Qantas has replaced all the fan blades it considered to be "at risk" on Rolls-Royce RB211-524G/H engines following inspections after a fan blade failure on a British Airways Boeing 747-400 last month between Sydney and Bangkok. The Australian Transport Safety Bureau (ATSB) report reveals that a bonding failure in the manufacturing process was at fault.
The ATSB says the crew experienced vibrations and received an "ENG 3 reverser" warning on the engine indicating and crew alerting system (EICAS). "An initial engineering examination revealed an engine fan blade had failed, and that debris had punctured the engine cowl, the right wing leading- and trailing-edge flaps and the fuselage, damaging a structural member above the wing-root area," says the ATSB. The inspection found fractured fasteners and other components beneath the fan cowls, and damage to the structure associated with the thrust-reverser assembly. Debris from the No 3 engine fan was also found embedded within the nose cowl of the No 4 engine.
"The failed fan blade had fractured immediately above the dove-tail root block, beneath the annulus filler position. The fracture surface showed features typical of a progressive fatigue cracking mechanism, with the crack origin located adjacent to the blade centreline, approximately 50mm [2in] back from the leading edge," says the ATSB, which attributed the fracture to a "lack-of-bond" defect that had "developed during the blade manufacturing process".
The failed blade had accumulated 9,444 cycles since new and 1,299 cycles since last re-work.
Rolls-Royce issued an alert service bulletin on 12 March, calling for "management [removal from service] of blades considered to be at risk of cracking from bonded areas". Affected engines are fitted to some 747s and 767s.
Source: Flight International
