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37000 Feet | Browse and search NASA's Aviation Safety Reporting System |
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An air carrier flight crew descended below their assigned altitude inadvertently when they were deviating around thunderstorms while on the arrival into ord. The captain (PF) was briefing for the approach and did not notice that the autoplt altitude hold was not functioning as selected. The first officer detected the deviation during monitoring.
| Attributes | |
| ACN | 335149 |
| Time | |
| Date | 199605 |
| Day | Sun |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | atc facility : ord |
| State Reference | IL |
| Altitude | msl bound lower : 15700 msl bound upper : 16000 |
| Environment | |
| Flight Conditions | IMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : ord |
| Operator | common carrier : air carrier |
| Make Model Name | Commercial Fixed Wing |
| Operating Under FAR Part | Part 121 |
| Flight Phase | descent other |
| Route In Use | arrival other arrival star : star |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : commercial pilot : flight engineer pilot : atp pilot : instrument |
| Experience | flight time last 90 days : 162 flight time total : 13948 flight time type : 2364 |
| ASRS Report | 335149 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : instrument pilot : atp pilot : commercial |
| Experience | flight time last 90 days : 150 flight time total : 3000 flight time type : 400 |
| ASRS Report | 335960 |
| Events | |
| Anomaly | altitude deviation : excursion from assigned altitude |
| 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:
On knox arrival into ord we were descending on arrival while deviating around numerous thunderstorms on the arrival route. Our cleared altitude was 16000 ft. As we leveled off, I engaged the altitude hold on the autoplt, and began to brief the approach we were expecting. I turned around to read my approach plate, and began the brief when the first officer advised me we were off our assigned altitude at 15700 ft. I disengaged the autoplt and climbed back to 16000 ft. There were no other targets on the TCASII, and center seconds later cleared us to 11000 ft. I must not have gotten a good altitude hold lock when I engaged it, or I may have knocked it off when I turned around by bumping the control column. The first officer did a good job of monitoring the aircraft. I will be more cautious and make sure the autoplt stays in the mode I have selected. Supplemental information from acn 335960: old style autoplt -- no mode lights! The altitude hold lock must not have engaged.
Original NASA ASRS Text
Title: AN ACR FLC DSNDED BELOW THEIR ASSIGNED ALT INADVERTENTLY WHEN THEY WERE DEVIATING AROUND TSTMS WHILE ON THE ARR INTO ORD. THE CAPT (PF) WAS BRIEFING FOR THE APCH AND DID NOT NOTICE THAT THE AUTOPLT ALT HOLD WAS NOT FUNCTIONING AS SELECTED. THE FO DETECTED THE DEV DURING MONITORING.
Narrative: ON KNOX ARR INTO ORD WE WERE DSNDING ON ARR WHILE DEVIATING AROUND NUMEROUS TSTMS ON THE ARR RTE. OUR CLRED ALT WAS 16000 FT. AS WE LEVELED OFF, I ENGAGED THE ALT HOLD ON THE AUTOPLT, AND BEGAN TO BRIEF THE APCH WE WERE EXPECTING. I TURNED AROUND TO READ MY APCH PLATE, AND BEGAN THE BRIEF WHEN THE FO ADVISED ME WE WERE OFF OUR ASSIGNED ALT AT 15700 FT. I DISENGAGED THE AUTOPLT AND CLBED BACK TO 16000 FT. THERE WERE NO OTHER TARGETS ON THE TCASII, AND CTR SECONDS LATER CLRED US TO 11000 FT. I MUST NOT HAVE GOTTEN A GOOD ALT HOLD LOCK WHEN I ENGAGED IT, OR I MAY HAVE KNOCKED IT OFF WHEN I TURNED AROUND BY BUMPING THE CTL COLUMN. THE FO DID A GOOD JOB OF MONITORING THE ACFT. I WILL BE MORE CAUTIOUS AND MAKE SURE THE AUTOPLT STAYS IN THE MODE I HAVE SELECTED. SUPPLEMENTAL INFO FROM ACN 335960: OLD STYLE AUTOPLT -- NO MODE LIGHTS! THE ALT HOLD LOCK MUST NOT HAVE ENGAGED.
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.