How to intercept a VOR radial
Intercepting means joining a given track and then following it. At a VOR that track is a radial. At an NDB the same idea uses QDM for the track to the station and QDR for the bearing away from it. This guide shows how to pick the right method from the angle you still have to close, how to fly the 45 degree intercept and the 90/45 method, and when homing or a DME arc is the better answer.
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WHAT IS AN INTERCEPT?
Your task is to join a given track and then follow it. At a VOR that track is a radial. A radial always points away from the station, so radial 090 lies east of it.
At an NDB the same idea uses different words. QDM is the magnetic track to the station. QDR is the magnetic bearing away from it. QDM and QDR are always 180 degrees apart.
First set your course selector to the track you will fly. Then choose a smart heading that cuts across to reach that track.
PICK YOUR METHOD
Compare where you are with where you want to be. Take the difference between your present radial (or QDR) and the target radial. That difference picks the method:
- Less than 10 degrees: you are almost there. No formal intercept needed, just turn onto the track and correct.
- 10 to 30 degrees: fly a 45 degree intercept.
- 31 to 70 degrees: fly the 90/45 method.
- More than 70 degrees: homing or a DME arc.
You can read your present radial at the bottom of the screen and on the map.
THE 45 DEGREE INTERCEPT
Turn to a heading that cuts the target track at 45 degrees. Hold that heading and wait.
Watch the needle. When the CDI starts moving toward the center, or the ADF needle closes in on the target bearing, you are getting close. Lead the turn a little and roll out on the track course.
A 45 degree cut is comfortable. The needle moves at a pace you can follow, and the final turn is small.
THE 90/45 METHOD
With a big difference (31 to 70 degrees) a 45 degree cut would take very long. So you start with a 90 degree cut instead: turn to a heading perpendicular to the target track and close in quickly.
Keep checking your present radial. When the remaining difference is down to about 30 degrees, shallow out to a 45 degree cut and finish the intercept as usual.
The 90 degree part saves time. The 45 degree part makes joining the track easy and clean.
HOMING OR DME ARC
If the difference is more than 70 degrees, do not chase the track from the side. You have two options.
Homing: turn until the needle points straight ahead and fly directly to the station. While you home, the distance shrinks and the angles change in your favor. When the difference has become small enough, continue with a normal intercept. You can also fly over the station and join the track on the far side.
DME arc: keep your DME distance constant and fly a circle around the station instead. The needle stays roughly on your wingtip. Watch your present radial count toward the target, lead the turn a little, then roll out on the track.
WATCH YOUR DISTANCE
Radials fan out from the station. Close in they are packed tightly, far out they are spread wide. The same 5 degree difference is only a few hundred meters near the station but several miles far away.
So always keep the DME in your scan. The closer you are, the faster the needle moves and the earlier you must lead the final turn.
Be extra careful with a 90 degree cut close to the station. It can push you straight through the track before you can react. When in doubt, use a shallower cut.