How to intercept a VOR radial

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.

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.

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.

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.

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.

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.

The intercept angle is a trade. Steep gets you to the radial fast and then asks for a big, well timed turn. Shallow gets you there slowly and rolls out almost established. The angle is the distance you are prepared to fly before you are on it.

Close to the station the radials are narrow and a steep intercept blows through the needle before you can react, so 30 to 45 degrees is the usual answer. A long way out, where one degree is a mile wide, 90 degrees is fine and 45 would take forever. The rule that holds everywhere: the further out you are, the steeper you can afford to be.

Whatever you choose, do the arithmetic before you turn. Radial, plus or minus the angle, is the heading. Saying it out loud catches the sign error, which is the common one.

A VOR needle shows angle, not distance. Full deflection is ten degrees off the selected course, and each dot is two. At 60 miles that ten degrees is ten miles of sky; at six miles it is one. The needle moves ten times faster near the station for the same crosswind and the same heading error.

That is why an intercept that felt lazy at 40 miles feels violent at four. Nothing changed but the geometry. Anticipate it: as the DME winds down, halve your intercept angle and halve your corrections, and lead the turn onto the course by more.

An NDB needle is the opposite kind of instrument. The ADF points at the station and says nothing about a course at all; you build the course in your head from the bearing and your heading. Same intercepts, same angles, more arithmetic.

Homing means pointing the nose at the station and keeping it there. It gets you to the station. In wind it gets you there on a curve, downwind of the radial the whole way, and you arrive from a direction nobody cleared you to arrive from.

Tracking means holding the radial as a line over the ground, with the nose laid off into the wind by whatever it takes. That is the skill every approach and every airway assumes, and it is what the intercept is for: you intercept a radial in order to track it, not merely to reach the beacon at the end.

The tell: on a tracked radial the needle stays centred while the heading sits a few degrees off the course. When homing, the heading keeps creeping and the needle is centred only by accident.

Intercepting a radial outbound is the same manoeuvre with the station behind you, and one trap. The course pointer must be set to the radial you want to fly AWAY from the station on, and the flag must read FROM. Set the reciprocal by mistake and the needle still centres on the radial, but it sends you the wrong way on every correction. That is reverse sensing, and it is the most common intercept error there is.

The habit that prevents it: set the course, look at the flag, say the word. TO for inbound, FROM for outbound. If the flag disagrees with what you intend, the OBS is wrong, not the aeroplane.

Turning early. Watching the needle come alive and turning on the first movement. It comes alive at ten degrees; you want to be turning through the last two or three. Wait for it.

Turning late. The other way round, close to the station, where two dots go by in seconds. Lead the turn by the same rule as everywhere: a steeper intercept needs an earlier turn.

Chasing the needle after roll out. A centred needle that drifts is a wind problem, not a heading problem. Take a drift angle, hold it, and let the needle settle before you change it.

Forgetting the flag. See above. It is the difference between an intercept and a slow drift away from the radial with the needle centred.