There are 4 different Learjets in the first flight sequence. First it has 3 side windows, then 1, then 2, 3 again, 6 (with missing wingtip fuel tanks), 1, 3, 1.
Laurence Thurmond played by John Heard is seen flying a jet to presumably let off a little steam while Crockett simultaneously "visits his therapist" at a gun range. Unfortunately there are two different jets being flown, a Learjet 25A (registration number N24PJ) and a Learjet 24D (registration number N464CL).