http://www.loc.gov/mods/v3 http://www.loc.gov/standards/mods/v3/mods-3-2.xsd
repair, overhaul, testing, and calibration of aircraft and aero-engine instruments; adjustment, installation, and compensation of compasses in aircraft; category "X" licence, by R. W. Sloley, and W. H. Coulthard.
The Aircraft engineers's handbook, no. 4