Minimum Performance Standards, for Angle of Attack (AOA) and Angle of Sideslip (AOS) Sensors
The new standard will establish minimum performance requirements for angle of attack (AOA) and angle of sideslip (AOS) sensors. The new standard will cover the various sensor technologies used to measure these flow angles and provide an output to the relevant aircraft systems. Equipment such as displays, warning devices, etc. receiving the output from the AOA and AOS sensors will not be covered by this standard.
Rationale: Currently there are no stand-alone minimum performance standards for AOA or AOS sensors.
Today, applicants seeking TSO authorization for their AOA sensors are able to apply for authorization as a part of TSO-C54, the minimum performance standard for stall warning instruments because it contains some requirements for AOA sensors. However this TSO was written in 1961 and is based on SAE AS403 as revised in 1958. The state of the art of AOA sensors and their types of output has significantly changed since 1961. This causes these TSO applicants to request many deviations to TSO-C54 and AS403 thereby essentially creating 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 for the AOA sensors. 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 for AOA sensors 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 consensus was to first focus on developing a stand-alone standard for AOA and AOS sensors. The minimum requirements for these sensors are very similar and easily contained within the same standard. Later AS403 could be revised to include the new AOA standard as a part of the stall warning function.