Production Resource/Tool (PRT) Availability Check 
Use
What is Checked?
A status in the master record of every PRT category (material, PRT (misc.), document or equipment) determines whether a PRT is available or not. During the availability check the system statically checks this status to see whether the PRT is available for use or not.

The availability check for PRTs does not check whether other orders or networks require the same PRT at the same time.
In the case of PRTs with material masters, you can also conduct an availability check in the plant stock of the PRT. The system then check in the following stocks:
You specify in Customizing, whether the system only checks the status or whether it checks the status and the plant stock.
When is Availability Checked?
The availability check takes place either automatically or when you start it manually.
See also:
Evaluating the Availability Log for PRTs Classification of Production Resources/Tools