Narrative:

RNAV Y approach to ZZZ. Configured; on profile; on autoplt; inside FAF. We were IMC and ZZZ WX was reported near minimums for this approach. On initial contact with tower we received a new altimeter setting which was 0.10 inches lower than what had been reported on ATIS. The airbus uses the manually entered altimeter setting to compute a GS-like descent path to minimums. Considering the WX; I decided to enter the new altimeter setting in the FMS. What neither I nor the captain (nor; from subsequent conversations; 2 of our check airmen) knew was that changing the altimeter setting would cause the autoplt to disconnect. I also didn't know that at the moment I was entering the new altimeter; the captain was pressing the button to give selection and control of airspeed to the FMS. After autoplt disconnect; the captain tried to re-engage the autoplt but was unable. He called for a go around and set climb thrust. Tower cleared us direct to the VOR and 3000 ft. We initiated the process of reconfiguring for the go around. About this time we got a low speed warning. Captain moved the thrust levers to toga. Tower called with heading changes; first 230 degrees; then 270 degrees. It was a busy; noisy and confusing time. With toga thrust we began a rapid climb. Captain then realized that the FMS was not controling the airspeed; that the flight directors were commanding a pitch attitude to yield 155 KTS; the last selected speed on approach. He manually selected a speed of approximately 210 KTS and began to level the aircraft. However; before control was fully regained we had climbed to nearly 4000 ft. This chain of events started with an unexpected autoplt disconnect and inability to re-engage. The distraction this caused diverted us from noticing that managed speed; which had been simultaneously selected; had not engaged. Teaching that altimeter entries in the FMGC during an RNAV approach will cause a disconnect would help. Getting a clearance to the ZZZ VOR starting the missed approach took me out of the loop at a critical time. The VOR isn't part of the approach so I was typing instead of monitoring. Using existing elements of the published missed approach procedure or headings would reduce workload in modern aircraft. Lastly; I'd like to see more simulator training addressing problems related to crew interface with automation.

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Original NASA ASRS Text

Title: AN A319 FO ENTERED AN 0.10 ALT CHANGE IN THE FMGC AS THE CAPT WAS ENGAGING MANAGED SPD ON AN IMC APCH. THE A/P DISCONNECTED RESULTING IN AN UNEXPECTED AND CONFUSING SERIES OF SPD AND ALT DEVIATION EVENTS.

Narrative: RNAV Y APCH TO ZZZ. CONFIGURED; ON PROFILE; ON AUTOPLT; INSIDE FAF. WE WERE IMC AND ZZZ WX WAS RPTED NEAR MINIMUMS FOR THIS APCH. ON INITIAL CONTACT WITH TWR WE RECEIVED A NEW ALTIMETER SETTING WHICH WAS 0.10 INCHES LOWER THAN WHAT HAD BEEN RPTED ON ATIS. THE AIRBUS USES THE MANUALLY ENTERED ALTIMETER SETTING TO COMPUTE A GS-LIKE DSCNT PATH TO MINIMUMS. CONSIDERING THE WX; I DECIDED TO ENTER THE NEW ALTIMETER SETTING IN THE FMS. WHAT NEITHER I NOR THE CAPT (NOR; FROM SUBSEQUENT CONVERSATIONS; 2 OF OUR CHK AIRMEN) KNEW WAS THAT CHANGING THE ALTIMETER SETTING WOULD CAUSE THE AUTOPLT TO DISCONNECT. I ALSO DIDN'T KNOW THAT AT THE MOMENT I WAS ENTERING THE NEW ALTIMETER; THE CAPT WAS PRESSING THE BUTTON TO GIVE SELECTION AND CTL OF AIRSPD TO THE FMS. AFTER AUTOPLT DISCONNECT; THE CAPT TRIED TO RE-ENGAGE THE AUTOPLT BUT WAS UNABLE. HE CALLED FOR A GAR AND SET CLB THRUST. TWR CLRED US DIRECT TO THE VOR AND 3000 FT. WE INITIATED THE PROCESS OF RECONFIGURING FOR THE GAR. ABOUT THIS TIME WE GOT A LOW SPD WARNING. CAPT MOVED THE THRUST LEVERS TO TOGA. TWR CALLED WITH HDG CHANGES; FIRST 230 DEGS; THEN 270 DEGS. IT WAS A BUSY; NOISY AND CONFUSING TIME. WITH TOGA THRUST WE BEGAN A RAPID CLB. CAPT THEN REALIZED THAT THE FMS WAS NOT CTLING THE AIRSPD; THAT THE FLT DIRECTORS WERE COMMANDING A PITCH ATTITUDE TO YIELD 155 KTS; THE LAST SELECTED SPD ON APCH. HE MANUALLY SELECTED A SPD OF APPROX 210 KTS AND BEGAN TO LEVEL THE ACFT. HOWEVER; BEFORE CTL WAS FULLY REGAINED WE HAD CLBED TO NEARLY 4000 FT. THIS CHAIN OF EVENTS STARTED WITH AN UNEXPECTED AUTOPLT DISCONNECT AND INABILITY TO RE-ENGAGE. THE DISTR THIS CAUSED DIVERTED US FROM NOTICING THAT MANAGED SPD; WHICH HAD BEEN SIMULTANEOUSLY SELECTED; HAD NOT ENGAGED. TEACHING THAT ALTIMETER ENTRIES IN THE FMGC DURING AN RNAV APCH WILL CAUSE A DISCONNECT WOULD HELP. GETTING A CLRNC TO THE ZZZ VOR STARTING THE MISSED APCH TOOK ME OUT OF THE LOOP AT A CRITICAL TIME. THE VOR ISN'T PART OF THE APCH SO I WAS TYPING INSTEAD OF MONITORING. USING EXISTING ELEMENTS OF THE PUBLISHED MISSED APCH PROC OR HDGS WOULD REDUCE WORKLOAD IN MODERN ACFT. LASTLY; I'D LIKE TO SEE MORE SIMULATOR TRAINING ADDRESSING PROBS RELATED TO CREW INTERFACE WITH AUTOMATION.

Data retrieved from NASA's ASRS site as of May 2009 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.