Emergency AD mandates new engine inspections for stored 737s

[caption id="attachment_414296" align="alignright" width="550"] Idled Alaska Airlines 737s at Portland International Airport. Photo/PDX[/caption] An emergency airworthiness directive (AD) issued today by the Federal Aviation Administration ( FAA ) requires inspections of the engine bleed air fifth stage check valve on all 737 Classic and NG aircraft that have not been operated in flight for seven or more consecutive days, or have been operated for ten or fewer flight cycles since returning to service from storage. While in most cases these inspections involve a straightforward manual inspection of the components of the valve for signs of corrosion, faulty valves requiring replacement could cost operators tens of thousands of dollars per valve. Today’s emergency AD was prompted by four recent incidents of single-engine shutdowns found in 737s aircraft coming out of storage and follows a similar multi-operator message (MOM) dispatched by Boeing earlier this month alerting 737 Classic and NG operators to a potential issue with the fifth stage valve. Whereas the MOM called on operators to ensure valves weren’t sticking due to corrosion, the AD takes it a step further by requiring measurement of the clearance between the flapper bushings. Physical accomplishment of the AD is a “relatively easy task,” according to Gary Weissel, managing officer of Tronos Aviation Consulting, who happened to be planning a ferry flight for a 737-800 heading into conversion when the AD was issued. By his estimates, it takes about an hour of labor to ensure the valve’s flapper plates move freely, and to measure the gap between the flapper bushings. Cargo Facts believes the 737-800 is unit 30501 (ex-Shenzhen Airlines), which today left storage at Marana (MZJ) and was ferried to Miami (MIA), according to flight-tracking radar. The aircraft will soon be inducted for conversion by AEI at the Commercial Jet facility as part of a previously-announced three aircraft conversion order from BlackRock . For entities involved with 737s coming out of storage, or out of conversion, the AD will likely become part of routine inspections rather than an issue that will send fleets into maintenance. “This is not going to be a long and drawn-out process,” Weissel said. Still, some air frames slated for conversion, or coming out of conversion, could need valve replacements. Corrosion buildup in the valve is not a novel issue, according to Weissel, but the large number of 737s stored during the crisis and now reactivated appears to have drawn attention to the matter. When left unchecked, there’s a risk that a sticky valve could cause an engine to shut down in flight, according to the AD. While Weissel’s aircraft passed inspection, valve replacement would have otherwise delayed today’s ferry flight and sent the team off in search of a usable valve. Although larger 737 operators may have access to spare valves, as of this week, there weren’t many spares for sale on the West Coast. Used serviceable valves suitable as replacements cost between $30,000 and $70,000 per valve, according to Weissel.

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Conversion outlook: How many retired 767s will end up as freighters?

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