A LR60 CREW INADVERTENTLY SQUAWKED 7500; WERE QUESTIONED ABOUT IT INFLT AND FINALLY MET AND QUESTIONED BY TSA AND LCL POLICE. THE CODE WAS SET ACCIDENTALLY BY A PRESET BUTTON.

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ON OCT/WED/05; WE TOOK OFF FROM ZZZ AT XA45 ON RTE TO ZZZ1; CLBED TO FL410 AND WERE CLRED BY CTR TO FLY DIRECT ABC. AT APPROX XB30; CTR CONTACTED US AND ASKED TO CONFIRM OUR SQUAWK CODE; AT WHICH THE SIC CONFIRMED 7500. I WAS DOING SOME PAPERWORK AND DID NOT PICK UP ON THE 7500 CODE; NOR DID SIC AT RESPONDING CONFIRMATION. 5 MINS LATER; WE CHANGED CTR FREQ AND THE NEW CTR ASKED US IF EVERYTHING WAS OK IN THE COCKPIT AND TO RECONFIRM SQUAWK OF 7500. THIS TIME I REALIZED THE SITUATION AND ASKED CTR TO GIVE ME THE SQUAWK CODE THAT WE SHOULD HAVE BEEN SQUAWKING; HE THEN GAVE ME CODE AND I EXPLAINED THAT WE SOMEHOW SQUAWKED 7500 ACCIDENTALLY; AND THAT EVERYTHING WAS NORMAL INFLT. HE THEN INSTRUCTED TO CHANGE CTR FREQ AND WE DID. THE NEXT CTR CTLR ASKED AGAIN IF WE WERE OK AND I REASSURED HIM THAT WE ACCIDENTALLY SQUAWKED 7500. WE CONTINUED ON OUR SCHEDULED FLT PLAN AND ALT AS REGULAR AND CHANGED CTR FREQ; AS INSTRUCTED. 3 ZAU CTLRS ASKED US THE REASON FOR THE 7500 SQUAWK AND I RESPONDED THAT WE DID IT ACCIDENTALLY. WE CONTINUED OUR FLT TO ZZZ1. UPON LNDG IN ZZZ1 AT XC30; I PROCEEDED TO TAXI TO RAMP WHERE WE PARKED. THE LCL POLICE AND TSA OFFICER MET US AND PROCEEDED TO SECURE THE ARR. I THEN WENT INSIDE THE FBO WITH POLICE AND TSA AGENTS. INSIDE; THEY ASKED ME AND SIC FOR OUR IDENT (PLTS LICENSE; D-LICENSE) AND WE WERE ASKED WHAT HAPPENED. I EXPLAINED THAT BY ACCIDENT I MUST OF PUSHED THE WRONG BUTTON ON THE FMS; COLLINS 850; WHICH HAS THE ATC BUTTON SIDE-BY-SIDE OF THE FLT PLAN BUTTON WHICH WE CONSTANTLY USE; AND THAT WE ACCIDENTALLY CAUSED THE SITUATION. I THEN CALLED CTR OPS MGR. I APOLOGIZED AND EXPLAINED TO HIM WHAT POSSIBLY HAPPENED; REASSURE IT WAS ACCIDENTAL. HE TOLD ME THAT HE WOULD HAVE TO FILE RPT AND WOULD INCLUDE MY EXPLANATION. I THEN REFOCUSED MY ATTN TO THE TSA AGENT; HE SAID THAT THEY WERE INFORMED THAT WE DID NOT COMMUNICATE FOR ABOUT 12 MINS. I TOLD HIM THAT WAS NOT THE CASE AND CALLED BACK ATC MGR. HE SPOKE TO ONE OF THE OFFICER AND EXPLAINED THAT WAS NOT THE CASE. THEY THEN RELEASED US AND WE WENT TO HOTEL. SINCE THIS INCIDENT WE HAVE NOW DELETED THE PRE-SELECT FREQ ON THE ATC BUTTON. THEY WERE PRE-SELECTED TO FREQ 1-7500; FREQ 2-7600; FREQ 3-7700. THIS ACFT IS NEW TO OUR FLEET AND WE WERE NOT AWARE OF THESE FREQ BEEN PRE-SELECTED ON THE ATC BUTTON. THEY ARE NOW SET AT 1200 ON ALL.