PA-34-200 Seneca I
Flight Crew Private; Flight Crew Instrument; Flight Crew Multiengine
Flight Crew Last 90 Days 5; Flight Crew Total 350; Flight Crew Type 35
Workload; Time Pressure; Confusion; Human-Machine Interface; Distraction
Deviation - Altitude Excursion From Assigned Altitude; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Executed Go Around / Missed Approach
Altitude deviation of approximately 350-400 feet during autopilot-flown published MAP GPS Runway 05. Deviation took place 'between' ATC handoff from center to approach - neither controller raised/mentioned any concern about the altitude and no vertical separation was reported as lost. Reprogramming FMS (deleting current MAP; adding new destination) also was required during this hand-off. Altitude of 4;000 set and armed in KFC-150 AP (AP altitude functions had been somewhat erratic on earlier approach). Altitude capture function did not hold 4;000 MSL - continued climb noted and I immediately disengaged AP and hand-flew the aircraft to assigned altitude. CAVEATS and recommendations: 1) The installed AP is 16+ years old and is interfacing with new technology navigators and 3-screen PFD/MFDs. The FMS/interfacing displays have developed faster than many 'older' autopilots common in GA today. This might be considered as part of testing/development (and perhaps a FAA WINGS computer training session related to these interfaces!) - how new panel technology will interface with older APs. That info is certainly not in the older AP manuals! 2) The ATC hand-off from center to approach took place during the busy MAP procedure (prior to reaching published MAP holding waypoint). Granted; this is no big deal for a crewed airplane as the Pilot Not Flying (PNF) normally handles the COM/NAV/FMS; etc....hand-offs at this time for single-pilot GA are very difficult. Waiting an extra minute or two for the pilot to enter the hold/level off/reduce workload and then discuss next approach or other options may help prevent task saturation in single-pilot IFR operations. Perhaps this is information that might be helpful to controllers when dealing with smaller GA aircraft (single pilot) on a MAP procedure.  Thank you for allowing me to share my thoughts and kudos to this excellent reporting program.
A PA-34 pilot reported his aircraft's sixteen year old autopilot is interfaced with a new technology FMS. As center handed him off to approach; he was reprogramming for a practice GPS approach but his autopilot failed to capture an altitude resulting an overshoot and very high workload. Single pilot operations with mixed new and old technology creates special demands.