Using the lock orientation option on PlayBook you can lock the orientation of the device to portrait or landscape. See how to lock the screen orientation below.
Lock screen orientation of PlayBook
On BlackBerry PlayBook home screen, tap orientation lock icon from status bar and turn the switch on.
If you are inside any app then the status bar is hidden, to reveal the status bar swipe from top-left corner of the frame towards the center of the screen and use the orientation lock icon to lock the screen.