A300
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation - Altitude Crossing Restriction Not Met; Deviation - Altitude Overshoot; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Flight Crew Returned To Clearance
Aircraft; Procedure
Flying LTOWN 6 into Memphis; aircraft was not going to make speed restriction at CLARK. We added more drag via spoilers at which time the nose abruptly pitched down (at 8;400 FT approximately). Selected ALT Hold on FCP. Aircraft would not level off so pilot flying (First Officer) disengaged autopilot and hand flew aircraft back to 8;000 FT. Note we went approximately 275 FT low. It needs to be noted that the A300 FMS is incapable of flying these STARS with any consistency. When it appears they may stay on profile they will always surprise you at the last second with some new exotic maneuver. Quite frankly; I'm tired of being set up for failure with procedures that are developed by someone who doesn't know anything about flying. Release the A300 from the requirement for flying these arrivals. Workload is increased exponentially and safety is reduced in kind.
Flying LTOWN 6 into MEM. Descending out of 9;000 FT for 8;000 FT; aircraft unable to maintain 210 KTS speed restriction. Extended speed brakes to slow down which resulted in a nose down pitch. Aircraft did not honor the 8;000 FT restriction at CLARK. As it approached 8;000 FT; I engaged ALT HOLD. Aircraft reacted too slowly and continued descent. I disconnected the autopilot and brought the aircraft back to 8;000 FT. Maximum deviation noted approximately 275 FT. Tighten up the tolerances the FMS allows before it reacts. Manually fly the autopilot (level change) and take the FMS out of the loop.
A300 flight crew laments the ability of the FMS to comply with RNAV arrival procedures.