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CFM Tackles Drive Shaft Bearing Issue On LEAP-1B Engine

CFM International is redesigning the bearing in the radial drive shaft of the LEAP-1B engine.

LOS ANGELES—CFM International said it is redesigning the bearing in the radial drive shaft of the LEAP-1B—which powers the Boeing 737 MAX—after five incidents in which an engine was shut down inflight following activation of the oil filter bypass light indication in the cockpit.

The action comes as EASA issued an airworthiness directive (AD) mandating recurring inspections of the transfer gearbox modules (TGB) 1 and TGB2 scavenge screens, which indicate if any metallic particles are in the oil system. The EASA AD, which only affects European-registered aircraft, is expected to be adopted worldwide and follows a service bulletin issued by the General Electric and Safran Aircraft Engines joint venture on Feb 1.

The radial drive shaft is part of the accessory drive train (ADT) which was developed for the LEAP by Safran Transmission Systems. The ADT, which takes power from the engine to drive other systems on the aircraft, also includes the accessory gearbox and the transfer gearboxes.

Airlines have been inspecting engines for the issue since before the MAX fleet was grounded in mid-March. “Late last year we had several events where in the cockpit crews noticed a delta pressure across the oil filters causing them to shut the engines down,” CFM EVP Allen Paxson said. “We later found out we were generating particles from the radial drive shaft on a group of engines, so we quickly put an inspection on the screen itself.”

The particles are visible “well before we can detect them with the system, so it’s an early warning to make sure we don’t have any more of these events,” Paxson said, adding the inspection is simple to perform and takes 15 minutes. So far less than 10 other engines have exhibited similar symptoms of the distress which Paxson adds is limited to the -1B and does not affect the LEAP-1A powering the AirbusA320neo family.

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