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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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Air carrier encounters mountain wave just prior to reaching assigned altitude. Altitude hold not properly engaged. Altitude deviation.
| Attributes | |
| ACN | 202911 |
| Time | |
| Date | 199202 |
| Day | Sat |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : gup |
| State Reference | NM |
| Altitude | msl bound lower : 35000 msl bound upper : 35400 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zab |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Navigation In Use | Other Other |
| Flight Phase | climbout : intermediate altitude cruise other |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 200 flight time total : 15000 flight time type : 250 |
| ASRS Report | 202911 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp pilot : commercial pilot : instrument |
| Events | |
| Anomaly | altitude deviation : overshoot inflight encounter : weather non adherence : clearance |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
En route climb from FL310 to FL350, reaching FL350, noticed vertical speed increasing to 1000 FPM and at FL351, started pushing nose over. Altitude capture had disengaged, altitude hold was pushed, aircraft continued climb. Throttles had gone to low lmt, altitude was now FL352. ATC asked our altitude, we confirmed the indication. Autoplt was disengaged, and aircraft was nosed over at FL354 and descended to FL350 with no further incident. ATC confirmed no conflict. Apparently we encountered a mountain wave just prior to reaching FL350, although flight conditions had been smooth. Both pilots were sure altitude had been armed, although at FL351, the 'arm' window of the FMA was blank. Apparently the 'altitude hold' button was not pushed firmly enough, as we continued to feel the aircraft rising (as opposed to the sensation of climbing), and I continued to overpwr the autoplt before the disconnect. The altitude excursion was noticed at +100 ft, and with the rate of climb of aircraft in the rise, with 142 passenger, seat belt sign off, carts in the aisle, I decided a gentle nose over was preferable to an abrupt 'hard over' just to remain at FL350. Flight conditions were clear and visibility unlimited. By the time the altitude warning occurred, the aircraft was already being corrected.
Original NASA ASRS Text
Title: ACR ENCOUNTERS MOUNTAIN WAVE JUST PRIOR TO REACHING ASSIGNED ALT. ALT HOLD NOT PROPERLY ENGAGED. ALTDEV.
Narrative: ENRTE CLB FROM FL310 TO FL350, REACHING FL350, NOTICED VERT SPD INCREASING TO 1000 FPM AND AT FL351, STARTED PUSHING NOSE OVER. ALT CAPTURE HAD DISENGAGED, ALT HOLD WAS PUSHED, ACFT CONTINUED CLB. THROTTLES HAD GONE TO LOW LMT, ALT WAS NOW FL352. ATC ASKED OUR ALT, WE CONFIRMED THE INDICATION. AUTOPLT WAS DISENGAGED, AND ACFT WAS NOSED OVER AT FL354 AND DSNDED TO FL350 WITH NO FURTHER INCIDENT. ATC CONFIRMED NO CONFLICT. APPARENTLY WE ENCOUNTERED A MOUNTAIN WAVE JUST PRIOR TO REACHING FL350, ALTHOUGH FLT CONDITIONS HAD BEEN SMOOTH. BOTH PLTS WERE SURE ALT HAD BEEN ARMED, ALTHOUGH AT FL351, THE 'ARM' WINDOW OF THE FMA WAS BLANK. APPARENTLY THE 'ALT HOLD' BUTTON WAS NOT PUSHED FIRMLY ENOUGH, AS WE CONTINUED TO FEEL THE ACFT RISING (AS OPPOSED TO THE SENSATION OF CLBING), AND I CONTINUED TO OVERPWR THE AUTOPLT BEFORE THE DISCONNECT. THE ALT EXCURSION WAS NOTICED AT +100 FT, AND WITH THE RATE OF CLB OF ACFT IN THE RISE, WITH 142 PAX, SEAT BELT SIGN OFF, CARTS IN THE AISLE, I DECIDED A GENTLE NOSE OVER WAS PREFERABLE TO AN ABRUPT 'HARD OVER' JUST TO REMAIN AT FL350. FLT CONDITIONS WERE CLR AND VISIBILITY UNLIMITED. BY THE TIME THE ALT WARNING OCCURRED, THE ACFT WAS ALREADY BEING CORRECTED.
Data retrieved from NASA's ASRS site as of July 2007 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.