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Air carrier medium large transport altitude deviation overshot during descent. Flight crew discovered altitude alert 3000 off clearance altitude after recovering from overshoot.
| Attributes | |
| ACN | 143890 |
| Time | |
| Date | 199004 |
| Day | Fri |
| Place | |
| Locale Reference | atc facility : ffu |
| State Reference | UT |
| Altitude | msl bound lower : 16600 msl bound upper : 17000 |
| Environment | |
| Flight Conditions | VMC |
| Aircraft 1 | |
| Controlling Facilities | artcc : zlc |
| Operator | common carrier : air carrier |
| Make Model Name | Medium Large Transport, Low Wing, 2 Turbojet Eng |
| Flight Phase | cruise other descent other |
| Route In Use | enroute airway : zlc |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : cfi pilot : flight engineer pilot : atp |
| Experience | flight time last 90 days : 100 flight time total : 4000 flight time type : 500 |
| ASRS Report | 143890 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Events | |
| Anomaly | aircraft equipment problem : critical altitude deviation : overshoot non adherence : clearance |
| Independent Detector | other flight crewa |
| Resolutory Action | flight crew : returned to intended course or assigned course |
| Consequence | Other |
| Supplementary | |
| Primary Problem | Flight Crew Human Performance |
| Air Traffic Incident | Pilot Deviation |
Narrative:
We were given a crossing restriction of 10 mi east of fairfield VOR at 17000' at 250 KTS. At 17000' the aircraft on autoplt and automatic altitude capture started to level off. I was monitoring the level off and everything appeared normal. As the aircraft reached 17100' it pitched down and started a descent again. At 16900' I disconnected the autoplt and the autothrottles and started a pitch-up recovery. To prevent sending any passengers or F/as falling through the cabin, the pull up was not abrupt. The level off was made at approximately 16600'-16700' and a climb back to 17000' was completed. When we checked the altitude window on the autoplt it was at 14000' not 17000'. Neither one of us could remember changing the altitude and we both remember setting 17000' and confirming the clearance to cross 10 east at 17000'. This type autoplt has had previous altitude changes that were not initiated by the crew and we were always watching it. We feel this was not a crew initiated altitude change but an inadvertent change by the autoplt.
Original NASA ASRS Text
Title: ACR MLG ALT DEVIATION OVERSHOT DURING DESCENT. FLT CREW DISCOVERED ALT ALERT 3000 OFF CLRNC ALT AFTER RECOVERING FROM OVERSHOOT.
Narrative: WE WERE GIVEN A XING RESTRICTION OF 10 MI E OF FAIRFIELD VOR AT 17000' AT 250 KTS. AT 17000' THE ACFT ON AUTOPLT AND AUTOMATIC ALT CAPTURE STARTED TO LEVEL OFF. I WAS MONITORING THE LEVEL OFF AND EVERYTHING APPEARED NORMAL. AS THE ACFT REACHED 17100' IT PITCHED DOWN AND STARTED A DSNT AGAIN. AT 16900' I DISCONNECTED THE AUTOPLT AND THE AUTOTHROTTLES AND STARTED A PITCH-UP RECOVERY. TO PREVENT SENDING ANY PAXS OR F/AS FALLING THROUGH THE CABIN, THE PULL UP WAS NOT ABRUPT. THE LEVEL OFF WAS MADE AT APPROX 16600'-16700' AND A CLB BACK TO 17000' WAS COMPLETED. WHEN WE CHKED THE ALT WINDOW ON THE AUTOPLT IT WAS AT 14000' NOT 17000'. NEITHER ONE OF US COULD REMEMBER CHANGING THE ALT AND WE BOTH REMEMBER SETTING 17000' AND CONFIRMING THE CLRNC TO CROSS 10 E AT 17000'. THIS TYPE AUTOPLT HAS HAD PREVIOUS ALT CHANGES THAT WERE NOT INITIATED BY THE CREW AND WE WERE ALWAYS WATCHING IT. WE FEEL THIS WAS NOT A CREW INITIATED ALT CHANGE BUT AN INADVERTENT CHANGE BY THE AUTOPLT.
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.