Question of the week: Planned cruise altitude

December 6, 2013

Question: You've plotted a true course of 005 degrees with the intention of cruising at 5,500 feet msl on a VFR flight. You've figured the true airspeed to be 115 knots. The winds aloft at 3,000 feet and 6,000 feet are forecast to be from 260 degrees at 25 knots. The elevation is approximately 900 feet along the entire route. Magnetic variation is 9 degrees east and compass deviation is 0 degrees. What effect do these conditions have on your planned cruise altitude?

Answer: The magnetic course will be in the range between 180, clockwise, through 359 degrees. That means if you want to cruise above 3,000 feet agl, then you should plan on flying at an even thousand foot msl altitude plus 500 feet. According to 14 CFR Part 91.159,  5,500 feet would not be appropriate. Deviations from this rule must be authorized by ATC.