Altitude Selection

Calculate a suitable cruising altitude by taking into consideration the direction of flight, the weather (winds and ceiling), length of the trip, aircraft performance, and terrain. For our sample flight plan, let’s assume the weather is fine and we are departing at 1700Z. The elevation of the terrain throughout our flight through the valley is a little over 2,000 feet and it’s a relatively short flight so there is no need to climb too high. Therefore, a cruising altitude of 5,500 feet will be fine and will keep us roughly 3,000 above the terrain.

In our case, 5,500 feet is close enough to 6,000 feet so let’s use the forecasted winds at 6,000 feet for our planned departure time of 1700Z. Referring now to the FD below, we can determine that the winds are forecast to be 180° at 25 knots – a headwind for the day’s flight. Do NOT use surface winds from the METAR – they only affect the aircraft for the first few hundred feet. Also, be prepared to interpolate, if needed.

At this point, we are also in a position to take note of our cruise temperature. At 6,000 feet the temperature is -2°C. Assuming a standard lapse rate of -2°/1000 feet, we can estimate the temperature at 5,500 feet to be -1°C. Now we are in a position to fill out the relevant portions of our navigation log as shown below.