One passenger was fatally injured when a helicopter crashed in bad weather near Cairns last year.
At 1130 on 12 March 1999 the Bell 206L-3 helicopter departed from Green Island on a routine passenger charter flight to Cairns airport. The helicopter took off in light drizzle and the pilot elected to track back to The Pier via the shipping channel.
The Bureau of Meteorology had issued an amended aerodrome forecast for Cairns at 0808 for the 24-hour period from 1000. It forecast an easterly wind at 15 knots, visibility of 9,000 metres and light rain. Some cloud patches were expected with a base of 800 feet a broken layer at 1,800 feet and overcast at 10,000 feet. Periods of up to one hour of heavy rain, scattered cloud at 800 feet and broken cloud at 1,500 feet were expected over the forecast period.
At 1139 the helicopter was cleared by Cairns Air Traffic Control to track to The Pier, not above 500 feet. The controller advised the pilot that within seven to nine kilometres from The Pier the cloud base was between 800 and 1,000 feet with some showers and visibility less than 10 kilometres.
As the helicopter continued along the shipping channel, the pilot noticed that the weather ahead was deteriorating. A short time later, he descended the helicopter to about 150 feet to keep the water surface in sight, and reduced speed.
The weather conditions continued to deteriorate, and eventually the pilot flew the helicopter at 50 feet or less above the water in light to moderate rain. By this time he could no longer see any channel beacons.
The pilot turned on the windscreen demister as condensation had begun to form on the inside and he also armed the inflatable floats, which were fitted to the skid-type landing gear.
At about 1146 the pilot asked the controller for directions to The Pier. He was advised that The Pier was on a bearing of 205 degrees M, at a range of three kilometres (about 1.5 nautical miles). At about that time, visibility had deteriorated to the extent the pilot could not determine where the helicopter was.
Then, noticing that the helicopter had climbed to 100 feet altitude, the pilot placed it in a gentle descent to try and sight the water again. A short time later the helicopter contacted the water and rolled inverted.
The pilot and five passengers escaped from the fuselage but one passenger was trapped inside the cabin and did not survive. One passenger sustained serious injuries, four experienced minor injuries and the pilot was uninjured.
Actual weather conditions
The air traffic controllers on duty in the tower said that the weather had been fluctuating significantly and rapidly throughout the morning. There were periods when the weather conditions met the criteria for VFR (Visual Flight Rules) flight and intervals of low cloud and very heavy rain, some of the worst conditions controllers said they had seen at Cairns airport.
Radar images and rainfall rates suggested that the visibility in the area of the accident would have been reduced to a few hundred metres or less. Personnel who were at The Pier at the time of the accident described the rainfall as torrential with visibility as low as one car length.
The weather information passed by the controller to the pilot was based on his visual assessment of the weather in Cairns Harbour as he saw it from the air traffic control tower.
Height speed and track
Air Traffic Services radar data confirmed that the helicopter was initially tracking via the Cairns Harbour shipping channel at about 100 knots and at an altitude of 200 feet above mean sea level.
At about seven kilometres from The Pier the speed gradually decreased to between 55 and 60 knots and then to below 40 knots. The last recorded speed was 31 knots. The altitude recorded during the last two minutes of the recording was 100 feet with one reading of 200 feet.
The pilot reported that during an earlier flight to The Pier the airspeed indicator was not functioning normally and did not indicate above 40 knots. He thought that the fault was probably due to water in the pitot-static system and expected it to clear during the flight to Green Island. However, the fault remained.
The airspeed indicator did not function during the flight when the accident occurred. The pilot said he relied on the ground speed display on the GPS (Global Positioning System) unit. The ATSB's occurrence brief stated that the GPS receiver records ground speed and not indicated airspeed.
Examination of the wreckage confirmed that the helicopter had struck the water in a slight left skid-low nose attitude, and at low forward and vertical speeds.
Circumstances and issues
A number of issues were highlighted as possible contributing factors to this accident.
There was an expectation from the helicopter company that the pilots would 'give it a go' if weather looked doubtful; to 'have a look before turning back.' However, there was no pressure to complete flights in unsuitable weather conditions.
The pilot held an ATPL (airline transport) licence with a total of 5,321 hours and 1,656.1 on the Bell 206L. His decision to track via the channel was based on his experience with mechanical turbulence on the alternative route, which was coastal via False Cape. The alternative route had proven uncomfortable for passengers in the lee of high terrain on the southern side of Trinity Inlet when the wind was a south or south easterly greater that 15 knots.
The pilot followed his usual practice during conditions of deteriorating visibility of descending to keep sight of the water and reduced airspeed. Although the visibility was poor he continued with the flight because of his experience in similar conditions and the information from the controller which suggested that the weather would improve as he approached Cairns.
The pilot's night VFR rating was not current and he disliked instrument flying since getting the rating in 1992. In any event, the helicopter was not Instrument Flight Rules (IFR) rated. In the prevailing conditions the pilot did not consider that turning at low altitude and flying back to better conditions was a safe option.
The pilot reported that the visibility during the return flight from Green Island was the worst that he had ever experienced. The sea surface had become completely flat and featureless and had blended entirely with the rain. By that time it was too late to turn around.
He reflected that it might have been better to track coastal because the vegetation and other land features would have provided a higher level of visual contrast against the rain and cloud and may have enabled him to complete the flight safely. He would have been able to land the helicopter and await passage of the weather.
The formal analysis of this accident noted the following circumstance as valid contributors:
- The pilot continued the flight into adverse weather beyond the point of having a visual external reference.
- The risk of not being able to turn around onto a reciprocal track without visual clues was high as the pilot was not instrument rated and the helicopter was not IFR rated.
- The pilot's operating culture was conditioned from having 'got through' adverse weather on previous occasions.
- Having decided to track via the shipping channel because of turbulence consideration on the coastal route, the pilot overlooked the coastal route as an alternate course of action.
- The weather information passed by the tower controller probably placed an expectation in the pilot's mind that he could negotiate the weather successfully. *
- More details of this accident are contained in Occurrence Brief 199901009.
|Type:||Educational Fact Sheet|
|Publication date:||11 June 2001|