the landing roll, the nose-wheel steering failed and braking efficiency reduced. After shutdown, the pilot observed hydraulic fluid coming from the front relief vent associated with the brake anti-skid system. A permit to fly was obtained from the Civil Aviation Safety Authority and the aircraft was ferried to Perth with the landing gear down and locked. After landing, the aircraft was towed to the operator's facilities due to inadequate steering and braking capability. Maintenance investigation by the operator traced the problem to internal leakage of hydraulic pressure through the anti-skid control valve to the low-pressure side of the brake system and then overboard. The problem was inherent with the anti-kid-equipped aircraft and the operator was pursuing suitable rectification action with the manufacturer.

Interim remedial action has been the introduction of a standard operating procedure to depressurise the hydraulic system after engine shutdown when parking the aircraft. Since the introduction of this procedure, there have been no further incidents.

Safety Action Statement

As a result of this occurrence, the Bureau of Air Safety Investigation is currently analysing a possible safety deficiency. The deficiency identified involves aircraft fitted with anti-skid braking systems. This static internal leakage may result in the loss of hydraulic system contents and subsequent loss of all hydraulic services.

Any recommendation issued as a result of this analysis will be published in the Bureau's Quarterly Safety Deficiency Report.

The pilot advised Sydney Flight Service, that on departure from Parkes, his aircraft had experienced a hydraulic failure, which resulted in landing gear retraction problems. The pilot then requested a diversion to Sydney instead of his intended destination of Bathurst, advising that the landing gear would be lowered using the alternate system. The aircraft subsequently made a normal approach into Sydney for an uneventful landing.

Investigation by company maintenance personnel could not fault the landing gear system, and put the problem down to air in the system. This aircraft was fitted with antiskid which is known to cause problems with hydraulic fluid loss. The operator was informed of other operator experience in this regard.

Safety Action Statement

As a result of this occurrence, the Bureau of Air Safety Investigation is currently analysing a possible safety deficiency. The deficiency identified involves aircraft fitted with antiskid braking systems. This braking option suffers from static internal leakage, which may result in the loss of hydraulic system contents and subsequent loss of all hydraulic services.

Any recommendation issued as a result of this analysis will be published in the Bureau's Quarterly Safety Deficiency Report.

The pilot reported that the engine stopped in the cruise at about 600 ft. He entered autorotation and landed in low trees and scrub. The engine stopped because the crank shaft drive gear bolt failed due to hydrogen embrittlement. When the bolt failed drive to the accessories was lost. The manufacturer has verbally assured CASA that this was an isolated instance of a bolt failure.

The pilot reported difficulty in maintaining directional control of the aircraft during the later stages of the landing roll. The pilot indicated that the left main gear collapsed, the left wing contacted the ground, and the nose wheel collapsed. The aircraft slid a short distance before coming to a stop. The pilot and his passenger were uninjured.

Following the accident, the pilot observed that the right-hand main tyre was partially deflated. Although the tyre was normally inflated prior to departure, it was unclear if this contributed to the pilot's difficulty in maintaining control of the aircraft during the landing roll.

On descent through 8,000 feet, the engine of VH-DBX started running rough. The pilot carried out the emergency check list procedures and found no response to throttle so he shut the engine down. Melbourne Flight Service (FS) was then informed by the pilot of his intention to land short of Goulburn. Another aircraft in the vicinity, VH-RPO, was diverted by FS to render assistance. The pilot of DBX did not declare an emergency, however FS initiate a Distress Phase. On short final to the selected landing site at approximately 20 feet AGL, the aircraft contacted a power line, rolled to the left and impacted the ground in a nose down attitude. The aircraft was then vacated with nil injuries. The pilot of RPO informed FS that an ambulance was in attendance and the Distress Phase was cancelled.

A report has been requested for the engine strip and inspection.