People say the Nikon F4 has poor auto-focus but I've honestly never had much problem with it when using prime lenses in good light ... except for this day. Most of the helicopter shots were just about at the infinity mark on the 300mm lens and combined with the general haziness of the day the F4 had a really difficult time deciding what do with the focus. I might try the N70 next time.
This shoot also made me wish I had a 1.4x teleconverter