Narrative:

I was the PNF. We were level at 2500 ft MSL, tracking the localizer for the ILS runway 35L aus. Approximately 8 mi from the airport, the autoplt and autothrust were engaged. After being cleared for the approach, the captain armed the approach and I set the missed approach altitude of 3000 ft. About 10 seconds later, the aircraft began an uncommanded climb, there were no abnormal indications on the FMA or ECAM. I believe the aircraft was trying to capture the GS from below. At about 3000 ft, the captain disconnected the autoplt and autothrust and began a descent back down to 2500 ft, continuing the approach without any further abnormalities. There were no questions from ATC. Supplemental information from acn 458843: captain flying, IMC in clouds and rain, level at assigned altitude of 2500 ft, on autoplt coupled approach ILS runway 35L to austin. Both autoplts on, position 3-5 NM outside creed FAF. First officer said 'setting missed approach to 3000 ft.' as the radio was busy, I did not mention that this was early as we had not yet captured the GS. Several seconds later, the autoplt commenced a steep pitch up uncommanded climb with autothrust at climb. As I disconnected autoplt/autothrust, I checked the FMA to see if open climb was enunciated. Indicating that the first officer may have inadvertently pulled the altitude knob on the FCU, and it was not. After GS intercept, the remainder of the manually flown approach and landing was normal. As the FMA did not change to altitude, indicating it was leveling at 3000 ft, it appeared to us that the autoplt may have been responding to a momentary dip in the GS signal (although we did not see one) with an aggressive 'fly up' command to capture the GS.

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Original NASA ASRS Text

Title: AT 2500 FT A 319-100 BEGINS UNCOMMANDED CLB DURING APCH TO AUS.

Narrative: I WAS THE PNF. WE WERE LEVEL AT 2500 FT MSL, TRACKING THE LOC FOR THE ILS RWY 35L AUS. APPROX 8 MI FROM THE ARPT, THE AUTOPLT AND AUTOTHRUST WERE ENGAGED. AFTER BEING CLRED FOR THE APCH, THE CAPT ARMED THE APCH AND I SET THE MISSED APCH ALT OF 3000 FT. ABOUT 10 SECONDS LATER, THE ACFT BEGAN AN UNCOMMANDED CLB, THERE WERE NO ABNORMAL INDICATIONS ON THE FMA OR ECAM. I BELIEVE THE ACFT WAS TRYING TO CAPTURE THE GS FROM BELOW. AT ABOUT 3000 FT, THE CAPT DISCONNECTED THE AUTOPLT AND AUTOTHRUST AND BEGAN A DSCNT BACK DOWN TO 2500 FT, CONTINUING THE APCH WITHOUT ANY FURTHER ABNORMALITIES. THERE WERE NO QUESTIONS FROM ATC. SUPPLEMENTAL INFO FROM ACN 458843: CAPT FLYING, IMC IN CLOUDS AND RAIN, LEVEL AT ASSIGNED ALT OF 2500 FT, ON AUTOPLT COUPLED APCH ILS RWY 35L TO AUSTIN. BOTH AUTOPLTS ON, POS 3-5 NM OUTSIDE CREED FAF. FO SAID 'SETTING MISSED APCH TO 3000 FT.' AS THE RADIO WAS BUSY, I DID NOT MENTION THAT THIS WAS EARLY AS WE HAD NOT YET CAPTURED THE GS. SEVERAL SECONDS LATER, THE AUTOPLT COMMENCED A STEEP PITCH UP UNCOMMANDED CLB WITH AUTOTHRUST AT CLB. AS I DISCONNECTED AUTOPLT/AUTOTHRUST, I CHKED THE FMA TO SEE IF OPEN CLB WAS ENUNCIATED. INDICATING THAT THE FO MAY HAVE INADVERTENTLY PULLED THE ALT KNOB ON THE FCU, AND IT WAS NOT. AFTER GS INTERCEPT, THE REMAINDER OF THE MANUALLY FLOWN APCH AND LNDG WAS NORMAL. AS THE FMA DID NOT CHANGE TO ALT, INDICATING IT WAS LEVELING AT 3000 FT, IT APPEARED TO US THAT THE AUTOPLT MAY HAVE BEEN RESPONDING TO A MOMENTARY DIP IN THE GS SIGNAL (ALTHOUGH WE DID NOT SEE ONE) WITH AN AGGRESSIVE 'FLY UP' COMMAND TO CAPTURE THE GS.

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.