Narrative:

I have just installed 2 garmin 430 units and 1 sandel EFIS system connected to A300 bendix 300 autoplt. While cruising at 15000 ft, entered an approach to cfd (coulter field, bryan, tx). This is a VOR/DME approach with a DME arc. Entered procedure, selected load -- held active route. Approximately 1 min later, altitude hold on autoplt tripped off. Autoplt tripped off. Aircraft went into a steep but even descent. Manual command of aircraft was taken to stop descent. Center called as I called them, asked why deviation of altitude. I responded with short description of autoplt disconnect. No further comment from center. I canceled IFR at that time. Would recommend that all pilots upgrading to dual/FM GPS's connected to each other with sandel equipment use extra care in initial flts as, after talking to our installer, some of the features don't always react. All the new radio equipment is 1999. Autoplt is 1979. System appears to work well together. Recommend very careful flight watch until familiar with use of system. Callback conversation with reporter revealed the following information: on callback reporter states that this was the first flight after installing this new equipment on his aircraft. That reading the books and actually flying the aircraft are two different things. He expects that after a few hours with the new equipment will greatly reduce the learning curve.

Related reports:

Google
 

Original NASA ASRS Text

Title: AN ATP RATED PLT A CHEYENNE TURBOPROP NEAR BYRAN, TX, DEVIATED FROM HIS ASSIGNED ALT.

Narrative: I HAVE JUST INSTALLED 2 GARMIN 430 UNITS AND 1 SANDEL EFIS SYS CONNECTED TO A300 BENDIX 300 AUTOPLT. WHILE CRUISING AT 15000 FT, ENTERED AN APCH TO CFD (COULTER FIELD, BRYAN, TX). THIS IS A VOR/DME APCH WITH A DME ARC. ENTERED PROC, SELECTED LOAD -- HELD ACTIVE RTE. APPROX 1 MIN LATER, ALT HOLD ON AUTOPLT TRIPPED OFF. AUTOPLT TRIPPED OFF. ACFT WENT INTO A STEEP BUT EVEN DSCNT. MANUAL COMMAND OF ACFT WAS TAKEN TO STOP DSCNT. CTR CALLED AS I CALLED THEM, ASKED WHY DEV OF ALT. I RESPONDED WITH SHORT DESCRIPTION OF AUTOPLT DISCONNECT. NO FURTHER COMMENT FROM CTR. I CANCELED IFR AT THAT TIME. WOULD RECOMMEND THAT ALL PLTS UPGRADING TO DUAL/FM GPS'S CONNECTED TO EACH OTHER WITH SANDEL EQUIP USE EXTRA CARE IN INITIAL FLTS AS, AFTER TALKING TO OUR INSTALLER, SOME OF THE FEATURES DON'T ALWAYS REACT. ALL THE NEW RADIO EQUIP IS 1999. AUTOPLT IS 1979. SYS APPEARS TO WORK WELL TOGETHER. RECOMMEND VERY CAREFUL FLT WATCH UNTIL FAMILIAR WITH USE OF SYS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: ON CALLBACK RPTR STATES THAT THIS WAS THE FIRST FLT AFTER INSTALLING THIS NEW EQUIP ON HIS ACFT. THAT READING THE BOOKS AND ACTUALLY FLYING THE ACFT ARE TWO DIFFERENT THINGS. HE EXPECTS THAT AFTER A FEW HOURS WITH THE NEW EQUIP WILL GREATLY REDUCE THE LEARNING CURVE.

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.