UNAUTH UNCOORD CLASS D AIRSPACE ENTRY WHEN THE PLT OF A BE35 ENTERS THE WRONG DEST IN HIS GPS; LATER NOT CHANGING THE PRESELECTED TWR FREQ TO ASH; NH.

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I NEEDED TO FLY MY PLANE TO ASH. I REGULARLY FLY TO BOTH ASH AND PSM. ANOTHER PLT WAS FLYING HIS BONANZA BEHIND ME; TO FLY ME HOME AFTER DROPPING OFF MY PLANE. I MISTAKENLY ENTERED PSM IN THE GPS. ABOUT 1/2 WAY INTO THE FLT; THE OTHER PLT CALLED FROM HIS AIRPLANE; WONDERING WHY WE WERE HEADED IN SLIGHTLY DIFFERENT DIRECTIONS. IT IS THEN THAT I CHANGED THE DEST TO ASH FROM PSM. HOWEVER; BEFORE TKOF; I HAD USED THE GPS TO RETRIEVE THE ATIS AND TWR FREQ FOR MY DEST; AS I USUALLY DO. WHEN IN MID FLT; I CHANGED THE DEST; I DID NOT UPDATE THE ATIS AND TWR FREQ ON THE GPS. WHEN I CALLED IN TO THE TWR; I WAS ACTUALLY TALKING TO PSM; BUT FLYING TO ASH. IT WAS NOT UNTIL I WAS ON SHORT FINAL AT ASH THAT I REALIZED MY ERROR; QUICKLY CHANGED TO ASH TWR; AND LANDED UNEVENTFULLY; WITH NO APPARENT TFC CONFLICTS. THE TWR CTLR TOLD ME TO CALL HIM. I DID. HE SAID HE WAS GOING TO RPT THE INCIDENT; AS HE WAS HAVING A VERY BAD DAY; WITH OTHER PROBS WITH OTHER ACFT ALL MORNING LONG. THE TWR CTLR WOULD NOT LET ME EXPLAIN WHY I WAS ON THE WRONG FREQ.