Plain English Meaning

A test that proves the aircraft's altitude-sensing plumbing and the device that sends altitude data to air traffic control are working correctly. It must be done every 24 calendar months for IFR flight in controlled airspace.

Full Definition

A required inspection and test of the aircraft's static pressure system and altitude-reporting encoder, performed by an appropriately rated technician, to verify accuracy and integrity within tolerances set by 14 CFR Part 43, Appendix E. For flight under instrument flight rules in controlled airspace, this must have been completed within the preceding 24 calendar months. The confirms the has no leaks and that the encoder altitude to air traffic control accurately.