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B757-200 captain reported that during descent with the autopilot engaged the aircraft exceeded vmo (maximum operating limit speed).
| Attributes | |
| ACN | 1334858 |
| Time | |
| Date | 201602 |
| Local Time Of Day | 0001-0600 |
| Place | |
| Locale Reference | ZZZ.Airport |
| State Reference | US |
| Environment | |
| Flight Conditions | IMC |
| Light | Night |
| Aircraft 1 | |
| Make Model Name | B757-200 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | Descent |
| Flight Plan | IFR |
| Person 1 | |
| Function | Pilot Flying Captain |
| Qualification | Flight Crew Air Transport Pilot (ATP) |
| Experience | Flight Crew Last 90 Days 43 Flight Crew Total 10500 Flight Crew Type 1500 |
| Events | |
| Anomaly | Deviation - Procedural Published Material / Policy Deviation - Speed All Types |
Narrative:
Our clearance was to cross 40 east of ZZZ at 15000 ft. Autopilot was engaged; VNAV; on path; speed 325kts. Our radar indicated no precipitation before entering clouds at 22;000 ft. Upon entering the clouds the airspeed began to rise; so I extended speed brakes; airspeed slowed to below the commanded speed and the autothrottles increased to maintain this speed; at which point I stowed the speedbrakes; causing the a/south to increase rapidly. At this point I engaged V/south and airspeed continued to rise. I then disengaged the autopilot and initiated a climb to reduce the speed; but not before we had exceeded vmo/mmo by 25-30 KTS. With convective activity in the area I should have chosen a lower airspeed for our descent. All the weather that we were painting on our radar was 5-10 miles west; leading me to believe that we were ok with the chosen speed. I was unprepared for the speed in which this situation developed (15-20 sec). After reflection on the event; I believe I should have chosen flight level change instead of V/south or better yet disengage the autopilot altogether. I faced a situation where the autothrottles were commanding more thrust when what I needed was idle thrust.
Original NASA ASRS Text
Title: B757-200 Captain reported that during descent with the autopilot engaged the aircraft exceeded Vmo (maximum operating limit speed).
Narrative: Our clearance was to cross 40 east of ZZZ at 15000 ft. Autopilot was engaged; VNAV; on path; speed 325kts. Our radar indicated no precipitation before entering clouds at 22;000 ft. Upon entering the clouds the airspeed began to rise; so I extended speed brakes; airspeed slowed to below the commanded speed and the autothrottles increased to maintain this speed; at which point I stowed the speedbrakes; causing the A/S to increase rapidly. At this point I engaged V/S and airspeed continued to rise. I then disengaged the autopilot and initiated a climb to reduce the speed; but not before we had exceeded VMO/MMO by 25-30 KTS. With convective activity in the area I should have chosen a lower airspeed for our descent. All the weather that we were painting on our radar was 5-10 miles west; leading me to believe that we were OK with the chosen speed. I was unprepared for the speed in which this situation developed (15-20 Sec). After reflection on the event; I believe I should have chosen flight level change instead of V/S or better yet disengage the autopilot altogether. I faced a situation where the autothrottles were commanding more thrust when what I needed was idle thrust.
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.