Instrument Flying: Behind the Basics – 3


We’ll start with a new image today – the megaphone. Put the small end at the touchdown point, line it up with the runway, and tilt it up three degrees. This is the ILS, or at least a useful image of it.

The picture helps because it gives an instinctive feeling for what we have to do to fly an ILS:

  • Maneuver into the big end of the cone
  • Fly down its axis
  • Make smaller corrections as we get closer to the runway

Last time we talked about how to stay on the localizer – maintain the published track – and how we were using integration. Looking closer, we can take the integration back several levels:

Bank --> Heading Change (and thus Track Change) --> Lateral Displacement

A shallow turn for a short time means a small heading change, changing the track. Imagine the new track drawing an arrow – this is your velocity vector. The longer you stay on the track, the longer the arrow. Visualize (I'll add diagrams when I learn the software) the arrow: if you are correcting back to the on-course you'll want to return to your tracking heading when the tip of the arrow gets there.

The same method – integrate and visualize – works for the vertical axis:

Power + Pitch --> Vertical Speed

Use V/S as you would track to manage vertical displacement – to track the glideslope, if you will. The same method works in both axes:

  • Before you start the approach, have targets in mind – the published track,  and a target vertical speed you calculate from your planned airspeed on approach: airspeed/2 X 10 = 600 fpm for 120 knots (if you have GPS, use your groundspeed).
  • Fly into the big end of the cone and center the localizer.
  • Fly the target heading and see what happens. Now you know something about the wind. Adjust your target. (If you have GPS, flying the published track will keep you on the localizer.)
  • Correct back on, then fly the new target. Repeat and get it nailed (at least for this altitude).
  • As the glideslope comes down to meet you, do what you need to get your target V/S. (It should be as little as possible and preferably only one thing: reduce RPM or MP a certain amount; put the gear down.)
  • See what happens. Adjust your target. (If you have GPS, glance at the groundspeed. If it's only 100 knots, your new target is 500 fpm.)
  • Correct back onto the glideslope by adjusting V/S, visualizing the arrow (your velocity vector in the vertical axis) intercepting the G/S. When you're back on, fly the new target.
  • Continue as above, visualizing the megaphone as it gets smaller, guiding you to that window 200 feet above the approach lights. (Your corrections are getting smaller and smaller.)
  • KEEP YOUR TARGETS IN YOUR HEAD RIGHT DOWN TO MINIMUMS. (They are now accurate to a degree or two of heading and 50-100 fpm.)

That's it! Simple, right?

Actually, it is, and it works, but it does take some thinking about. For example: if the needles are centered, are you flying down the axis of the megaphone?

We'll look at that next time.