Narrative:

Our clearance had been 'descend to 9000', speed 210 KTS.' ord approach control was very busy. While descending at 210 KTS through approximately 10000', we were asked to slow to 170 KTS. Please note that the aircraft in question has a loud distracting voice warning system, which at 210 KTS and idle power warns you 'landing gear.' with the landing gear warning going off and the controller issuing a new speed at the same time, the 1000' call was to be made ('10000 for 9000'). Both the captain and I failed to notice that the altitude arming amber 'altitude' light was not on. Whether the captain failed to arm it or the altitude mode was disarmed by my use of the vertical speed mode of the FGS, is unknown. At 8700' the captain noticed our altitude deviation, at which time I turned off the autoplt and climbed back to the assigned altitude of 9000'. In my opinion, the altitude deviation was caused by a variety of distrs: 1) very busy ATC environment, 2) distracting warning horn for landing gear at 210 KTS, 3) no warning on aircraft of 1000' to level-off (it warns you only after altitude deviation, not before as on other aircraft in fleet), and 4) radio call from ATC to further slow aircraft to 170 KTS at critical time (descending from 10000 to 9000'). My recommendations: 1) require warning other than light (aural) of impending level-off, 2) remove 'landing gear' warning until flaps are at least down to 15 degrees and throttles idle, and 3) modify autoplts so that movement of vertical speed wheel while autoplt is in capture mode does not disengage capture mode. (Please note that our airlines is currently making this modification, but the aircraft we were on was not modified.)

Google
 

Original NASA ASRS Text

Title: REPORTER CITES A VARIETY OF REASONS FOR OVERSHOOTING ALT IN DESCENT. BOTTOM LINE IS THAT THE ALT CALLOUT WAS OMITTED. THE DISTRS OF GEAR WARNING, BUSY COCKPIT, COM PROCS AND NO ALT WARNING LIGHT MAY HAVE BEEN CONTRIBUTORY. PLT TECHNIQUE IN USE OF AUTOPLT WAS QUESTIONED BY REPORTER.

Narrative: OUR CLRNC HAD BEEN 'DSND TO 9000', SPD 210 KTS.' ORD APCH CTL WAS VERY BUSY. WHILE DSNDING AT 210 KTS THROUGH APPROX 10000', WE WERE ASKED TO SLOW TO 170 KTS. PLEASE NOTE THAT THE ACFT IN QUESTION HAS A LOUD DISTRACTING VOICE WARNING SYS, WHICH AT 210 KTS AND IDLE PWR WARNS YOU 'LNDG GEAR.' WITH THE LNDG GEAR WARNING GOING OFF AND THE CTLR ISSUING A NEW SPD AT THE SAME TIME, THE 1000' CALL WAS TO BE MADE ('10000 FOR 9000'). BOTH THE CAPT AND I FAILED TO NOTICE THAT THE ALT ARMING AMBER 'ALT' LIGHT WAS NOT ON. WHETHER THE CAPT FAILED TO ARM IT OR THE ALT MODE WAS DISARMED BY MY USE OF THE VERT SPD MODE OF THE FGS, IS UNKNOWN. AT 8700' THE CAPT NOTICED OUR ALT DEVIATION, AT WHICH TIME I TURNED OFF THE AUTOPLT AND CLBED BACK TO THE ASSIGNED ALT OF 9000'. IN MY OPINION, THE ALT DEVIATION WAS CAUSED BY A VARIETY OF DISTRS: 1) VERY BUSY ATC ENVIRONMENT, 2) DISTRACTING WARNING HORN FOR LNDG GEAR AT 210 KTS, 3) NO WARNING ON ACFT OF 1000' TO LEVEL-OFF (IT WARNS YOU ONLY AFTER ALT DEVIATION, NOT BEFORE AS ON OTHER ACFT IN FLEET), AND 4) RADIO CALL FROM ATC TO FURTHER SLOW ACFT TO 170 KTS AT CRITICAL TIME (DSNDING FROM 10000 TO 9000'). MY RECOMMENDATIONS: 1) REQUIRE WARNING OTHER THAN LIGHT (AURAL) OF IMPENDING LEVEL-OFF, 2) REMOVE 'LNDG GEAR' WARNING UNTIL FLAPS ARE AT LEAST DOWN TO 15 DEGS AND THROTTLES IDLE, AND 3) MODIFY AUTOPLTS SO THAT MOVEMENT OF VERT SPD WHEEL WHILE AUTOPLT IS IN CAPTURE MODE DOES NOT DISENGAGE CAPTURE MODE. (PLEASE NOTE THAT OUR AIRLINES IS CURRENTLY MAKING THIS MODIFICATION, BUT THE ACFT WE WERE ON WAS NOT MODIFIED.)

Data retrieved from NASA's ASRS site as of August 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.