Air Data Faulty
- Matt Skelton
What triggered the failsafe?
Good airspeed readings are required for safe and stable flight. Â The airspeed failsafe is used when the autopilot determines that the airspeed information it is receiving from the sensor is not valid. This can happen for a few reasons:
Cause | Info |
|---|---|
Leaks | The PHX air data system uses a series of tubes, hoses, and an airspeed (pressure) sensor. In nominal conditions the combination of tubes, hoses, and the sensor are open on one end and tightly sealed along the length to the airspeed sensor. This allows for accurate pressure readings by the sensor. If any of the interconnects or hoses are damaged or leak pressure between the open end of the system and the airspeed sensor, the airspeed reading will not be correct. |
Clogs | The airspeed reading will be incorrect if the open ends of the system are clogged. This does not allow for pressure changes to be detected by the airspeed sensor, thus giving an incorrect airspeed reading. |
Wind | The PHX tries to determine wind direction by measure forces in flight. During the early phases of the mission the aircraft is still trying to determine the wind direction and may not yet have a good estimate. Sometimes this estimate is off enough to disagree with the airspeed that is being reported by the sensor and can trigger a false positive for the failsafe. If this occurs the user should check the Pitot tube after landing to verify that it is in good working condition. |
What will the aircraft do?
The aircraft will continue flying the mission in No Airspeed Mode. In this flight mode the aircraft will attempt to maintain a pre-determined throttle setting that is intended to keep the aircraft flying at a safe airspeed in nominal conditions (Midwestern density altitude @ 70F). This mode may have marginal performance when operating outside of nominal conditions. Such as, flying in high temperatures or in areas with a density altitude greater than 1000ft MSL. This flight mode is less efficient and the battery will deplete faster than normal.
In the case of a false positive the aircraft may determine that the airspeed readings are valid after a few minutes and will resume using air data while flying.Â
What should the pilot do?
The pilot should visually find the aircraft in the sky and verify that the aircraft is flying as expected. After there is visual confirmation the best practice is to use the RTL function and get the aircraft safely back on the ground. Then inspect the air data system for damage.
The pilot may choose to continue flying the mission after visual confirmation. In this case the pilot should continue to watch the aircraft while it is flying and use the RTL function if any abnormalities, wing wobbles, or nose dips are observed. Ground speed readings should also be monitored to sanity check that the aircraft is moving at roughly 35mph relative to the wind direction.Â