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.
Airwolf (a.k.a. Shadow of the Hawke) - S1-E1
Continuity mistake: When Stringfellow and Dominic first board Airwolf at the Libyan base, String gets in on Airwolf's right side, and pilots from there. When they land to rescue Gabrielle in the desert, he is in the left hand seat as the chopper lands and gets out of the left hand side.
Other mistake: General Butarra holds his pistol to St. John's head asking him where the diamonds are, dry firing it when he doesn't tell him, so the chamber must be empty. He then proceeds to load a magazine into the gun, but never chambers a round, and then proceeds to shoot the radio when it receives a storm alert broadcast. (00:28:40 - 00:29:11)
Ground Zero - S4-E14
Other mistake: When Hawke blows up Yahara's plane, we see that the video feed in the holding cell where Locke, Santini, and Rivers are is actually from a 3rd person perspective and that it continues, but according to previous dialogue (and video up to that point) the camera was installed on the plane, so once Hawke blew the plane up, there should have been no more video feed. (00:40:35)
Continuity mistake: Just as Santini lands his helicopter after his rear rotor was destroyed, Hawke gets into his jeep and drives off. The number plate (licence) is reversed and Hawke's steering wheel is on the right side like British vehicles are. The next shot you see the shot has been flipped the correct way with both plate and steering wheel on the left side. (00:24:14)
Continuity mistake: When Dominic is driving to Airwolf, in the long shot, he has shades. In the closeup, he doesn't.
Airwolf (a.k.a. Shadow of the Hawke) - S1-E1
Continuity mistake: When Hawke lands the helicopter during the film shoot, you see that the person in the left seat is handling the controls of the chopper normally, left hand on the collective, right one on the cyclic. In the next shot, the actor in the police uniform, sitting in the left seat, hides his face behind his arms and does not touch the controls at all.
Continuity mistake: When Hawke is first seen running on the ranch, his shirt is intact. A moment later, it's torn on the back, and the sleeve is ripped off.
Continuity mistake: Airwolf goes from normal flight to combat mode and back several times per episode when it's supposed to be in passive flight.
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
Character mistake: Dominic said the MIGs were coming in 015° but the readout says 105°. If they were at heading from 015, the triangles representing them would be in the upper right quadrant of the radar circle, close to the zero.
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.
Airwolf (a.k.a. Shadow of the Hawke) - S1-E1
Continuity mistake: In the courtyard of the palace, String has the weapons activated. A moment later, the gun pods are closed, then open again.
Continuity mistake: During the final battle Airwolf shoots a Bell UH-1. In the following explosion shot a Hughes OH-6 is blown up.
Other mistake: During the helicopter chase at the end a pilot can be seen in Airwolf's left seat although Hawke is sitting on the right side and Santini in the back.
Continuity mistake: For most of the flight shots, Mace is shown in the right seat. Part way through the chase, he's shown in the left seat, and everything is reversed.
Continuity mistake: When String tells Dominic about his plans to act on the phone call, Dominic says that things had been quiet for two months. When they're proceeding from liftoff in Airwolf, he said that three months hadn't harmed her, referring to Airwolf.
Continuity mistake: Flight scenes and especially dog fights seem to have no continuity at all. Altitude changes from scene to scene between extreme low-level to altitudes above 10,000 ft. and back. Airwolf's weapon bays are open, then closed, etc.
Answer: I don't think it's ever explained why Mac refused to tell Hawke where St. John is.