The FAA, in its latest step to end a 25-year run of General Electric CF6-80C2 in-service fire risks tied to fuel manifolds, proposes adding repetitive inspections and parts replacements to an existing list of mandates.

The proposed rule, published Friday [LINK: https://www.federalregister.gov/articles/2014/01/17/2014-00833/airworthiness-directives-general-electric-company-turbofan-engines], would require operators to replace loop clamps at designated intervals that vary based on several factors.

The rule would also add inspections for clamps and fuel manifold feeder tubes, and mandate removing certain drainless manifolds from service. It also attempts to clarify and simplify requirements from three previous airworthiness directives (AD), dating back to 1990, that cover additional inspections and parts swaps.

ADs issued in December 1990 and November 1991 ordered replacement of specific manifolds. A March 2009 order requires inspections of certain drainless manifolds and replacing associated clamps.

“We are superseding these ADs to eliminate potentially confusing and contradictory requirements” as well as to address additional risks, FAA says in the draft directive. The FAA says the directive will cover 1,126 engines on U.S.-registered aircraft. Estimated compliance costs are about $35,000 per engine.

Since the 2009 directive, at least six in-service fuel leaks have been reported on the engine type—five on CF6-80C2s and one involving a CF6-80E1, FAA says. The most serious incident was the Feb. 25, 2013, CF6-80C2 engine fire onboard a China Airlines Boeing 747-400F shortly after it arrived at Dallas/Fort Worth International Airport (Aviation Daily, Nov. 13, 2013). A probe traced the leak to a fractured feeder tube beneath the No. 2 engine fuel shroud.

That incident was the fourth undercowl fire linked to drainless shrouds, which GE introduced in 1996.

Investigators determined that the China Airlines aircraft engine’s manifold configuration was not covered by FAA’s 2009 directive, but inspections added to the CF6 maintenance manuals by GE and applicable to the China Airlines engine called for the same checks.

The China Airlines engine was in compliance with all directives and service bulletins (SB), except for one, investigators found. That SB, No. 73-0371, was issued just days before the engine involved in the China Airlines incident left its last scheduled shop visit, and the SB’s recommended work was not part of the work package.

The bulletin introduced a new fuel manifold configuration and orientation designed “to prevent fuel manifold fractures and wear through the [feeder tube] . . . that had resulted in previous fuel leaks and undercowl fires,” NTSB explains in its report on the China Airlines incident.

FAA’s proposed directive does not reference SB 73-0371.