Revealing mistake: When String uses Airwolf's rotor wash to blow over the pickup, when the camera is on the truck, you can see a cable pulling the truck up from the right side.
Proof Through the Night - S1-E4
Revealing mistake: As Airwolf flies at high speed across the countryside to get away from Russia, the shadow of the camera chopper can be seen on the ground, rather than the Bell 222 Airwolf.
Proof Through the Night - S1-E4
Revealing mistake: As Hawke uses the Star Light Amplification System to see where he's flying, the readout shows what he's looking at. The electronic compass readout at the top of the display doesn't move, even though the picture shows that he's constantly twisting and turning, following the terrain.
Proof Through the Night - S1-E4
Revealing mistake: As the camera flies over the ranch and house (simulating Airwolf's flight), the camera chopper's left skid is visible in the lower left corner of the shot. Airwolf is a Bell 222 with added features, and doesn't have skids.
Airwolf (a.k.a. Shadow of the Hawke) - S1-E1
Revealing mistake: As the camera has a closeup on Moffet driving the jeep, the shadow of the camera rig plays across the windshield.
Answer: I don't think it's ever explained why Mac refused to tell Hawke where St. John is.