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Md-11 first officer reported descending to a lower altitude after receiving a probable false stall warning at FL370 with normal airspeed indications.
| Attributes | |
| ACN | 1542793 |
| Time | |
| Date | 201805 |
| Local Time Of Day | 1801-2400 |
| Place | |
| Locale Reference | ZZZ.ARTCC |
| State Reference | US |
| Environment | |
| Flight Conditions | IMC |
| Aircraft 1 | |
| Make Model Name | MD-11 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Cruise |
| Flight Plan | IFR |
| Component | |
| Aircraft Component | Stall Warning System |
| Person 1 | |
| Function | First Officer Pilot Not Flying |
| Qualification | Flight Crew Instrument Flight Crew Air Transport Pilot (ATP) Flight Crew Multiengine |
| Events | |
| Anomaly | ATC Issue All Types Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance |
Narrative:
While in cruise at FL370; we received a stick shaker indication with corresponding red airspeed numbers on the airspeed indicator. It was confusing because we were 20-30 knots below the over-speed cue and 20-30 knots above the foot. At first; I assumed it was an error that would correct itself. After 15 or so seconds; we began to feel what we assumed was a buffet coincident with a high altitude stall. The autopilot and auto throttles disengaged. The captain commanded a lower altitude of FL350. The captain initially called for the 'airspeed unreliable' checklist which I started until we realized all 3 airspeeds indicated the same. I tried on multiple occasions to advise center to no avail. We started down anyway for safety. Eventually I was able to state our intentions. Since all visual indications seemed normal; we surmised it could be airframe ice. We added wings and tail to the engine ice we had already selected for most of the flight. Upon leveling at FL350; we still had some buffeting and we requested FL300. During that descent; the stick shaker stopped. The captain was able to reengage the auto-flight system and the buffeting ceased. Things seemed to normalize. Center asked for the nature of the emergency which I stated as stall indications. At FL300 and stable; we continued our flight uneventfully.it is unknown whether we picked up airframe icing which caused buffeting or there was a failure of a system i.e. Stall protection system.
Original NASA ASRS Text
Title: MD-11 First Officer reported descending to a lower altitude after receiving a probable false stall warning at FL370 with normal airspeed indications.
Narrative: While in cruise at FL370; we received a stick shaker indication with corresponding red airspeed numbers on the airspeed indicator. It was confusing because we were 20-30 knots below the over-speed cue and 20-30 knots above the foot. At first; I assumed it was an error that would correct itself. After 15 or so seconds; we began to feel what we assumed was a buffet coincident with a high altitude stall. The autopilot and auto throttles disengaged. The Captain commanded a lower altitude of FL350. The Captain initially called for the 'Airspeed Unreliable' checklist which I started until we realized all 3 airspeeds indicated the same. I tried on multiple occasions to advise Center to no avail. We started down anyway for safety. Eventually I was able to state our intentions. Since all visual indications seemed normal; we surmised it could be airframe ice. We added wings and tail to the engine ice we had already selected for most of the flight. Upon leveling at FL350; we still had some buffeting and we requested FL300. During that descent; the stick shaker stopped. The Captain was able to reengage the auto-flight system and the buffeting ceased. Things seemed to normalize. Center asked for the nature of the emergency which I stated as stall indications. At FL300 and stable; we continued our flight uneventfully.It is unknown whether we picked up airframe icing which caused buffeting or there was a failure of a system i.e. stall protection system.
Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.