Operators of the Sikorsky S-92 already struggling with availability challenges due to spare parts shortages could be facing a fresh headache after US regulators mandated urgent inspections of the GE Aerospace CT7 engines that power the heavy-twin.

Detailing the requirement in an emergency airworthiness directive issued on 28 February, the Federal Aviation Administration (FAA) says the action has been prompted by “at least four reports of failures” of a component vital to the monitoring of engine operating parameters.

S-92 Generic-c-Sikorsky

Source: Sikorsky

S-92 operators have already been dealing with spare parts shortages

Although failure of the part itself – the torque reference tube magnetic insert braze joint on the power turbine drive shaft assembly – does not endanger the aircraft, it could still pose a serious risk, the FAA says.

“This condition, if not addressed, could result in improper torque and engine speed indications, which in combination with specific phases of flight, could create an unacceptably high flightcrew workload in maintaining control of the aircraft, and result in consequent loss of control of the aircraft,” the directive states.

Under the directive, affected operators must, before further flight, carry out an ultrasonic inspection of each powerplant to check for “inadequate braze coverage”.

If the braze coverage is found to be less than 42%, the power turbine drive shaft assembly must be repaired or replaced.

The directive affects CT7-8A and -2E1 engines, powering the S-92 and Leonardo Helicopters AW189, plus the T700-series turboshafts which equip some former military-operated Sikorsky UH-60 Black Hawks now on the civil register.

It applies to engines equipped with certain power turbine drive shaft assemblies which have less than 100h of operation since new or replacement of the torque reference tube.

There are no indications of how many aircraft are covered by the directive, although industry analysts believe around 30 S-92s are impacted.

GE is continuing to investigate the root cause of the problem and further regulatory action could be required, the FAA says.

Other variants of the CT7 engine which power the military AW101 and NH Industries NH90 are also included in the directive.

GE initially issued service bulletins relating to the problem on 26 February. The directive has also been adopted by the European regulator.