Operators of General Electric CF6-50 engines are expected to be given new options to meet a forthcoming US Federal Aviation Administration airworthiness directive (AD) which will call for corrective actions to the engine's low pressure turbine (LPT) nozzle locks.
The value of General Electric stock fell nearly 9% in a few hours earlier this month amid news reports about problems with the engine, which powers nearly 2,000 airliners worldwide.
The AD, which has been expected since a string of uncontained failures struck Continental Airlines-operated DC-10s last year, is due within 60 days. The turbine break-ups were traced to failures of the second stage LPT nozzle lock studs which were forced through the casing by the gas exhaust.
The first draft AD called for the replacement of the original lock mechanism with nozzle locks based on the design of the -80C2. This, however, requires a full LPT teardown and the AD is now expected to also include at least two new options to provide operators with an interim solution that will provide several years' worth of operational compliance without the need to remove the engine.
The options include replacing the locks with new ones of the original design. GE points out that the problems are caused by a "time and temperature" phenomenon, and should not therefore recur before the redesigned locks are fitted as a long term solution. The other shorter term option is for operators to drill holes into the LPT case and insert bolts through the holes.
In an apparently unrelated event, the US National Transportation Safety Board has recommended the FAA issue emergency ADs covering the inspection of high pressure turbine (HPT) stage one discs. This follows the uncontained failure of a CF6 engine on a US Airways Boeing 767 in September. The recommendation calls for immediate disc inspections of recently maintained HPT modules, and for operators to review maintenance procedures.
Source: Flight International
