CFM International has sent an alert to Boeing 737 operators recommending ultrasonic inspections within the next 20 days to fan blades on CFM56-7B engines with more than 30,000 cycles since they were delivered.

The service bulletin released on 20 April also calls on operators to perform inspections on fan blades with more than 20,000 cycles by August and on all fan blades as soon as they reach 20,000 cycles.

About 680 engines are covered under the 30,000-cycle inspection deadline and 2,500 engines fall under the August deadline, says CFM, a joint company formed by GE Aviation and Safran.

The inspections target the oldest engines in the global fleet of CFM56-7B engines, which has accumulated 350 million flight hours since entering service 21 years ago, CFM says.

The inspection should then be repeated for all engines with more than 20,000 cycles on intervals of 3,000 cycles, representing about two years of average airline service, says CFM.

The service bulletin comes three days after a fan blade blew out of a CFM56-7B engine with 40,000 cycles on a Boeing 737-700 operated by Southwest Airlines. Pieces of the engine or cowling penetrated the wing and fuselage, blowing out a window and killing one passenger.

A quick inspection of the damage by the US National Transportation Safety Board found signs of metal fatigue where blade fractured at the hub. That early finding echoed the NTSB’s preliminary report on a similar blade-out failure of the same engine in August 2016, which also led to engine shrapnel puncturing the fuselage and wing of a Southwest 737-700.

CFM’s newly-released service bulletin stops short of a mandatory inspection, but airlines, such as Southwest and United, have already moved to scrutinise metallic fan blades on older CFM56-7Bs.

The US Federal Aviation Administration announced on 19 April that a directive with a mandatory fan blade inspection procedure will be released within two weeks. The FAA’s airworthiness directives are often patterned on related service bulletins issued by manufacturers.

Source: Cirium Dashboard