Unpacked: Instrument Landing Systems


Welcome to Unpacked, where we demystify hot topics in the airline industry! This time we’re talking about instrument landing systems (ILS).

When you think about how planes take off and land, a couple of factors likely come to mind: pilots and air traffic controllers. Oh yes, and planes. Less obvious, though no less important are instrument landing systems (ILS), or ground to air radio technology that connects pilots and air traffic controllers and helps navigate planes when it comes to landing. These systems have been around for a long time. In fact, ILS is the primary system still in use today that the FAA has classified as a precision approach system.

Image courtesy of Bruce Guenter on Flickr

ILS more specifically provides lateral and vertical guidance for a plane on approach into an airport via a very precise fixed ground-based signal between two antennas, sending a signal to the pilot to aid in landing the plane. This is a very useful piece of technology when we’re looking at low visibility due to fog or other weather. Instrument landing systems also provide tools that help pilots navigate on the ground like in-pavement lighting, touchdown zones lights, runway edge lights and high speed taxi turnoff lights, and transmissometers, which are weather instruments that use lights to measure visibility (try saying “transmissometers five times fast!).

The two ILS antennae are affixed to the runway, one (the localizer antenna) at the opposite end of the runway from where the plane is approaching to provide lateral guidance to help the pilot line up with the center of the runway; the second at the other end, approximately 700 to 1,000 feet down the runway off to one side. The latter is known as a glide slope antenna, which sits facing upward at a three-degree angle in most cases to provide vertical guidance as the flight descends to the runway. The final piece of important technology used to assist with landings is the approach lighting system. These lights are used to guide the aircraft safely to the runway. These lights are usually placed on a series of gradually decreasing towers at the end of a runway, and you’ve probably seen them flashing if you’ve ever driven past an airport late at night.

Flooding at LaGuardia after Hurricane Sandy

There are three types of instrument landing systems currently in place, Category I, II and III. Each type respectively allows the pilot to land in lower visibility. For instance, a Category I instrument landing system can guide a plane about 200 feet from the ground before the pilot needs to see the runway; Category II can guide a plane within 100 feet from the ground; and Category III – the most advanced of the systems – has the precision to safely guide the plane to touchdown on the ground with as little as 600 feet of visibility.

The more precise the system, the more expensive it is to maintain or replace. A Category III system, for instance, is more challenging for airports to obtain and maintain because it’s the most costly of the three. Many smaller airports only provide a Category I system. Also, in order to use Category II and III instrument landing systems, airlines are required to provide additional flight crew training and aircraft equipage requirements. (JetBlue maintains certification for Category III approaches on both our Airbus and Embraer fleets.)

If it’s a sunny day or clear night with high visibility, the ILS isn’t really needed. It’s those rainy, snowy, or foggy, low visibility travel days that make ILS an integral part of operations and missing or broken equipment can mean delays or diversions for flights that then don’t have the navigational aid to land in those less than ideal weather conditions.

LaGuardia flooding the day after Hurricane Sandy

That brings us to Hurricane Sandy, where heavy winds and flood waters damaged the instrument landing equipment at the New York airports, including Newark, LaGuardia and JFK. At LaGuardia in particular, an FAA inspection after the storm revealed that the signal wasn’t taking them to the runway the right way. In fact, they found at the far end of the runway, a pier where the antenna sits had been damaged and was actually moving with the tide. That leaves LaGuardia with one only runway with a fully functional ILS.

The good news is that the Port Authority of New York and New Jersey and the FAA have been on top of addressing and repairing the damage, and we’re looking at most of the technology getting fixed by the end of the year. In the interim, we’re looking at the possibility of delays or diversions in times of low visibility.

The airline industry as a whole has started serious discussions around and plans to upgrade navigational technology to swap the old ILS ground-based technology for new satellite technology (GPS) that a hurricane or any other weather cannot knock out. Known as NextGen, we’re already flying using a new procedure known as RNP to get into the New York airports which allows for more on-time departures and arrivals as we reduce our dependency on ground-based navigation systems. Learn more about our plans with NextGen and our new RNP AR approaches into JFK.

Learn more about the past, present and future of Air Traffic Control

Check out our previous editions of Unpacked and stay tuned for the next up!