The US Federal Aviation Administration has issued a mandatory airworthiness directive (AD) for US-registered Viking Air DHC-4 and DHC-4A Caribou aircraft. The action, first issued by Transport Canada in November, came after an Australian operator performing a heavy maintenance check on a DHC-4 discovered that both of the upper engine mount bracket assemblies for one engine were cracked, a problem that could result in the engine ripping itself from the aircraft. Inspections of 10 other aircraft in the same fleet exposed five more cracked brackets, according to the FAA.
Within 10 flight hours starting 23 January, the agency is requiring US operators to perform a one-time fluorescent penetrant inspection of the mounts, an inspection both Transport Canada and Viking Air have also required or suggested.
Viking purchased the type certificate for the DHC-4 and six other De Havilland aircraft from Bombardier in February 2006.
In the USA, the AD is in large part directed at Pen Turbo Aviation, the Cape May, New Jersey-based operation that owns 37 of the 47 US-registered Caribou -nearly 80% of the fleet.
Pen Turbo Aviation president R Gobalian says a cursory check of his DHC-4 and DHC-4As has not turned up signs of the problem, although he has not yet performed the FAA-mandated test.
Virtually all of Pen Turbo's Caribou are parked at Cape May Airport in New Jersey awaiting engine make-overs and buyers. The company has a supplemental type certificate to convert the Pratt & Whitney R2000 radial-powered twins to Pratt & Whitney Canada PT6A-67T turboprops.
Gobalian's idea was to sell the conversion to the Australian Air Force, which uses more than a dozen R2000-powered Caribou. Despite the advantages - Gobalian says the $4 million-plus retrofit boosts payload and performance while greatly increasing engine life and reliability - the Australians have not placed an order.
Pen Turbo has completed the conversion of one aircraft and says a second will be under way once a sale is made.
Gobalian tells Flight International that interest in the aircraft is high in countries with little airport infrastructure, including Indonesia, Mozambique and New Guinea. Financing has been the key issue with long distance sales, however. "Who's going to repossess an aircraft on the other side of the world? If it leaves here, it's got to be paid for," he says.
Source: Flight International
