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An air carrier twin jet flight crew fails to notice the slow loss of altitude from that assigned while on ZBW frequency 30 mi southeast of bos, ma.
| Attributes | |
| ACN | 477250 |
| Time | |
| Date | 200006 |
| Day | Tue |
| Local Time Of Day | 0601 To 1200 |
| Place | |
| Locale Reference | navaid : bos.vortac |
| State Reference | MA |
| Altitude | msl bound lower : 10700 msl bound upper : 11000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : zbw.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | Large Transport, Low Wing, 2 Turbojet Eng |
| Operating Under FAR Part | Part 121 |
| Flight Plan | IFR |
| Aircraft 2 | |
| Navigation In Use | other other vortac |
| Flight Phase | descent : intermediate altitude |
| Route In Use | arrival : on vectors |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| Qualification | pilot : atp |
| Experience | flight time last 90 days : 150 flight time total : 11000 |
| ASRS Report | 477250 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| Qualification | pilot : multi engine pilot : instrument pilot : commercial |
| Events | |
| Anomaly | aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude non adherence : clearance other anomaly other |
| Independent Detector | aircraft equipment : altitude alert other controllera |
| Resolutory Action | controller : issued advisory flight crew : returned to assigned altitude |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft |
| Primary Problem | Aircraft |
| Air Traffic Incident | Pilot Deviation |
Narrative:
After aircraft leveled at 11000 ft MSL on autoplt, with altitude hold engaged, aircraft drifted down at about 300 FPM. Vertical speed for autoplt showed '00' but 300 FPM down on aircraft's vsi. At 10700 ft the altitude alert signaled an altitude deviation, followed shortly by ZBW asking what was our assigned altitude. We responded '11000 ft,' and had already started a correction at that time. There was no traffic near us. Other pilot duties (briefing of the approach plate, VFR traffic watch, discussion of traffic handling) plus the gradualness of the uncommanded descent, caused our not catching the deviation sooner.
Original NASA ASRS Text
Title: AN ACR TWIN JET FLC FAILS TO NOTICE THE SLOW LOSS OF ALT FROM THAT ASSIGNED WHILE ON ZBW FREQ 30 MI SE OF BOS, MA.
Narrative: AFTER ACFT LEVELED AT 11000 FT MSL ON AUTOPLT, WITH ALT HOLD ENGAGED, ACFT DRIFTED DOWN AT ABOUT 300 FPM. VERT SPD FOR AUTOPLT SHOWED '00' BUT 300 FPM DOWN ON ACFT'S VSI. AT 10700 FT THE ALT ALERT SIGNALED AN ALTDEV, FOLLOWED SHORTLY BY ZBW ASKING WHAT WAS OUR ASSIGNED ALT. WE RESPONDED '11000 FT,' AND HAD ALREADY STARTED A CORRECTION AT THAT TIME. THERE WAS NO TFC NEAR US. OTHER PLT DUTIES (BRIEFING OF THE APCH PLATE, VFR TFC WATCH, DISCUSSION OF TFC HANDLING) PLUS THE GRADUALNESS OF THE UNCOMMANDED DSCNT, CAUSED OUR NOT CATCHING THE DEV SOONER.
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.