SPEEDS

Calibrated, True and Equivalent Airspeeds, and Mach number

The right portion of the display shows values of SAT & TAT, Altitude, EAS, CAS, TAS and Mach number, and selected altitude and temperature. Change any one of these, and instantaneously see other values updated.

Crossover altitude calculation

The left portion of the display is used for crossover altitude calculation. Dial in the Calibrated Airspeed and Mach number to be used for climb/descent, for which you wish to know the crossover altitude. (When climbing, the altitude above which the primary speed reference usually changes from Calibrated (indicated) Airspeed to Mach number, and CAS/IAS becomes secondary. Conversely, in descents, the altitude below which the primary speed reference normally switches from Mach to CAS. Refer to your aircraftʼs Flight Manual for appropriate climb and descent speeds). Always beware of speed loss during climbs to altitude!

Altitude

Altitude affects the relationship between the various airspeeds, and also the Mach number. Dial in a new altitude, and all the airspeeds (and temperature) will automatically update.

Changing from 1000-foot increments. By default, altitude changes in 1000-foot increments. You can adjust the increment by tapping the altitude thumbwheel. Tap once to switch to 100-foot increments (the thumbwheel appearance will change), once more for 1-foot increments. Tap again to return to the default.

Locking a speed for altitude changes. By default, CAS is “locked” for altitude changes. It will be held constant when you dial in a new altitude, and it is the other speeds that will be recalculated. You can choose to lock EAS, TAS, or Mach number instead. Tap inside any cyan frame to lock that particular speed. A padlock symbol shows which speed is “locked”.

Temperature

SAT, TAT and ISA deviation. The column for temperature shows SAT (static air temperature) and TAT (total air temperature). Deviation from ISA, at the currently selected altitude, in Celsius only, is also displayed. By default, the temperature is set to the ISA temperature for the current altitude.

To find ISA, SAT and TAT at any altitude for the given speeds, simply dial in the altitude.

To change the temperature, tap, or hold down, either the up or down arrow. The airspeeds and ISA deviation values will be updated accordingly.

Note: Temperature (and rise) are exceptionally controlled with arrows, as opposed to a thumbwheel, to optimize the available screen space, particularly on smaller displays.

Temperature rise

The difference between TAT and SAT (the rise), shown in the temperature column, depends on airspeed, but also on the probe used to measure temperature. Specifically the probeʼs recovery coefficient, or Ct. Modern probes usually have a Ct of 1.0, which is the default value used. However, you can adjust the Ct down to 0.7, in increments of 0.01, as appropriate for the probe used in your aircraft.

Tap, or hold down the arrow(s) to adjust Ct.

Auto-crossover mode

When auto-crossover mode is turned on, if altitude is dialed up above the crossover altitude, the Mach number will automatically become “locked”. Similarly, when altitude is dialed down below the crossover altitude, CAS will “lock”.
Enable auto-crossover mode by tapping the button labeled X-OVER. Tap it again to disable auto-crossover.

Conversions

Speeds are shown simultaneously in knots, kilometers per hour, metres per second and (statute) miles per hour. Altitudes are shown in feet and metres. Temperatures in Celsius and Fahrenheit (with some exceptions).

Reset button

Hold the reset button for 3 seconds to return all values to the default settings (sea-level, ISA, 250KCAS, Ct=1.0, crossover 250KCAS / Mach 0.7).


Click here to return to the home page.