JUSTIN WASTNAGE / LONDON
Petroleum Helicopters lifts stand-down, while NTSB probes engine-related crash
US offshore helicopter operator Petroleum Helicopters (PHI) has begun re-introducing Bell 407 single-turbine helicopters following an engine-related precautionary stand-down in mid-December.
PHI suspended operation of its Model 407s following a 2 December fatal crash about 95km (50nm) south of Sabine, Texas, when the helicopter was returning from a Gulf of Mexico oil field.
Air Logistics is believed to have had a similar engine incident on the ground. Bell Helicopter issued an information letter in mid-December stating that preliminary investigation by the National Transportation Safety Board (NTSB) "suggests the incidents may be engine-related".
Rolls-Royce, whose Allison 250-C47B powers the helicopter, says it is assisting Bell in the NTSB investigation. PHI started returning its 407s to flight in late December after completing inspections recommended by Bell, and the manufacturer says there is not "an immediate need to take further action". There are 548 Model 407s in operation across 41 countries, the company says.
The NTSB investigation taking place in Indianapolis, Indianais focusing on the 250-C47B for the 407 rather than the -C47M used on the MD Helicopters 600N,due to differences in the engine running speed.
An earlier Bell information letter says the cause of the first incident was the fourth-stage turbine wheel, which was found to have an over-blended, thin trailing edge. The blade was blended beyond standard requirements, and Bell recommended a one-time inspection to verify the trailing-edge width. Turbine wheels with over 1,000h must be inspected within the next 150h, while those with less than 1,000h need inspection every 300h.
PH says it is returning aircraft to flight as it completes checks on its fleet of more than 30 aircraft. The Bell 407 helicopter fleet has exceeded 1 million flight hours. The milestone comes less than eight years since the light single-turbine machine entered service. More than half the total number of hours has been flown in the past three years, says Bell.
Source: Flight International
