021-Airframes and systems
Like for the 010, a good start would be to remind you the 021 JAR-FCL's learning objectives.
Reminder: JAR-FCL stands for Joint Aviation Requirements for Flight Crew Licensing.
We're talking here about technical texts elaborated by the different JAA working groups which don't have international scale law value.
It is each JAA' state (Joint Aviation Authorities - European Union members that ratified the Rome treaty) that commit themselves to enforce the JAR by introducing their own national rules (with their own national particularities).
For a stronger headache, you can consult: