Maintain the published track and you’ll stay on the localizer.
Sounds simple. Makes sense. But it’s not instinctive. You have to think about it.
Here’s a thought experiment. You are running a train down a straight track. You can’t see outside. You have a stopwatch,
Simple, right? You accelerate to 60 mph, hit the paintgun remote and the stopwatch at the same time. Exactly 60 seconds later you hit the paintgun remote again. Mission accomplished!
But what if you are flying an airplane doing 120 knots? You are on (over) the track and you hit the paintgun. You wait 30 seconds and hit it again. Where is the second blob of paint? Sure, it's 1 nautical mile ahead, but is it on the track?
Yes, if your track hasn't changed. That's easy for a train but a big IF for an airplane. The wind could change. Your heading could change. Then the second blob of paint will not be on the track. It will be off to one side. Your localizer needle will be off to one side.
In math this is an example of integration. You are adding up what happens to your position as a result of your velocity vector. The INS or IRS in an airliner does it. Experienced pilots do something like it in their heads.
If you have a Garmin 430 in your airplane you can go to NAV page 1 and fly so TRK is the same as DTK. If you don't you'll have to do it the old-fashioned way, flying heading to compensate for drift. Either way, try to have the picture in your head.
We'll speak more about integration in future blogs. It's a great help if you want to fly IFR with precision.