The European Aviation Safety Agency (EASA) has mandated inspections and a reduced life limit for Airbus A320-family trimmable horizontal stabilizer actuators (THSAs) after tests by the manufacturer and supplier United Technologies Aerospace Systems (UTAS) revealed unexpected wear.

The EASA airworthiness directive (AD 2014-0011), issued Jan. 9, orders A318, A319, A320 and A321 operators to adopt Airbus-recommended service instructions issued last July. Among the tasks: inspect THSAs at 48,000 hours or 30,000 cycles or by May 23, 2013, whichever occurs later, and repetitive checks at prescribed intervals based on total estimated time in service.

The directive also requires any THSA with at least 67,500 flight hours to be modified in accordance with the Airbus service bulletin instructions before being returned to service.

UTAS notes in comments on EASA’s draft directive that the units are on-condition, meaning operators typically don’t track hours and cycles. Airbus issued a service letter with instructions on how to estimate in-serivce time.

UTAS also notes that its has delivered to Airbus test results that suggest a flight cycle limit will need to be applied.

“This document demonstrates fatigue limit also in term of flight cycles for the lower attachment point” not addressed in the Airbus service bulletin, UTAS explains, “as the flight cycles threshold has not been yet reached by the fleet.”

EASA says that Airbus is working to codify the flight-cycle limit, but adds that an update isn’t expected before 2015.

Aviation Week Intelligence Network’s Fleets database shows that the oldest A320s have just begun to surpass the revised flight-hour limit that renders THSAs in need of service. There are about 30 A320s with at least 70,000 flight hours, Fleets shows, with the fleet leaders being four Air Canada A320s with between 72,000 and 73,000 flight hours.

Each of the aircraft, which are among the first 85 A320s built, has about 31,500 cycles, Fleets shows.

While EASA’s requirements list a cycles interval that factors into determining the inspection schedule, the rulemaking documents don’t discuss the possible THSA cycles limit.