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How To Fly A Perfect ILS Approach

If you want to fly for the airlines, the ILS will be your new best friend. It's the most commonly used instrument approach in the airline world. Here's how you can fly a perfect ILS approach...

But First... How Does The ILS Work?

Before you get started flying ILS approaches, you should have a little background about how they work. The ILS provides both horizontal and vertical guidance to a landing under instrument conditions, and depending on your airplane's capabilities, you can fly it to nearly zero-zero visibility.

Positioned on the far end of the runway, the localizer transmits signals on 108.1 MHz, up to and including 111.95 MHz (odd tenths only). Localizers have an adjusted course width so that they're 700 feet wide at the runway threshold (full scale fly-left to a full scale fly-right).

Glideslope equipment is usually located 750 to 1250 feet down the runway, and 400 to 600 feet from the side of a runway's centerline. You can usually find the glideslope shed next to the runway's aim point markers.

The glideslope works the same as a localizer, but just turned on its side. The equipment still transmits 90 Hz and 150 Hz lobes, which are interpreted by the ILS receiver. The beam is 1.4 degrees thick, with .7 degrees of glidepath projected on either side of the beam. A typical glideslope will take the airplane down towards the runway at a 3 degree angle.

Want to learn more? Click here to learn everything you need to know about how ILS approaches work.

Set Up And Brief The Approach

As you approach your destination, get the latest weather or ATIS information. ATC will likely announce which approaches are in use. At this point, you may want to begin loading the approach into your FMS or GPS.

Here's How To Brief An Instrument Approach, In 10 Steps

Avoid False Glideslopes

Glideslope signals reflect upward, creating glideslopes, which are often at 6, 9, and 12 degree angles to the runway. This is why pilots are always taught to intercept the glideslope from below, to ensure they don't capture a "false" glideslope.

If it were to actually occur in an airplane, it's difficult to miss the extremely steep descent angle of these false glideslopes.

Flying The 7 Steps Of Every ILS Approach

Unlike non-precision approaches, ILS approaches follow relatively standard profiles. You'll find only minor deviations in glideslope angle (which is usually 3 degrees) and final approach fix intersections across a variety of ILS approaches. You'll most likely be vectored onto the final approach course of an ILS by ATC.

Click Here For The 7 Steps Of Flying An ILS Approach

Calculate Your Three-Degree Glideslope

Groundspeed has a significant effect on descent rate, and there's a formula you can use to ballpark your feet per minute (FPM) descent, even before you get on glideslope. One of the most important parts of instrument flying is getting ahead of the airplane. The following formulas are a great way to do just that.

Option 1... Multiply Your Groundspeed By 5: If you're flying your aircraft on a roughly 3 degree glideslope, try multiplying your groundspeed by 5 to estimate your descent rate. The result will be an FPM value for descent that you should target. As you capture the glideslope, make adjustments as necessary.

Option 2... Divide Groundspeed In Half, Add "0": Divide your groundspeed in half, add a zero to the end, and you'll have an approximate FPM of descent. This is another easy way to target an initial descent rate for a 3-degree precision approach, or even a VFR descent into an airport.

Flying The ILS

To fly an ILS, you first align your aircraft with the runway, using the localizer as guidance. This is typically done by radar vectors from ATC, or with a procedure turn.

You then fly toward the runway and intercept the glideslope from underneath, so you don't intercept a false glideslope. After you intercept the glideslope, you start a gradual descent toward the runway.

There are several different ways that the localizer and glideslope can be represented on flight instruments, but in most glass-panel aircraft, they're represented as a green line or triangle for the localizer, and a green diamond or triangle for the glideslope.

As you intercept the glideslope and start descending toward the runway, localizer/glideslope indications move if you get off course, indicating that you need to fly left/right to stay on course, or increase/decrease descent rate to stay on glideslope. To correct for both, you "fly to the needle".

As you get close to the runway, the localizer and glideslope signals become more sensitive, because the course width of both decreases the closer you get to the runway. Using small corrections, and avoiding "chasing the needle", is essential to fly an ILS all the way to minimums.

How You Can Meet ATP Standards?

Most pilots need to fly an ILS to ACS instrument standards, which you can find here. But if you really want to impress your instructor and fly to FAA ATP PTS Standards, you'll need to:

  • Establish a predetermined rate of descent at the point where the electronic glideslope begins, which approximates that required for the airplane to follow the glideslope. (Hence our rules of thumb in the section above!)
  • Maintain localizer and glide slope within one-quarter-scale deflection.

Are you instrument rated? Do you prefer RNAV LPV approaches over the ILS? Tell us in the comments below.

Swayne Martin

Swayne is an editor at Boldmethod, certified flight instructor, and First Officer for a large regional airline. In addition to multi-engine and instrument ratings, he holds a PIC Type Rating for Cessna Citation Jets (CE-525). He graduated as an aviation major from the University of North Dakota in 2018 and is a former pilot for Mokulele Airlines. He's the author of the articles, quizzes and lists you love to read every week. You can reach Swayne at swayne@boldmethod.com, and follow his flying adventures at http://www.swaynemartin.com.

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