Minimum Performance Standard Angle of Attack Equipment
This SAE Aerospace Standard (AS) establishes the minimum performance requirements for an angle of attack (AOA) system. This document covers two basic AOA Systems. One measures airflow and pressure distribution on the airfoil, and the other measures the angle of airflow with respect to an arbitrary reference line. Each type of system includes, as a minimum, a sensor and a display to the pilot representative of the aircraft's AOA.
Rationale: TSO-C54 is the minimum performance standard for stall warning instruments. This TSO was written in 1961 and is based on SAE AS403 as revised in 1958. Stall warning is now a system function not envisioned at that time. An important component of a stall warning system is the angle of attack (AOA) measuring instrument. The state of the art of AOA instruments and their types of output has significantly changed since 1961.
Today, TSO applicants request many deviations to the TSO-C54 and AS403 thereby creating essentially an entirely new specification each time. The FAA’s concern with this situation is whether or not the original level of safety may be compromised.
Another important concern with TSO-C54 and AS403 are the anti-icing and de-icing requirements. AS403 does not take into account the current body of knowledge on atmospheric icing and does not provide the required performance level of safety in many applications.
The FAA would like to have more meaningful minimum performance requirements so fewer deviations taken to the minimum performance standard in the TSO. The FAA is open to the idea of separating the stall warning system requirements from the AOA sensor requirements.
The A-4ADWG committee and the FAA have discussed alternatives and the consensuses was to first focus on revising AS8046 to become a stand-alone standard for the AOA sensor and then revise AS403 to handle the stall warning function. These activities may eventually overlap to some extent.