SAE AS942A

The instrument system specified shall accept an input of static pressure and in some equipment other inputs that contribute altitude information to provide a visual indication of pressure altitude. If equipped with an automatic correction mechansim, it shall indicate by a positive means when the automatic correction mechanism is not in use. If the static source pressure error compensating mechanism is operational it shall be functional throughout the required operating envelope of the particular aircraft. Each aircraft type has its own static source error data which shall be obtained from the airframe manufacturer's certified data. when a central air data computer is used in the altimeter system, the CADC shall be certified to its own governing document and the altimeter system (CADC and display) shall comply with the requirements of this document.

The purpose of Section I of this document is to specify the requirements for minimum safe performance of an altimeter system in its normal mode of operation on subsonic aircraft. Compliance with this section is a means of assuring that the altimeter system will satisfactorily perform its intended function when exposed to cinditions encountered in routine aeronautical operations (normal operation)