Garmin GPS 155XL Pilot's Manual & Reference

Also see for GPS 155XL: Maintenance manual Installation manual Installation manual

23SECTION1The density altitude/true airspeed function is also accessed from NAV Menu 1.Density altitude is the theoretical altitude at which your aircraft will perform dependingon several environmental conditions, including air pressure and total air temperature(the temperature including the heating effect of speed, read on a standard outside tem-perature gauge on most aircraft). True airspeed considers the same factors.To calculate the density altitude and true air speed:1. Press N and rotate O until NAV Menu 1 is displayed.2. Press C and rotate O to highlight ‘Dalt/tas?’.3. Press E to access the density altitude page.4. Use K and O to enter the indicated altitude (‘ialt’) and press E.5. Use K and O to enter the calibrated airspeed (‘cas’). Press E.6. Use K and O to enter the air pressure (‘pres’) and press E.7. Use K and O to enter the total air temperature (‘tat’).8. Press E and the density altitude and true airspeed will be calculated and displayed.9. Press C to remove the cursor.If your installation includes components to provide any of the informationrequired on the density altitude page, they will be used as the defaults.The f uel planning page will display fuel requirements for both direct-to naviga-tion and programmed routes. The fuel planning function requires the pilot to enterthe initial amount of fuel on board and the flow rate. You may also enter differentground speeds to view information based on different travel times. If your installationis interfaced to a fuel flow sensor, the flow rate and other information will be sup-plied by the fuel flow sensor, and need not be entered manually.Fuel planning page showing calculation from pre-sent position to ‘KDAL’.Density altitude/true airspeed pageNAV KEYDensity Altitude &True Airspeed