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An MD80 captain reports this aircraft MCP altitude set knob operates differently from other MD80 MCP altitude set knobs causing an overshoot during descent.
| Attributes | |
| ACN | 667587 |
| Time | |
| Date | 200508 |
| Local Time Of Day | 1201 To 1800 |
| Place | |
| Locale Reference | navaid : slm.vor |
| State Reference | FO |
| Altitude | msl single value : 16000 |
| Environment | |
| Flight Conditions | VMC |
| Light | Daylight |
| Aircraft 1 | |
| Controlling Facilities | artcc : mmex.artcc |
| Operator | common carrier : air carrier |
| Make Model Name | MD-83 |
| Operating Under FAR Part | Part 121 |
| Navigation In Use | other vortac |
| Flight Phase | descent : intermediate altitude descent : approach |
| Flight Plan | IFR |
| Person 1 | |
| Affiliation | company : air carrier |
| Function | flight crew : captain oversight : pic |
| ASRS Report | 667587 |
| Person 2 | |
| Affiliation | company : air carrier |
| Function | flight crew : first officer |
| ASRS Report | 667588 |
| Events | |
| Anomaly | altitude deviation : overshoot non adherence : far non adherence : clearance |
| Independent Detector | aircraft equipment : altitude alert other controllera other flight crewa |
| Resolutory Action | controller : issued alert flight crew : returned to assigned altitude |
| Consequence | faa : reviewed incident with flight crew |
| Supplementary | |
| Problem Areas | Flight Crew Human Performance Aircraft |
| Primary Problem | Flight Crew Human Performance |
Narrative:
Aircraft 123 is the first aircraft I've flown where you must pull altitude set knob each time the altitude is changed; or it drops out of arm window. First officer and I were aware of it early in the flight. However; on descent into MMMX; first officer was off getting ATIS and I had the radios. I accepted a descent to 16000 ft then very shortly another clearance direct to mateos VOR. I forgot about the altitude not staying armed; failed to see the blank window and allowed aircraft to descend to about 15600 ft with an altitude alert. I climbed the aircraft back to 16000 ft. ATC noticed and called to remind us of clearance. We were not aware of any conflict. Conditions were clear VMC and there were no aircraft on TCASII. Supplemental information from acn 667588: we were flying an aircraft that required us to pull the altitude select knob every time the altitude was changed; otherwise it would disarm the altitude. I have not seen this on any other aircraft in the fleet.
Original NASA ASRS Text
Title: AN MD80 CAPT RPTS THIS ACFT MCP ALT SET KNOB OPERATES DIFFERENTLY FROM OTHER MD80 MCP ALT SET KNOBS CAUSING AN OVERSHOOT DURING DSCNT.
Narrative: ACFT 123 IS THE FIRST ACFT I'VE FLOWN WHERE YOU MUST PULL ALT SET KNOB EACH TIME THE ALT IS CHANGED; OR IT DROPS OUT OF ARM WINDOW. FO AND I WERE AWARE OF IT EARLY IN THE FLT. HOWEVER; ON DSCNT INTO MMMX; FO WAS OFF GETTING ATIS AND I HAD THE RADIOS. I ACCEPTED A DSCNT TO 16000 FT THEN VERY SHORTLY ANOTHER CLRNC DIRECT TO MATEOS VOR. I FORGOT ABOUT THE ALT NOT STAYING ARMED; FAILED TO SEE THE BLANK WINDOW AND ALLOWED ACFT TO DSND TO ABOUT 15600 FT WITH AN ALT ALERT. I CLBED THE ACFT BACK TO 16000 FT. ATC NOTICED AND CALLED TO REMIND US OF CLRNC. WE WERE NOT AWARE OF ANY CONFLICT. CONDITIONS WERE CLR VMC AND THERE WERE NO ACFT ON TCASII. SUPPLEMENTAL INFO FROM ACN 667588: WE WERE FLYING AN ACFT THAT REQUIRED US TO PULL THE ALT SELECT KNOB EVERY TIME THE ALT WAS CHANGED; OTHERWISE IT WOULD DISARM THE ALT. I HAVE NOT SEEN THIS ON ANY OTHER ACFT IN THE FLEET.
Data retrieved from NASA's ASRS site as of January 2009 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.