Regulations governing helicopter windscreen strength are inadequate and at least partially responsible for a Petroleum Helicopters crash in Louisiana in 2009 that killed eight, says the US National Transportation Safety Board.
In its final report on the crash of a twin-engined Sikorsky S-76C++ that struck a female red-tailed hawk at 135kt (250km/h) and 850ft (260m) altitude in overland cruise flight to an offshore oil rig, the safety board says the "lack of requirements for birdstrike-resistant windshields contributed to the crash". It calls on the Federal Aviation Administration to issue more stringent requirements. Both pilots and six of the seven passengers were killed in the accident.
Investigators say a loud bang was heard on the cockpit voice recorder, followed by sounds consistent with rushing wind and a power reduction on both engines. The cause of the power reduction was likely to have been the fire extinguisher T-handles, which came out of their detents and pushed both engine control levers into or near the flight idle position.
"The pilots were probably disoriented from the broken windshield and rushing air and were unable to react in time to maintain control of the helicopter," says the NTSB.
The helicopter was originally equipped with laminated glass windshields that complied with European bird-strike resistance standards. Petroleum Helicopters replaced the windshields with lighter-weight, aftermarket cast acrylic windshields built by Bell Helicopter affiliate Aeronautical Accessories that were not required to meet birdstrike resistance standards.
Sikorsky after the crash alerted operators that the aftermarket screens were less tolerant to impact damage than the heavier original equipment glass.
Contributing to the accident, the board said, were the lack of FAA regulations and guidance requiring helicopter windshields to be resistant to birdstrikes, the lack of protections that would prevent the T-handles from inadvertently dislodging out of their detents, and the lack of a master warning light and audible system to alert the flightcrew of a low-rotor speed condition.
Source: Flight International
