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Thread: AF-5500 Calibration upon Startup - What does it do? What about startup on water?

  1. #1

    AF-5500 Calibration upon Startup - What does it do? What about startup on water?

    When turning on the mains the AF-5500 does some kind of internal calibration and the display says not to move the aircraft.

    In our seaplane, we often land on the water and will shut the power down to save battery. It is impossible to have the plane stable while floating in the water. If we land on a beach, the plane may be stable but on a tilt. What are the implications of starting up in these two scenarios? (Unstable floating in waves, stable at a tilt))

    I would assume that we may find the attitude display may show errors in horizon pitch or roll. However that would seem to conflict with the concept of the PTCH ADJ, which would make no sense if the AHRS gets calibrated with every start up of the EFIS.

    If the PTCH ADJ is supposed to fine tune the pitch then what is going on with the start up calibration sequence?

  2. #2
    The startup alignment procedure is to compensate for the solid state gyros' propensity to drift a bit over time. If the aircraft is listing or the water is choppy then it is possible that the AHRS alignment may not complete until after you are airborne, but it will not give you false readings.

    The pitch adjust is to compensate for what you subjectively interpret level to mean, given that all aircraft must vary their pitch to maintain straight and level flight as airspeed changes. The idea, then, is that you use the pitch adjust to make the pitch ladder zero out for straight and level flight at your normal cruise speed, whatever the corresponding AOA.

  3. #3
    Thanks. WITH RESPECT TO, "...AHRS alignment may not complete until after you are airborne, but it will not give you false readings."

    A few follow up questions:

    1. If it will not give false readings without the startup alignment, why bother with the startup alignment? Or does this mean it wont give false readings once the airborne alignment completes?
    2. If the AHRS alignment can be completed while the airplane is airborne and moving, why does the startup alignment warn you not to move the airplane?
    3. Assuming there really is some kind of error if the startup alignment is done when the plane is bouncing on waves or listing on a beach, how would it manifest itself? A tilted horizon in the beginning of the flight until the airborne alignment completes?

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