From Grob Astir CS Maint Manual.

Inspection Procedures for Increase of Service Time
1. General
The results of fatigue tests of wing spar sections have demonstrated recently that the
service time of GRP gliders and motor gliders may be extended to 6000 hours, if for
each individual glider (in addition to the obligatory annual inspections) the airworthiness
is demonstrated according to a special multi-step inspection program particularly with
regard to the service life.
2. Time limits
When the glider has reached a service time of 3000 hours, an inspection must be done
in accordance with the inspection program mentioned under point 3. If the results of
this inspection are positive or if any defects found have been duly repaired, the service
time of the glider is extended by another 3000 hours to a total of 6000 hours (first
step).
The above inspection program must be repeated when the glider has reached a service
time of 6000 hours. If the results of this inspection are positive or if any defects found
have been duly repaired, the service time of the glider is extended to 7000 hours
(second step).
When the glider has reached a service time of 7000 hours, the above inspection
program again must be repeated. If the results of the inspection are still positive or if any
defects found have been duly repaired, the service time may be extended to a total of
8000 hours (third step).
The gradual extension of service life will be performed by steps of 1000 flight hours up
to maximum 12 000 flight hours at this time (4th – 7th stage).
Additionally at 9500, 10500, 11500 operating hours, inspection of the wing connection
bolts and main spars spigots must be performed accordance to Service Bulletin TM
306-30, latest edition, action 7.

And the multi step inspection is straight forward, simple. Just need form from type holder.