By Simon Hradecky, created Saturday, Jul 25th 2020 21:33Z, last updated Saturday, Jul 25th 2020 21:50Z

An Alaska Airlines Boeing 737-800, registration N569AS performing flight AS-1146 from Seattle,WA to Austin,TX (USA), was descending towards Austin, when the crew reported the left engine (CFM56) had failed. The crew performed the related checklist and reported on approach they were restarting the engine. The aircraft continued, on tower the crew reported they had lost engine #1 after all and continued for a safe landing on Austin's runway 17R.

The aircraft remained on the ground for 4 days for an engine change, then returned to service.

Alaska Airlines confirmed the flight suffered an engine shut down issue, the engine was replaced.

The aircraft had last flown on Jul 9th 2020 (JFK-SEA) prior to the occurrence, remained on the ground for 6 days and 4 hours before departing for the incident flight.

The occurrence is believed to be one of four mentioned by FAA as reason for Emergency Airworthiness Directive 2020-16-51. The FAA required airlines to check the engine bleed air 5th stage check valve on each engine for proper and free operation on all their Boeing 737 aircraft (classic and NG). The FAA reasoned:

This emergency AD was prompted by four recent reports of single-engine shutdowns due to engine bleed air 5th stage check valves being stuck open. Corrosion of the engine bleed air 5th stage check valve internal parts during airplane storage may cause the valve to stick in the open position. If this valve opens normally at takeoff power, it may become stuck in the open position during flight and fail to close when power is reduced at top of descent, resulting in an unrecoverable compressor stall and the inability to restart the engine. Corrosion of these valves on both engines could result in a dual-engine power loss without the ability to restart. This condition, if not addressed, could result in compressor stalls and dual-engine power loss without the ability to restart, which could result in a forced off-airport landing.

The FAA requires:

Any airplane that, for 7 or more consecutive days, has not been operated in flight is considered to be in storage.

(h) Inspections and Corrective Actions

(1) For any airplane that is in storage on or after the date of receipt of this AD, and any airplane that, as of the date of receipt of this AD, has been operated for 10 or fewer flight cycles since returning to service from the most recent period of storage: Before further flight, do the inspections specified in paragraphs (h)(1)(i) and (ii) of this AD on the engine bleed air 5th stage check valve on each engine. If any engine bleed air 5th stage check valve fails any inspection, replace that engine bleed air 5th stage check valve before further flight. For each engine bleed air 5th stage check valve that passes both inspections specified in paragraphs (h)(1)(i) and (ii) of this AD, do the actions 3 specified in paragraph (h)(2) of this AD on that engine bleed air 5th stage check valve before further flight.

(i) Rotate the flapper plates by hand at least 3 times. If the flapper plate moves smoothly, without signs of binding or sticking, from the fully closed position to the stop tube using gravity force alone, the engine bleed air 5th stage check valve has passed this inspection.

(ii) Measure the clearance between the flapper bushings at both locations on each engine bleed air 5th stage check valve. If the clearance between the flapper bushings is a minimum of 0.004 inch (0.102 mm) at both locations, the engine bleed air 5th stage check valve at that location has passed this inspection.

(2) For each engine bleed air 5th stage check valve that passes the inspections specified in paragraphs (h)(1)(i) and (ii) of this AD, do the inspections specified in paragraphs (h)(2)(i) through

(iii) of this AD before further flight on the engine bleed air 5th stage check valve on each engine. If any engine bleed air 5th stage check valve fails any of the inspections specified in paragraphs (h)(2)(i) through (iii) of this AD, replace that engine bleed air 5th stage check valve before further flight.

(i) Do a general visual inspection of the flapper bushings for signs of cracks, fractures, and missing bushing heads. If the flapper bushings do not show any signs of cracks, fractures, or missing bushing heads, the engine bleed air 5th stage check valve has passed this inspection. Signs of corrosion are not a cause for replacing the engine bleed air 5th stage check valve if the engine bleed air 5th stage check valve did not fail any of the inspections specified in paragraph (h)(1) of this AD.

(ii) Using only hand pressure, try to rotate the flapper bushings in the flapper plates. If the bushings do not rotate in the flapper plate, the engine bleed air 5th stage check valve has passed this inspection.

(iii) Do a general visual inspection of the check valve for signs of the flappers rubbing against the valve body. If the flappers do not show any signs of rubbing against the valve body, the engine bleed air 5th stage check valve has passed this inspection.


Track Related Flights on Airportia: AS1146