A319 flight crew has erroneous GS indication and the aircraft 'chases' the GS on approach to pit.

Attributes
ACN	591910
Time
Date	200308
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	navaid : mmj.vortac
State Reference	PA
Altitude	msl bound lower : 6000 msl bound upper : 6500
Environment
Flight Conditions	IMC
Light	Daylight
Aircraft 1
Controlling Facilities	tracon : pit.tracon
Operator	common carrier : air carrier
Make Model Name	A319
Operating Under FAR Part	Part 121
Navigation In Use	ils localizer & glide slope : 28r
Flight Phase	descent : approach
Route In Use	approach : instrument precision
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : captain oversight : pic
Qualification	pilot : atp
ASRS Report	591910
Person 2
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp pilot : multi engine pilot : flight engineer
ASRS Report	591911
Events
Anomaly	altitude deviation : excursion from assigned altitude other anomaly
Independent Detector	aircraft equipment other aircraft equipment : glide slope indicator other flight crewa other flight crewb
Resolutory Action	flight crew : overrode automation flight crew : overcame equipment problem
Supplementary
Problem Areas	Navigational Facility Flight Crew Human Performance Aircraft
Primary Problem	Flight Crew Human Performance

Narrative:

We were flying an airbus 319. We were at 6000 ft MSL on the localizer for ILS runway 28R at pit. We were cleared for the approach and 'approach' was armed. Around +/-23 DME the GS came down rapidly from the top of the scale. GS captured and immediately the GS went back up to the top of scale. The aircraft followed the GS up and autothrust added full power rapidly. At approximately +/-6500 ft MSL I disconnected the autoplt and autothrust to get back down to altitude (6000 ft). Now above GS and hand flown in a gradual descent I told first officer to reengage autoplt and autothrust. The aircraft started climbing and accelerating again. Disconnected, autoplt, autothrust, flight director and approach mode. Hand flew back down towards GS. Reset altitude window to 4000 ft and open descent. Caught GS finally from about somewhere around cofee fix, reconnected autoplt and autothrust and autoplt flew rest of normal ILS to runway 28R. I believe we had a false capture of the GS outside the normal range of GS intercept. There have been some reports of this happening before, but I thought airbus had fixed it.

Original NASA ASRS Text

Title: A319 FLT CREW HAS ERRONEOUS GS INDICATION AND THE ACFT 'CHASES' THE GS ON APCH TO PIT.

Narrative: WE WERE FLYING AN AIRBUS 319. WE WERE AT 6000 FT MSL ON THE LOC FOR ILS RWY 28R AT PIT. WE WERE CLRED FOR THE APCH AND 'APCH' WAS ARMED. AROUND +/-23 DME THE GS CAME DOWN RAPIDLY FROM THE TOP OF THE SCALE. GS CAPTURED AND IMMEDIATELY THE GS WENT BACK UP TO THE TOP OF SCALE. THE ACFT FOLLOWED THE GS UP AND AUTOTHRUST ADDED FULL PWR RAPIDLY. AT APPROX +/-6500 FT MSL I DISCONNECTED THE AUTOPLT AND AUTOTHRUST TO GET BACK DOWN TO ALT (6000 FT). NOW ABOVE GS AND HAND FLOWN IN A GRADUAL DSCNT I TOLD FO TO REENGAGE AUTOPLT AND AUTOTHRUST. THE ACFT STARTED CLBING AND ACCELERATING AGAIN. DISCONNECTED, AUTOPLT, AUTOTHRUST, FLT DIRECTOR AND APCH MODE. HAND FLEW BACK DOWN TOWARDS GS. RESET ALT WINDOW TO 4000 FT AND OPEN DSCNT. CAUGHT GS FINALLY FROM ABOUT SOMEWHERE AROUND COFEE FIX, RECONNECTED AUTOPLT AND AUTOTHRUST AND AUTOPLT FLEW REST OF NORMAL ILS TO RWY 28R. I BELIEVE WE HAD A FALSE CAPTURE OF THE GS OUTSIDE THE NORMAL RANGE OF GS INTERCEPT. THERE HAVE BEEN SOME RPTS OF THIS HAPPENING BEFORE, BUT I THOUGHT AIRBUS HAD FIXED IT.

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.