Mini-X Installation, Setup & User Manual GRT Avionics
Revision A9 88
8.5 Angle of Attack
(not in v32a software)
Angle-of-attack (AOA) refers to the angle of the local airflow relative to the wing. Since the wing will
stall when the “critical” angle of attack is exceeded, AOA is useful for stall warning, and as a means of
establishing an approach speed that accounts for the current weight of the airplane.
The GRT EFIS can display AOA that is derived from either a “calculated” or “measured” source.
The “measured” AOA source refers to use of the GRT AOA option with a dual port pitot probe. This
method uses the two pressures from the pitot probe, and the static pressure, to measure the AOA. This
method provides the most accurate and fastest responding AOA measurement.
Angle-of-Attack can also be calculated by the EFIS by combining a variety of sensor data. AOA calculated
in this manner has the benefit that does not require any dedicated hardware. The drawbacks are that
the calculated AOA is dependent on proper functioning of the pitot/static and pitch attitude data. Also,
the accuracy of the calculated AOA degrades when flying through rising or descending air.
Either type of AOA data may be used to drive two different indicators on the PFD screen.
8.5.1 Approach AOA Indexer
This indicator appears just to the right of the airspeed tape, and shows the angle-of-attack relative to
the optimal for approach. When the angle-of-attack too low (the airplane is flying faster than optimal
approach speed), yellow chevrons pointing up into a yellow circle prompt the pilot to increase back
pressure to reduce speed, and similarly, red chevrons pointing down into a red circle prompt the pilot
to push forward to increase speed. When stall is imminent, the word "PUSH" appears above the AOA
indexer.