AN IFR A36 PLT OVERSHOT HIS ASSIGNED ALT BECAUSE OF THE WORKLOAD AND UNFAMILIARITY WHEN THE GPS WOULD NOT ACCEPT A DIRECT TO A FIX COMMAND.

Narrative

I WAS ASSIGNED A HDG AND INSTRUCTED TO CLB TO 4000 FT. AS I WAS IN THE CLB; I RECEIVED ANOTHER INSTRUCTION TO GO DIRECT TO LAX. I BECAME DISTR WITH THE GPS TRYING TO ENTER THE NEW FIX AND NOTICED THAT I WAS AT 4400 FT. AT THAT TIME I STARTED A DSCNT AND THE CTLR CALLED AND SAID 'YOUR ASSIGNED ALT WAS 4000 FT; YOU MAY NOW CLB AND MAINTAIN 6000 FT.' I APOLOGIZED AND CONTINUED THE CLB TO 6000 FT. THE DISTR WAS THAT THE GPS WOULD NOT ACCEPT THE DIRECT LAX CHANGE BECAUSE THE FLT PLAN THAT I HAD LOADED WAS V23 TO LAX. THIS WAS WITH A GNS480. I TRIED REPEATED TIMES TO GET THE GPS TO TAKE THE FIX AND THEN REVERTED BACK TO A VOR TO GET A HDG. BY THEN I HAD LOST AWARENESS OF MY ALT. I ALSO FLY WITH A GARMIN GNS430 THAT DOES ALLOW THE PREVIOUS CHANGE SCENARIO TO WORK AND DID NOT REMEMBER THAT THE 480 WON'T ALLOW DIRECT TO A FIX THAT HAS BEEN ENTERED IN THE FLT PLAN WITH AN AIRWAY AS THE RTE. THE ABOVE POINTS OUT THAT WITH A MODERATE WORKLOAD AND A BIT OF UNFAMILIARITY WITH EQUIP; IT IS VERY EASY TO LOSE SITUATIONAL AWARENESS. IN RETROSPECT; I SHOULD HAVE STARTED A TURN IN THE GENERAL DIRECTION I KNEW TO BE TO LAX AND WAITED UNTIL I HAD LEVELED OFF AT 4000 FT BEFORE TRYING TO RESOLVE THE GPS ISSUE.