July 16, 2013
Credit: Dubai Airports
The European Aviation Safety Agency (EASA) is ordering swaps of high-cycle trimmable horizontal stabilizer actuators (THSAs) on Airbus A330s and older A340s after tests on a similar design fitted on A380s showed less-than-expected life limits.
Airbus in a July 11 All Operators Telex (AOT) says the problem is in the THSA’s no-back brake, which helps prevent uncommanded movements if the actuator malfunctions. Tests on an A380’s THSA revealed that the no-back brake’s carbon disks showed premature wear, causing the brake to lose efficiency.
The A380’s THSA is similar to those installed on all A330s as well as A340-200s and -300s, prompting EASA to act on the older Airbus widebodies first. The regulator says that each THSA must be replaced with a “serviceable unit” before 16,000 flight cycles. EASA is evaluating whether to reduce the life cycle limit even further, “probably” down to 12,000 cycles, the regulator says in the directive.
In the meantime, EASA set a replacement schedule for affected TSHAs with more than 16,000 cycles, capping total cycle times at about 24,000, depending on the unit’s service history and the aircraft model the unit is flying on. The schedule calls for all THSAs with at least 16,000 cycles to be removed from the fleet by February 2016.
EASA has not indicated if it will issue a similar order for A380s. The 10 A380s with the highest usage by cycles, all flown by Emirates Airline, had between 2,000 and 2,700 cycles as of April 30, according to Aviation Week Intelligence Network’s Fleets database.