Mastering the Localizer (and Back Course)

The localizer is a critical component of every Instrument Landing System (ILS) approach, providing the lateral guidance that brings the airplane to the runway. While most pilots are familiar with the basics of flying a localizer, precise tracking takes practice—and the back course variant can be tricky.

Before you dive in, let’s review some essential concepts to sharpen your understanding.

What is a Localizer?

Think of the localizer as an electronic extension of the runway centerline. It provides lateral (left/right) guidance for an ILS approach. The localizer signal is transmitted from an antenna typically located 1,000 feet beyond the far end of the runway, operating on one of 40 reserved frequencies between 108.1 and 111.95 MHz.

The signal is far more precise than a VOR—about four times more sensitive. Full-scale CDI deflection on a localizer typically represents only 5 degrees, which translates to about 350 feet from centerline at the runway threshold. The sensitivity of this guidance makes precise heading control a must.

The localizer antenna is typically located 1,000 feet beyond the far end of the runway.

How to Fly the Localizer

Flying the localizer is all about small, smooth corrections and disciplined heading control:

• Outside the outer marker (typically 4–7 miles out): Limit heading corrections to 5° or less.
• Inside the outer marker: Limit corrections to 2° or less. Use gentle rudder inputs for very fine adjustments.
• Avoid overcorrecting—S-turns across the centerline waste time and add risk during an already busy phase of flight.

Maintaining an exact heading—even in calm air—can be deceptively difficult. Practicing heading discipline during en route legs can pay big dividends when you’re inside the FAF with low visibility ahead.

The Back Course Twist

Some localizers also transmit a signal in the opposite direction, known as the back course. These approaches are less common but still appear in certain parts of the country.

Flying the back course adds complexity due to reverse sensing—where your CDI needle deflects opposite to the aircraft’s actual position. That means:

• When using a traditional CDI, you must fly away from the needle to stay on course.
• Set the OBS to the approach course as a visual reminder, even though it won’t center the needle like a VOR.
• Disregard the glide slope—it’s false information on a back course.
• If using an HSI, set it to the front course of the localizer to eliminate reverse sensing and fly toward the needle as normal.

Mastering back course approaches is an exercise in situational awareness and instrumentation discipline. Pilots who don’t understand reverse sensing can easily find themselves drifting further from the intended path while chasing a misleading CDI.

Flying the back course adds complexity due to reverse sensing—where your CDI needle deflects opposite to the aircraft’s actual position.

Try It Yourself: Interactive Localizer and Back Course Simulators

To help visualize these concepts, we’ve created two interactive simulators that let you drag the aircraft left or right on either a standard localizer or a localizer back course and watch how the CDI responds.

Localizer Instrument Approach Simulator

Back Course Instrument Approach Simulator

Whether you’re new to instrument flying or teaching the next generation of IFR pilots, understanding how to track a localizer—and its more confusing sibling, the back course—is essential. A few minutes with these tools will make the signals click in a way that no textbook can.

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Eric Radtke

It was his first airplane trip at age seven that made Eric decide to become a pilot. "While boarding the airplane, a flight attendant noticed my interest in the flight deck and urged me to go talk to the pilot. I give a lot of credit to that pilot for my career choice." Eric earned a bachelor’s degree in finance and went on to an airline career. He learned to fly at Sporty’s as part of the University of Cincinnati’s Professional Pilot Program, an initiative he later directed.Eric now manages Sporty’s media network including FlightTrainingCentral.com. In addition, Eric serves as a Captain in a Cincinnati-based corporate flight department.

Latest posts by Eric Radtke (see all)

• The Foundation of IFR Flying: Basic Attitude Instrument Skills - August 26, 2025
• Mastering the Localizer (and Back Course) - July 25, 2025
• Instrument Maneuver Spotlight: Non-precision Approach - July 18, 2025