The long-delayed flight tests of the Pratt & Whitney PW4098-powered Boeing 777-300 are not expected to resume until at least the end of this month following an incident at SeaTac International Airport, near Seattle, in which a new engine slipped in its handling cradle.

P&W says that the PW4098, which was being delivered to Boeing after being fitted with newly redesigned compressor stators, "-dropped within the confines of its shipping cradle" after unloading.

P&W, Boeing and the US Federal Aviation Administration are inspecting the engine for damage. The probe is focused on the bearing compartment and fan case. Despite reports of some harm to the fan track lining, P&W says: "We think the engine is fine and will be able to return to flight status."

Nevertheless, the incident has pushed back the start of flight tests. These were due to restart around 21 July after a delay of almost four months after cracked compressor stators were discovered in the single PW4098 mounted on one side of the 777-300 test aircraft, WB551.

The first part of the flight tests involved one PW4090 on one wing and a 436kN (98,000lb)-thrust PW4098 on the other. Despite the incident, 777 test and validation chief engineer Roger Houck says: "We think we're in pretty good shape to get flight tests restarted at the end of July."

The engine was originally due to be cleared for 777-300 operations in late June, with first deliveries to Korean Air Lines expected to begin in October. First deliveries are now scheduled for December.

The FAA has issued an airworthiness directive ordering the inspection of General Electric GE90 engines for cracks in the high-pressure compressor (HPC). The FAA says 10 HPC spools have been found with cracks. "The HPC stage 2-6 spool may develop cracks in the stage 3-4 and 4-5 interstage seal teeth that could propagate into the stage 3-4 and stage 4-5 spacer arms, aft of the seal teeth," it adds.

The FAA itself has determined that the most likely cause of the cracks, which it says could cause an uncontained failure if not corrected, is the formation of zones of excessive heat. These are produced when the rotating seal teeth rub into the static honeycomb material, says the agency.

Source: Flight International