The US Army is hoping to return about half its grounded fleet of 466 Boeing CH-47D/MH-47E Chinooks to flight status after being inspected for potentially fatal cracked transmission gears first discovered on an RAF machine during a depot-level overhaul.
A worldwide flight suspension order was issued as a result of cracks found in one of the planetary gears that make up the reduction gearbox. A subsequent inspection of Boeing's own inventory revealed another four defective components out of around 150 checked. "Preliminary indications are that the gear's spherical bearing raceway may not have been properly ground during the manufacture process. Improper grinding can produce surface cracks, leading to stress, fatigue and fracture potential," says the US Army.
Efforts focus on auditing the record-keeping of New York-based MFR, which grinds the gears, to accurately identify suspect production lots. The cracked gears have so far been traced to two separate batches. The US Army wants to restore to flying status 200 CH-47s equipped with gears supplied by a different manufacturer.
Source: Flight International
