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While on vectors around WX flight crew changed speed mode and aircraft logic changed from altitude hold mode and drifted up 400 ft to set off altitude alerter and crew returned to assigned altitude.
| Attributes | |
| ACN | 279317 |
| Time | |
| Date | 199408 |
| Day | Thu |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | atc facility : iiu |
| State Reference | KY |
| Altitude | msl bound lower : 22000 msl bound upper : 22400 |
| Environment | |
| Flight Conditions | Mixed |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zid |
| Operator | common carrier : air carrier |
| Make Model Name | MD-81 |
| Operating Under FAR Part | Part 121 |
| Flight Phase | cruise other |
| Route In Use | enroute : on vectors |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 180 flight time total : 15000 flight time type : 2500 |
| ASRS Report | 279317 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance |
| Independent Detector | aircraft equipment other aircraft equipment : unspecified |
| Resolutory Action | flight crew : returned to intended course or assigned course flight crew : overcame equipment problem |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation other |
Narrative:
We were in cruise with the autoplt engaged at FL220. The autoplt was engaged in the 'performance cruise' mode. I switched it from 'performance cruise' to the 'speed select' mode to slow to turbulence penetration speed because we were turning to avoid areas of thunderstorm activity. Instead of engaging in the 'altitude hold' mode (which is normal), it went into the 'vertical speed' mode at 100 FPM rate of climb. We were both concentrating on WX avoidance and did not notice the slow climb rate. The altitude reached FL22.4 before I could correct back down to FL220. The WX was definitely a contributing factor as both the first officer and I were attempting to visually work our way through a large area of thunderstorms. The autoplt system should be changed so when you change from the 'performance cruise' mode to 'speed select' mode it stays in the 'altitude hold' mode.
Original NASA ASRS Text
Title: WHILE ON VECTORS AROUND WX FLC CHANGED SPD MODE AND ACFT LOGIC CHANGED FROM ALT HOLD MODE AND DRIFTED UP 400 FT TO SET OFF ALT ALERTER AND CREW RETURNED TO ASSIGNED ALT.
Narrative: WE WERE IN CRUISE WITH THE AUTOPLT ENGAGED AT FL220. THE AUTOPLT WAS ENGAGED IN THE 'PERFORMANCE CRUISE' MODE. I SWITCHED IT FROM 'PERFORMANCE CRUISE' TO THE 'SPD SELECT' MODE TO SLOW TO TURB PENETRATION SPD BECAUSE WE WERE TURNING TO AVOID AREAS OF TSTM ACTIVITY. INSTEAD OF ENGAGING IN THE 'ALT HOLD' MODE (WHICH IS NORMAL), IT WENT INTO THE 'VERT SPD' MODE AT 100 FPM RATE OF CLB. WE WERE BOTH CONCENTRATING ON WX AVOIDANCE AND DID NOT NOTICE THE SLOW CLB RATE. THE ALT REACHED FL22.4 BEFORE I COULD CORRECT BACK DOWN TO FL220. THE WX WAS DEFINITELY A CONTRIBUTING FACTOR AS BOTH THE FO AND I WERE ATTEMPTING TO VISUALLY WORK OUR WAY THROUGH A LARGE AREA OF TSTMS. THE AUTOPLT SYS SHOULD BE CHANGED SO WHEN YOU CHANGE FROM THE 'PERFORMANCE CRUISE' MODE TO 'SPD SELECT' MODE IT STAYS IN THE 'ALT HOLD' MODE.
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.