You're right Thunder Bird Five is only suggested that it's carried out every two years. If they are travelling well from the last overhaul then I don't do swing them.
If the compass has been done in a vacuum chamber at last overhaul normally they go 4 years.
Of course if they have had a engine change or major electrical change then we would do them. I don't know what Dicks situation was.
I still call them CAR 35 , Even now its called Part 21M. Force of habit I guess.
