Operators are well on their way to meeting an FAA mandate to inspect and—if needed—replace thrust-reverser inner walls on Rolls-Royce Trent 800 engines to prevent thermal damage that, in the worst cases, has led to two inflight diversions.
The mandate is based on Boeing recommendations that should finally resolve a long-standing issue. Boeing learned more than a decade ago that the composite thrust-reverser (T/R) walls, part of the reverser system supplied by Spirit AeroSystems, can degrade when exposed to prolonged high temperatures. Insulation blankets, recommended by Boeing early on, provide a thermal barrier between hot engine air and the wall structure. But if the blankets are not installed correctly or suffer undetected damage, hot air reaching the walls can cause delamination or, in extreme cases, cause pieces to break apart.
Boeing and Rolls-Royce have issued several service bulletins recommending inspections and upgrades, including installation of blankets. In 2013, Boeing decided to recommend full wall replacements as well and began to put together a plan. In June 2014, Boeing issued a service bulletin detailing the procedure. The FAA’s airworthiness directive (AD), published June 17, is based largely on that bulletin.
“We are issuing this AD to detect and correct a degraded T/R inner wall panel,” the FAA explains in the AD’s preamble. “A degraded T/R inner wall panel could lead to failure of the T/R and adjacent components and their consequent separation from the airplane, which could result in a rejected takeoff (RTO) and cause asymmetric thrust and consequent loss of control of the airplane during reverse thrust operation.”
The AD covers Boeing 777-200s and -300s with Trent 800 engines and requires records checks, repetitive inspections and, if necessary, full wall replacements. Deadlines for the fix vary based on airplane configuration and work accomplished. Installation of “serviceable reverser inner-wall halves,” which eliminate the need for repetitive checks, must be done by July 22, 2020.
The FAA estimates that 55 U.S.-registered aircraft are affected. Aviation Week’s Fleet Discovery database shows about 175 Trent-powered 777s in service worldwide.
A Boeing spokesman confirmed that about 70% of the aircraft covered by the AD are already compliant, as operators opted to voluntarily follow Boeing’s recommendations.
While most of the in-service issues have been minor, the problem has been linked to two notable incidents. In June 2010, a British Airways 777-200 lost parts of its right engine’s inner wall and engine nacelle on takeoff from Singapore Changi Airport. The aircraft was en route to London’s Heathrow Airport. The crew determined it was safe to continue but then diverted to Amsterdam Airport Schiphol because the problem led to higher fuel burn on the flight.
In December 2012, a Royal Brunei Airlines 777-200ER headed for Dubai turned back to Heathrow after pieces of the right engine’s wall broke apart. This caused a “loud rumbling noise” and triggered an exhaust-gas temperature warning, a U.K. Air Accidents Investigation Branch report found. The aircraft had Boeing-recommended insulation blankets installed, triggering concern that mitigation techniques needed refinement. Subsequent Boeing bulletins revised the recommended blanket-installation procedures.