Intercepting the localizer at IAD
 

The other day I was flying into iad and told to intercept the localizer close to 30 miles out. I don't fly into there that often. I simply cleaned up the fms, and intercepted in white needles. I figured that intercepting in green would have caused the autopilot to constantly turn back and forth chasing the localizer because we were so far out. My captain told me that technically we have to be in green needles in order to be legal because our instructions were "intercept the localizer." Anyone have any thoughts on the best way to do this next time it comes up with a fed on board?

What runway at KIAD?

It is perfectly legal. If cleared for an instrument approach simply switch to green needles (localizer) when within the localizer service limits. You could even back FMS data up with the localizer in blue needles too. Much more on this, but what you did is appropriate. If not on the visual, definitely go "green" before the FAF.

What's a typical localizer service limit USMC? 20 miles?

The short answer is 18 NM from the antenna, ref AIM chapter 1.

cfibrad is correct - in the US - without an ESV.
As soon as taildragger tells me which runway I will look it up and post it.
ESV's can be extensive if situations are right and there is a need for procedural control out to such a distance. I did a 40 nm localizer approach some time ago at KIAH.

In ORD, they'll ask you to join 40 out.

30nm is a helluva long way out to intercept a LOC. Is it legal? Sure, but it's probably gonna bounce around a bit until you get to 20-25 out.

40?! Holy balls! I hope you're VFR

I've heard that argument at FedEx, too. It makes no sense.

If your aircraft intercepts the LOC, then who cares how it got there. What if you're hand-flying with the flight director off?

Arming NAV, white needles or any other mode and using that to intercept the LOC is transparent to ATC, as long as you end up with the raw data LOC display centered.

Obviously if you were going to have the autopilot track it and intercept G/S, you'll eventually need to enter a mode that actually tracks the ILS.

But, for long distance intercepts of the LOC where signal strength may be low, I don't see the problem.

They meet the same tolerances as they do once they get inside the 18nm SSV. Some localizers bounce around in pretty close. The first time I flew the ILS to 31L at KDAl I thought I was on the ski slopes doing the Giant Slolam! (but it too was within tolerance - but I wonder how a pilot feels the first time going into KDAL IMC and the A/P seems to be chasing its' tail. But then come to think about it - what do you expect with signals bouncing off the downtown skyscrapers?