The intentional alteration of weight documents and performance charts by Carson Helicopters is among the probable causes of a fatal August 2008 crash of a Sikorsky S-61N helicopter that was being used by the US Forest Service for firefighter shuttling.
"Carson engaged in a bargain that violated the trust of their crew members, the firefighters that they carried on board, and the aviation industry," says US National Transportation Safety Board chairman Debbie Hersman. The NTSB also faulted the Forest Service and the Federal Aviation Administration for not properly overseeing Carson. "Public aircraft have been made the orphans of the aviation industry," Hersman added.
The twin-engine helicopter struck trees and terrain while attempting to take off from a location 6,000ft (1,830m) above sea level near Weaverville, California while transporting firefighters. Of the 13 passenger and crew on board, four survived with serious injuries.
Investigators found that the crew had been using emergency-only power performance data rather than the normal take off "five minute power" due to errors in the charts supplied by Carson. "This led the flight crew to develop their flight plan for more lifting capability than actually existed," says Sikorsky, in an analysis of the crash supplied to the NTSB. The analysis shows that the difference in lift was approximately 545-568kg (1,200-1,250lb) for the conditions at the time of the crash.
Investigators also found that the accident helicopter was 652kg overweight, in part due to Carson's incorrect reporting of the S-61N weight to the Forest Service.
Along with the flightcrew's failure to address "issues related to operating the helicopter at its maximum performance capability", contributing factors include lack of crash-resistant fuel tanks, separation of the non crash-resistant seats from the floor, and the use of an "inappropriate mechanism" on the cabin seat restraints.
Carson blames one of its managers "who acted without the knowledge or consent" of senior management for the performance chart and weight estimate errors, but maintains the crash was caused by a loss of power in the number two engine. "Extensive independent real-world flight testing has confirmed that even at weights exceeding what the NTSB has attributed to the accident aircraft, N612AZ should have had enough power to fly away from [the pad] with two properly operating engines," the company says.
Source: Flight International
