RWY INCURSION AND A CRITICAL GND CONFLICT AT A NON TWR ARPT WHEN ACFT X TAKES THE RWY IN FRONT OF AN UNANNOUNCED LNDG ACFT Y AT DTS; FL.

Narrative

AT APPROX XA30 I FILED AN IFR FLT PLAN TO DEPART DTS; DEST HEG (HERLONG ARPT; JACKSONVILLE; FL). UPON ARRIVING AT OUR DEST ARPT; ANOTHER PLT IN OUR PARTY WANTED TO FLY THE TRIP (HE IS CURRENT AND QUALIFIED IN THE ACFT) AND I AGREED TO LET HIM DO IT. I HAD FILED WITH ME AS PIC (I AM CURRENT AND QUALIFIED). I DID NOT CALL FSS OR ADVISE ATC WHEN WE CALLED FOR OUR CLRNC (I WAS ON FILE AS PIC) OF A CHANGE OF PIC. DESTIN IS AN UNCTLED ARPT WHERE YOU GET YOUR CLRNC FROM EGLIN AFB; AND THEN A RELEASE FOR DEP. AS WE TAXIED OUT FOR DEP; WE MONITORED BOTH ATC AND LCL UNICOM. WHEN WE FINISHED OUR RUN-UP; WE CALLED EGLIN APCH FOR RELEASE. WE WERE RELEASED FOR RWY 14 DEP. DURING OUR TAXI AND RUN-UP; WE MONITORED DTS UNICOM AND EGLIN APCH. WHEN WE WERE RELEASED; THE PF MADE A CALL ON UNICOM REGARDING OUR DEP ON RWY 14. WE LOOKED AND DID NOT SEE ANY ACFT EITHER ON BASE OR FINAL. WE DID NOT HEAR ANY RADIO TFC ON 122.8; BUT SEVERAL ACFT WERE ON EGLIN APCH WHEN WE TAXIED ONTO THE RWY. I SAW AN AIRPLANE OVERFLYING US ON RWY CTRLINE AND AT AN ALT OF 200-300 FT AGL. I DO NOT KNOW WHERE THIS ACFT CAME FROM; BUT IT WAS APPARENTLY ON FINAL WHEN WE ENTERED THE RWY. WE NEVER HEARD ANY RADIO TFC FROM ANYONE IN THE PATTERN OR ON FINAL. STANDARD PATTERNS AND PROPER RADIO PROC COULD HAVE PREVENTED THIS SIT.