Training Tip: 40 degrees of separation

November 22, 2013

It’s rewarding to pick out the destination airport from miles away as a cross-country flight nears its conclusion. A bonus is using the remaining time to get the wind direction, pick out the correct runway, and visualize the traffic pattern.

Airports with multiple, long runways that present distinct patterns as viewed from above are ideal for spotting. Take South Dakota’s Aberdeen Regional Airport: its 6,901-foot Runway 13/31, and 5,500-foot Runway 17/35 form an inverted V as depicted on a sectional chart that is oriented with north at the top, where the two runways intersect.

Your preflight planning also produced a cautionary note about those runways when you reviewed the listing for the airport in the airport/facility directory: "Rwy 13 and Rwy 17 apch ends are closely aligned. Verify correct rwy and compass heading prior to dep."

With approximately 40 degrees separating the two runways’ magnetic bearings, that note might strike you as overly cautious. But now, after landing and a quick break, you become momentarily uncertain as you taxi back out over a light surface covering of snow for takeoff on Runway 13.

As usual, your magnetic compass indication sways this way and that during taxi, providing no help, and your directional gyro—ever prone to precession—won’t be trustworthy until the system’s vacuum pump is fully functional, probably after takeoff.

Remember also that at some airports, runway bearings listed as 40 degrees apart may be oriented somewhat more closely. Runway bearings are approximated in 10-degree increments. And, "for a magnetic azimuth ending in the number 5, such as 185, the runway designation could be either 18 or 19," says Section 4-3-6 of the Aeronautical Information Manual.

You wouldn’t want to depart in the wrong direction and pose a collision hazard to area traffic or an aircraft entering a traffic pattern. So stay alert to all airport signs and markings as you taxi out. If your situational awareness is truly top-notch, you will verify preflight research indicating the presence of a visual approach slope indicator (VASI) on the left side of Runway 13. On Runway 17, a precision approach path indicator (PAPI) should be on the right of the runway.

Heed the published cautions about airport hazards and hotspots. Then use all available means to confirm your position for the safest possible departure!

Dan Namowitz

Dan Namowitz | Aviation Writer

Dan Namowitz is an aviation writer and flight instructor. He has been a pilot since 1985 and an instructor since 1990.