MD Helicopters is under Soviet mind-control and has been for a long timeHow else does the Soviet Union get enough MD 500 Defender helicopters to export them?
The Soviet Union had a secret factory in the Urals that produced reverse-engineered imitation MD HelicoptersIt's not like the Soviets cared that much about Intellectual Property.
Seasons 1-3 and Season 4 take place in (slightly) different continuities
Stringfellow Hawke is easily dupedArchangel could have had someone fly the Airwolf out of its lair anytime he wanted. But as long as Hawke could be talked into doing missions for him by letting him think he had the upper hand, why not?