Report inconclusive about why R44 ditched in water

 - January 31, 2007, 5:12 AM
The British Air Accidents Investigation Branch (AAIB) has issued its report on an accident last January. A British-registered Robinson R44 (G-NUDE), ditched and sank on an attempted flight between Cabo de Hornos, Chile, and Teniente Marsh Airbase on King George Island, Antarctica. The two occupants were rescued after 10 hours in seas of 35 degrees F.

According to the AAIB bulletin the two pilots had waited several days for a strong enough tailwind for the 440-nm crossing before departing at 2105 GMT on January 27 last year. At 700 feet, the 30-knot tailwind gave them a groundspeed of 120 knots. They made position reports to the Chilean Coast Guard at 30-minute intervals using a satellite phone. Four hours after departure they were approaching King George Island, but saw sea fog ahead and turned to the southwest, hoping to make landfall.

Soon after this they felt a vibration that appeared to come from the engine area, followed soon after by a drop in power. A slow descent was required to maintain rotor RPM. Some 30 seconds later, after losing about 200 feet, the oil pressure indication dropped to zero and the warning light came on, followed almost immediately by complete loss of engine power.

The pilot flying, who held a UK private certificate with 450 hours total time, 420 on type, entered autorotation while the more experienced left-seat pilot climbed out onto the skid and released the liferaft and emergency kit. At an estimated 20 feet above the surface he jumped into the water, but the raft’s self-inflation line became entangled with the skid, causing premature inflation and separation of the liferaft from the pilot and the helicopter. Fortunately, the pilot in the water was able to recover the raft before it blew away.

Meanwhile, the pilot flying turned the helicopter into the wind and touched down with no forward motion. As soon as the rotor blades stopped and the helicopter started to sink; he jumped into the sea and they both boarded the liferaft. They were both wearing immersion suits but had the hoods down to accommodate headsets. They did not have time to raise their hoods and water entered their suits through the unsealed neck openings.

They activated their emergency beacon but rescue was slow. Unable to contact Chile, they used their satphone to call their homes in England. One pilot could only reach his answering machine. The other managed to talk to his wife, who contacted the UK Coast Guard, which in turn alerted its counterpart in Chile. Most of the pilots’ time was occupied bailing water out of their liferaft, a routine they believe offset hypothermia. Although they could hear the sound of a Chilean Air Force Twin Otter overhead, it was six hours before a break in the fog opened and they were able to fire a flare. Four hours later they were rescued by a Chilean Navy ship.

According to the AAIB, the pilots were unwilling to be specific regarding the amount of fuel on board, but they claimed it was sufficient for the flight. An unmodified R44 with an auxiliary fuel tank carries 48.8 U.S. gallons, which would have provided endurance of just over three hours.

Before the flight, the helicopter was fitted with a new crankshaft idler gear bolt as required by FAA airworthiness directive 2002-23-06. Investigators discounted failure of the new bolt as the cause of the power loss because the helicopter had flown for 16 hours following the bolt change. Also, a failure of the bolt would have led to immediate engine stoppage, not the gradual loss of power experienced. However, investigators determined that weather conditions at the time held substantial risk for carburetor icing. The pilot flying said he was aware of the risk and used carburetor heat. Neither pilot considered that carburetor icing was a causal factor in the power loss at the time of the failure, and it has not been possible to recover the helicopter from the seabed for further examination.