Altitude deviation altitude overshot in descent.

Attributes
ACN	307456
Time
Date	199506
Day	Thu
Local Time Of Day	0601 To 1200
Place
Locale Reference	airport : lga
State Reference	NY
Altitude	msl bound lower : 2200 msl bound upper : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90
Operator	common carrier : air carrier
Make Model Name	Commercial Fixed Wing
Operating Under FAR Part	Part 121
Navigation In Use	Other Other
Flight Phase	descent other
Route In Use	approach : visual arrival other arrival star : star
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : instrument pilot : commercial pilot : atp pilot : flight engineer
Experience	flight time last 90 days : 200 flight time total : 15000 flight time type : 4000
ASRS Report	307456
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : flight engineer pilot : instrument pilot : commercial pilot : cfi pilot : atp
Experience	flight time last 90 days : 200 flight time total : 5000 flight time type : 3000
ASRS Report	307462
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : overshoot non adherence : clearance non adherence other other spatial deviation
Independent Detector	aircraft equipment other aircraft equipment : unspecified
Resolutory Action	flight crew : became reoriented flight crew : returned to intended course or assigned course flight crew : overcame equipment problem
Consequence	Other
Supplementary
Primary Problem	Aircraft
Air Traffic Incident	Pilot Deviation

Narrative:

Cleared to 2500 ft or above at diacs for the expressway visual to runway 31 at lga. Autoplt on, going direct diacs and had set to 2500 ft, using IAS descent mode. Using LNAV mode to go direct, and looking outside intensely to line up for visual approach. Suddenly heard 'altitude, altitude,' looked inside and saw 2200 ft on altimeter, descent rate still down. Made immediate recovery manually, disconnected autoplt and climbed back to 2500 ft. Lowest altitude seen was 2200 ft. I still do not know why this happened. I took no action to cause it as it should have been an automatic level off. I changed nothing that would have caused this to happen.

Original NASA ASRS Text

Title: ALTDEV ALT OVERSHOT IN DSCNT.

Narrative: CLRED TO 2500 FT OR ABOVE AT DIACS FOR THE EXPRESSWAY VISUAL TO RWY 31 AT LGA. AUTOPLT ON, GOING DIRECT DIACS AND HAD SET TO 2500 FT, USING IAS DSCNT MODE. USING LNAV MODE TO GO DIRECT, AND LOOKING OUTSIDE INTENSELY TO LINE UP FOR VISUAL APCH. SUDDENLY HEARD 'ALT, ALT,' LOOKED INSIDE AND SAW 2200 FT ON ALTIMETER, DSCNT RATE STILL DOWN. MADE IMMEDIATE RECOVERY MANUALLY, DISCONNECTED AUTOPLT AND CLBED BACK TO 2500 FT. LOWEST ALT SEEN WAS 2200 FT. I STILL DO NOT KNOW WHY THIS HAPPENED. I TOOK NO ACTION TO CAUSE IT AS IT SHOULD HAVE BEEN AN AUTOMATIC LEVEL OFF. I CHANGED NOTHING THAT WOULD HAVE CAUSED THIS TO HAPPEN.

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.