Guy Norris/LOS ANGELES Paul Lewis/WASHINGTON DC
General Electric has begun removing the first of 90 GE90 engines from the worldwide Boeing 777-200 fleet after turbine blade separations caused two in-flight shutdowns and one turnback.
The problems, all of which afflicted 777-200ERs operated by Saudi Arabian Airlines, were caused by "reverse bending" of the second stage high pressure turbine blades, leading to cracking and structural failure.
The bending was caused by movement of the dampers either side of the base of the blade, which set up vibratory stress in the engine. The problems had been spotted in late 1998 and a redesigned blade and damper combination, with "anti-rotational" tabs, was introduced on to the GE90 production line from November 1998.
All the failures occurred on pre-modified engines with 1,400 cycles or more, during June, July and November last year. Following the third incident, GE opted to begin an immediate programme to replace 68 dampers and blades in the turbine section of all 90 engines with 1,200 cycles thought to be at risk from the defect. "We chartered an aircraft full of engineers and spares, plus an Antonov An-124 with a spare engine, and sent them to Saudi Arabia," says GE which adds that "the whole goal is to have no aircraft stranded on the ground because of this".
The company believes the difficult task is within its reach because of the "huge infrastructure of modification and overhaul sites we have available".
GE plans to have either removed, or be in the process of replacing, the first 30 powerplants by 15 January. The bulk of these are operated by Saudi Arabian, with the remainder mainly powering aircraft flown by Aeroflot and Air France.
The remaining 60 engines are due to be modified during normal or accelerated maintenance.
Source: Flight International
