Pratt & Whitney is retrofitting all PW4164 and PW4168 turbofans powering the Airbus A330 with a redesigned blade platform after tests revealed the potential for high N1 (low-pressure-spool rpm) rotor imbalance and the loss of the fan-containment system in the event of a fan blade detaching - a risk with the original platform design.

In the interim, the US Federal Aviation Administration has issued an airworthiness directive (AD) calling for the inspection of fan blades for cracks, a one-time ultrasonic inspection of the fan-blade root attachment, another one-time inspection of the root-attachment dimensions and repetitive lubrication of the fan-blade part-span shrouds (or clappers). The replacement of the fan-platform with the redesigned assembly is the closing action for the AD, which becomes effective on 11 June.

"During some post-certification test runs, we liberated a blade intentionally, and analysis of the data indicated that we could have a problem. We and the FAA consider it low risk, but we are taking immediate action in view of the extended-range twin [engine]-operations considerations," says P&W. When the blade was released during the test, it caused "-more damage than was expected". The FAA says that the test resulted in the "liberation of the fan-containment system, causing loss of structural support of the engine-inlet cowl."

Source: Flight International