1. Doing a circling approach and on very short final you have to do a go around. What climb gradient do i have to make when i fly the opposite ils or approach sector up to the msa? Any restrictions single engine? Somebody told me 5,5% but didnt know where he got this value from
Off a circling approach you fly the missed approach for the approach you have just flown, so I fail to understand why you would want to work out a gradient for something that you would not do? While you would probably be safe flying the missed approach procedure for the opposite runway, you would be making it up "on the fly", so would not be flying a published procedure i.e. you are on your own!
3.Holding with the 737. Programmed and prior entering the hold the FMS message "Unable hold airspace" appears. Any explanation on that?
It usually comes up with "UNABLE HOLD AIRSPACE" because the aircraft is too fast for the hold to be flown with the LNAV aob limits.