2025-09 · NASA ASRS report 2289401
B737 flight crew reported a master caution for COWL ANTI ICE number 2 engine. Priority handling and a divert followed.
Enroute ZZZ1 - ZZZ2 FL390 ZZZ center Master Caution COWL ANTI ICE number 2Me PF PM ran QRH I reduced the number 2 thrust lever to idle per the checklist.We began a descent determined SE altitude of FL260.QRH ended with light extinguished scenario only but light remained on.Call me in ACARS and spoke with maintenance control and dispatcher.Maintenance control would only say follow flight manual and I'll email any ideas.We requested priority handling; decided to divert to ZZZ with dispatcher concurrence.Briefed FA's and PAXs no evacuation but Crash and Fire Rescue (CFR) vehicles. I remained PF due to experience level with regard to single engine at altitude.We revisited the QRH and discussed options. Due to the light remaining on and a suspected faulty sensor (all engine indications normal); we evaluated the risk of advancing thrust on that engine to be less than the risk of a single engine approach and landing with possible single engine go around. The QRH does not address the scenario we had where the light remains illuminated when thrust is at idle.PM reprogrammed the FMC and briefed the approach and ran the descent checklist. We were given box vectors until ready to commence the approach. We observed continued normal engine indications. We briefed a single engine contingency. When ready for the approach I advanced thrust on engine number 2 observing normal indications. We checked weather and NOTAMs; spoke with CFR on tower frequency asking that they monitor engine number 2 and follow us to the gate unless we had non normal engine indications. In that case we would stop the aircraft and assess. We proceeded with a flaps 30 AB3 landing on XX backed up by the ILS. Normal landing and progressive taxi to gate XX. Landed under structural landing weight. At the gate I addressed passengers; spoke with CFR; inspected engine cowl; and called the Chief Pilot.Added MX discrepancy in logbook.Debriefed crew.
Approx. 100 miles SW of ZZZ at FL390 master caution for number 2 engine (right engine) cowl anti-ice light. No other irregularities. Ran FM non-normal procedure; ENGINE COWL ANTI-ICE. The light remained illuminated with engine thrust at idle. Descended and diverted into ZZZ after communicating with maintenance control & Dispatch. Requested priority handling with ZZZ center and landed uneventfully at ZZZ. Approach and landing were flown dual engine with a planned single-engine go around briefed and ready. Therefore; minimal thrust was used on the affected engine during approach and landing. Taxied clear and taxied to gate with crash; fire rescue following. Normal engine shutdown procedures after arriving at the gate.Recommend expansion of the procedure to include information that will address if the light remains illuminated after retarding the thrust lever to idle.Interaction with maintenance control was not useful during the FM non-normal ENGINE COWL ANTI-ICE procedure. 'Complete FM procedure and no further information'.
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Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.
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