CL65 captured false GS on autoflt and climbed 500 ft above assigned altitude before disconnecting.

Attributes
ACN	582647
Time
Date	200306
Day	Mon
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : lga.airport
State Reference	NY
Altitude	msl bound lower : 2000 msl bound upper : 2500
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : n90.tracon
Operator	common carrier : air carrier
Make Model Name	Regional Jet CL65, Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 22
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : cfi pilot : multi engine pilot : instrument pilot : commercial
Experience	flight time last 90 days : 240 flight time total : 3800 flight time type : 2500
ASRS Report	582647
Person 2
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Events
Anomaly	aircraft equipment problem : critical altitude deviation : excursion from assigned altitude non adherence : published procedure non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	aircraft : automation overrode flight crew flight crew : overrode automation flight crew : returned to assigned altitude flight crew : returned to original clearance
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance Navigational Facility
Primary Problem	Navigational Facility
Air Traffic Incident	Pilot Deviation

Narrative:

While at 2000 ft, we were cleared for the ILS runway 22 at lga. The aircraft was set up for a coupled approach and I pushed the 'approach mode' on the flight control panel. The flight director captured the GS and localizer simultaneously. However, the GS then climbed and the aircraft followed. The aircraft climbed to approximately 2500 ft as I disconnected the autoplt and manually corrected back to 2000 ft to resume the approach uneventfully. The cause appeared to be the GS appearing too early and the autoplt/flight director capturing it prematurely. Time was also lost as we realized something wasn't normal and the time that I manually corrected the altitude deviation. Since this was the first time I have ever experienced this particular problem, it took me a few moments to analyze and correct...a pause that won't happen again if this were to occur in the future. This is yet another example why we should always scrutinize automation in the cockpit. It (automation) helps us tremendously, but it requires consistent monitoring.

Original NASA ASRS Text

Title: CL65 CAPTURED FALSE GS ON AUTOFLT AND CLBED 500 FT ABOVE ASSIGNED ALT BEFORE DISCONNECTING.

Narrative: WHILE AT 2000 FT, WE WERE CLRED FOR THE ILS RWY 22 AT LGA. THE ACFT WAS SET UP FOR A COUPLED APCH AND I PUSHED THE 'APCH MODE' ON THE FLT CTL PANEL. THE FLT DIRECTOR CAPTURED THE GS AND LOC SIMULTANEOUSLY. HOWEVER, THE GS THEN CLBED AND THE ACFT FOLLOWED. THE ACFT CLBED TO APPROX 2500 FT AS I DISCONNECTED THE AUTOPLT AND MANUALLY CORRECTED BACK TO 2000 FT TO RESUME THE APCH UNEVENTFULLY. THE CAUSE APPEARED TO BE THE GS APPEARING TOO EARLY AND THE AUTOPLT/FLT DIRECTOR CAPTURING IT PREMATURELY. TIME WAS ALSO LOST AS WE REALIZED SOMETHING WASN'T NORMAL AND THE TIME THAT I MANUALLY CORRECTED THE ALTDEV. SINCE THIS WAS THE FIRST TIME I HAVE EVER EXPERIENCED THIS PARTICULAR PROB, IT TOOK ME A FEW MOMENTS TO ANALYZE AND CORRECT...A PAUSE THAT WON'T HAPPEN AGAIN IF THIS WERE TO OCCUR IN THE FUTURE. THIS IS YET ANOTHER EXAMPLE WHY WE SHOULD ALWAYS SCRUTINIZE AUTOMATION IN THE COCKPIT. IT (AUTOMATION) HELPS US TREMENDOUSLY, BUT IT REQUIRES CONSISTENT MONITORING.

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.