The airborne auxiliary power units (APU) installed on aircraft for the purpose of generating and supplying a single type or combination of auxiliary electric, hydraulic, pneumatic or other power. Does not include generators, alternators, hydraulic pumps, etc., or their connecting systems which supply and deliver power to their respective aircraft systems. Use this code for reports of a general nature with insufficient 37 information to file in a specific JASC 4900 series code, or for reports which involve two or more APU systems. An entry "APU" is acceptable if no specific part is reported. The APU as well as aircraft make and model should be reported if known.