Originally Posted by
ChrisJ800
Glider PIO's can be due to CG out of range, eg someone accidentally leaving a ballast weight in or in my case on one flight, a loose trim tab that moved every time I moved the elevator. Too fwd a CG can lead to you running out of elevator authority and too rear can lead to too twitchy elevator!
The usual cause of PIO landing a glider is insufficient airbrake.