Altitude excursion deviation occurs as air carrier mdt atuoplt fails to capture armed altitude.

Attributes
ACN	147164
Time
Date	199005
Day	Sat
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : jfk
State Reference	NY
Altitude	msl bound lower : 2200 msl bound upper : 3000
Environment
Flight Conditions	Mixed
Light	Night
Aircraft 1
Controlling Facilities	tracon : n90 tower : yyz
Operator	common carrier : air carrier
Make Model Name	Medium Transport
Flight Phase	cruise other cruise other
Route In Use	arrival other enroute : on vectors
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
Experience	flight time last 90 days : 210 flight time total : 3800
ASRS Report	147164
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : excursion from assigned altitude altitude deviation : overshoot non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued new clearance flight crew : returned to intended course or assigned course other
Consequence	Other
Supplementary
Primary Problem	Ambiguous
Air Traffic Incident	Pilot Deviation

Narrative:

While on vectors for an ILS runway 13L at jfk, we were instructed to descend and maintain 3000'. We vacated 7000' and began inrange checklist. Aircraft was being flown on autoplt (autoplt is equipped with altitude capture). As I was completing the approach briefing, approach calmly advised us to climb and maintain 3000'. (No sense of urgency in his voice). We had allowed the aircraft to descend to 2200'. I immediately disconnected autoplt and climbed back to 3000'. (The autoplt indicated an altitude capture, but it continued to descend). The flight continued west/O further occurrence. The controller never mentioned anything more about the altitude excursion. I don't think that our altitude excursion resulted in any traffic conflicts. This occurrence could have easily been avoided by monitoring the aircraft's progress throughout the descent. My previous experience in this aircraft type had never witnessed it not capture an altitude. This good reliability of the autoplt may have left some complacency within me. The aircraft isn't equipped with an aural altitude alert, but rather with a dimly lit light. This occurrence wouldn't be a problem in the future with proper altitude awareness and constant monitoring of the aircraft. I believe that we wouldn't have busted our by 800' if our aircraft was equipped with an aural warning.

Original NASA ASRS Text

Title: ALT EXCURSION DEVIATION OCCURS AS ACR MDT ATUOPLT FAILS TO CAPTURE ARMED ALT.

Narrative: WHILE ON VECTORS FOR AN ILS RWY 13L AT JFK, WE WERE INSTRUCTED TO DSND AND MAINTAIN 3000'. WE VACATED 7000' AND BEGAN INRANGE CHKLIST. ACFT WAS BEING FLOWN ON AUTOPLT (AUTOPLT IS EQUIPPED WITH ALT CAPTURE). AS I WAS COMPLETING THE APCH BRIEFING, APCH CALMLY ADVISED US TO CLB AND MAINTAIN 3000'. (NO SENSE OF URGENCY IN HIS VOICE). WE HAD ALLOWED THE ACFT TO DSND TO 2200'. I IMMEDIATELY DISCONNECTED AUTOPLT AND CLBED BACK TO 3000'. (THE AUTOPLT INDICATED AN ALT CAPTURE, BUT IT CONTINUED TO DSND). THE FLT CONTINUED W/O FURTHER OCCURRENCE. THE CTLR NEVER MENTIONED ANYTHING MORE ABOUT THE ALT EXCURSION. I DON'T THINK THAT OUR ALT EXCURSION RESULTED IN ANY TFC CONFLICTS. THIS OCCURRENCE COULD HAVE EASILY BEEN AVOIDED BY MONITORING THE ACFT'S PROGRESS THROUGHOUT THE DSNT. MY PREVIOUS EXPERIENCE IN THIS ACFT TYPE HAD NEVER WITNESSED IT NOT CAPTURE AN ALT. THIS GOOD RELIABILITY OF THE AUTOPLT MAY HAVE LEFT SOME COMPLACENCY WITHIN ME. THE ACFT ISN'T EQUIPPED WITH AN AURAL ALT ALERT, BUT RATHER WITH A DIMLY LIT LIGHT. THIS OCCURRENCE WOULDN'T BE A PROB IN THE FUTURE WITH PROPER ALT AWARENESS AND CONSTANT MONITORING OF THE ACFT. I BELIEVE THAT WE WOULDN'T HAVE BUSTED OUR BY 800' IF OUR ACFT WAS EQUIPPED WITH AN AURAL WARNING.

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.