GUY NORRIS / HARTFORD
Pratt & Whitney, Boeing and the US Air Force are working to improve the reliability of the F117-100 turbofan powering the C-17 airlifter following a rise in unscheduled removals and unsatisfactory durability in the wake of the Afghanistan and Iraq campaigns.
Almost 550 F117 engines, the military version of the PW2000 that powers the Boeing 757, have been delivered to Boeing for the C-17 production line, with 490 in operation. Since entering service in 1991, the F117 fleet has passed the 2 million engine flight hour milestone, but "they are taking a bit of a hit as far as time-on-wing performance is concerned", says P&W F117 programme director Steve Peery.
The rise in removals is linked to the increased tempo of operations in the harsh environments of Afghanistan and the Middle East, where blade, vane and sealing erosion is a severe problem, he adds.
"We are aiming for a 10-20% improvement, and we believe it is achievable," says Peery. Durability is being tackled through production and maintenance improvements, particularly through the use of an advanced diagnostic engine management system - jointly developed by Boeing and P&W. Using diagnostic data downloaded from the F117's full authority digital engine control units, P&W is increasing use of predictive maintenance techniques to offset the worst problems before they occur. P&W's average fleet time-on-wing target is between four and five years, although it admits this depends on where the C-17s are based and the type of operation.
The focus is now on improving air seals and clearance control systems to "counter performance erosion in austere conditions". Longer- term improvements being studied include improved erosion-resistant coatings for the high-pressure compressor and limiting use of the thrust-reverser in the landing roll-out. The F117 differs from the civil PW2000 in using core-thrust reversers, which can be deployed in flight for tactical descent and approaches.
To date, the USAF has ordered 180 C-17s and 800 F117 engines.
Source: Flight International
