How Does ILS Work?

An Instrument Landing System (ILS) is a radio navigation system that guides aircraft on approach and landing. It…

How Does ILS Work?

An Instrument Landing System (ILS) is a radio navigation system that guides aircraft on approach and landing. It has been in use since the 1930s, and its operation using directional radio signals remains much the same. Improvements in technology, both on the ground and in aircraft, have improved performance, though, to the point of enabling automatic landings in the worst conditions.

Aircraft are guided on approach using ILS Photo: Vincenzo Pace | Simple Flying

When is ILS used

ILS is a radio navigation system installed at most commercial airports. It is designed to aid pilots in approach and landing, showing whether the aircraft is lined up correctly for the runway. This includes both laterally  (to the left or right of the runway centerline) and vertically (on the correct glideslope for landing). This dual guidance is what is known as a ‘precision approach.’

This can aid pilots on all landings, but especially in poor visibility or night landings. The original intention was to guide pilots down to a minimum height above the runway, from where they would continue landing visually. With improving technology, though, ILS can now take commercial aircraft right down to the runway.

Basic ILS radio operation

ILS works by using two radio signals, sent from transmitters at the airport and received and interpreted onboard the aircraft. One of these, known as the localizer,  will guide the aircraft laterally; the other, known as the glideslope, vertically. They have separate frequencies (for the localizer, it is usually between 108.1 to 111.95 MHz and glideslope higher at 329.15 to 335 MHz).

Each of these transmissions combines two different frequency signals, at 90 Hz and 150 Hz.

ILS operation
Basic ILS operation, using different frequency signals. Image: Fred the Oyster via Wikimedia

The lateral signal is transmitted by the localizer, a physical transmitter placed at the end of the runway. The intersection of the two different frequency signals marks the runway centreline.

And the glideslope signal is transmitted by equipment located to the side of the runway, usually in the area of the runway landing zone. Again this works using the two signals, just vertically this time, with the interaction of the signals marking the ideal glideslope.

Receiving equipment onboard the aircraft will interpret the radio signals (using the relative strength of the signals to determine position).

Correct glideslopes

This signal will follow the established glide path for the airport. For many airports, this is a standard three-degree slope, but some are different. London City Airport, for example, uses a steep 5.5-degree approach on the ILS.

BAe 146 at London City
The ILS at London City Airport will follow a steeper glide path. Photo: James Petts via Flickr

Systems also need to take account of false glideslopes. This can occur when objects on the ground reflect the signal, creating a false glideslope at a steeper angle. These can be avoided by the pilot (and aircraft systems) by intercepting the glideslope correctly and noticing a steeper than anticipated slope.

ILS Categories

ICAO standards (incorporated into practice by aircraft regulators such as the FAA) determine several ILS approach categories. This specifies at what height pilots should switch from ILS to visual guidance (it also specifies minimum levels for visibility).

  • A CAT 1 approach requires the pilot to fly visually after 200 feet above the runway. This is usually used for small general aviation aircraft.
  • CAT 2 approach lowers this minimum height to between 100 and 200 feet.
  • And a CAT 3 approach allows instrument guidance to continue below 100 feet. This can include automatic landing in low visible by the aircraft autopilot.
ILS runway
The ILS categories ate notified on runway markings. Photo: My another account via Wikimedia

Switching to GPS

ILS technology has been around for a long time. Onboard systems and sophistication have, of course, improved, but its basic radio operation remains much the same. The first operational system was used at Berlin Tempelhof airport in 1932 and the US in 1938.

It remains the most common system used today, but there have been (and are) alternatives. Microwave landing systems were introduced from the 1980s, with several advantages, including wider coverage from the airport and better poor weather performance. These have been used at some airports, including London Heathrow, but have not replaced ILS.

Satellite technology and GPS today provide a viable alternative, and several systems have been implemented. GPS-based systems are available in several regions as support for ILS navigation. In the US, for example, there is the Wide Area Augmentation System (WAAS), and Europe has implemented the European Geostationary Navigation Overlay Service (EGNOS).

Navigation and airport ILS is not something we often discuss. Feel free to add any details, or other information about current and future systems, in the comments. 

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JetBlue Flight Landed In Newark With Small Fire

Earlier this month, a Jetblue Airbus A321-200 was seen partially on fire after landing at Newark Liberty International…

JetBlue Flight Landed In Newark With Small Fire

Earlier this month, a Jetblue Airbus A321-200 was seen partially on fire after landing at Newark Liberty International Airport. As a result, the situation is being investigated by the National Transportation Safety Board (NTSB).

The JetBlue A321 unit is still sitting at Newark after 13 days since the incident. Photo: Getty Images

A fiery landing

On July 10th, registration N981JT landed at Newark’s runway 22R after flying in from San Francisco International Airport. However, unusually, a small fire could be spotted on the plane’s right engine cover during its roll out.

According to The Aviation Herald, the A321 then taxied to its gate while maintaining routine communication. The NTSB has since confirmed that a small fire was visible on the engine and the event has been deemed as an official incident, which is presently under investigation. shows that the A231-231 left San Francisco at 22:56 PD to arrive at Newark at 07:23 EDT. The arrival taxi time took 19 minutes following a five hour and 27-minute flight, and the plane hasn’t been in the air since. The aircraft could be seen all over the country in previous days. It had landed at the likes of Los Angeles, Los Vegas, New York JFK, San Diego, West Palm Beach, and Boston the week before 

JetBlue A321
JetBlue’s A321 aircraft have been busy hopping across the United States amid a busy period following a year of significant downturn.

The Aviation Herald’s report comes on the same day we reported on another issue involving a transcontinental flight leaving SFO this month. A United Airlines service heading to Orlando had to be deplaned this week amid a passenger sharing photos with others that were deemed as a “threat”.

More about the aircraft

According to ch-aviation, N981JT, the aircraft involved in the SFO-Newark JetBlue flight arrived at the airline in May 2017. The A321 unit is currently stored at Newark following the fire. It joins one other A321-200 that’s currently on the ground. N957JB is undergoing maintenance. N4048J, an A321-200NX is also presently stored.

Altogether, JetBlue holds 63 A321-200s, 18s A321-200NXs, and two A321-200NXERs in its fleet. The New York-based carrier is a fan of the A320 family and has also been taking on A220 units, which have started to be deployed since April.

JetBlue has been bolstering its fleet ahead of ambitious expansion plans across the US and even the continents. Photo: Getty Images.

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Domestic progress

Most of the airline’s fleet is active following a strong rebound in domestic travel across the United States. Amid this progress, the operator has been heavily promoting travel to and from the New York area. Notably, this summer, it launched an initiative to ramp up summer tourism in New York City, offering special flight deals.

Simple Flying reached out to JetBlue for comment on this incident in Newark. We will update the article with any further announcements from the airline.

What are your thoughts about this JetBlue flight landing at Newark with a fire on its wing? What do you make of this situation? Let us know what you think of the overall incident in the comment section.

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