I was at San Antonio International Airport, and I heard the tower trying to contact a lear 45. The controller told him to recycle the transponder a couple times but he didn’t respond until 20 minutes later. 
Might have been on the ground, they want you to use your Mode C on the ground at most larger airports nowadays
[quote=“flyboy97222”]
Might have been on the ground, they want you to use your Mode C on the ground at most larger airports nowadays[/quote]
That would be guess too. KSAT does have ground surveillance radar in use.