ILS was introduced back in the 1930s and remains one of the most accurate forms of approach navigational aids for pilots. The radio navigation system allows safe descent by directing the plane down a slope to the touch town position on the runway.

Multiple radio broadcasts provide a precise landing approach with horizontal and vertical aerial guidance a few meters before touchdown using the ILS. The guidance can be so precise that pilots can land at the aerodrome without seeing the runway when this system is used.

Given the importance of the Instrument Landing System in enhancing safety during poor weather conditions, instructors at Momentum Flight Training have shared some important concepts as a refresher, enabling you to gain an edge as you transition to your new role as a first officer in regional airlines.

Our 1-day, 3-day, and 5-day aircraft simulator training programs are based on in-class knowledge and practice in AATD simulators. They help pilots familiarize themselves with the systems and mechanisms of the aviator they'll be flying.

While all our programs have up-to-date curriculums and adhere to all FAA regulations, you can speak to our instructors to tailor your learning experience according to the unique specifications of your chosen regional airline.

What is an Instrument Landing System?

An ILS comprises two signals: the one for vertical guidance is called the glide path or glideslope and can be found in the header of the runway. Meanwhile, the horizontal one, located around 300 meters from the runway, is known as a localizer and guides pilots along the center line of the runway. Since the ILS provides both vertical and lateral guidance, it's also considered a precision approach.

Components and Operations of an Instrument Landing System

Localizer

LLZ refers to a VHF transmitted at odd frequencies in the lower VOR frequency range, between 108 MHz and 111 MHz. A horizontally polarized antenna structure generates two modulated signals past the far end of the runway. A 1,500-foot field is built five miles from the approach runway. The field tapers to the width of the runway adjacent to the landing threshold.

A VHF carrier wave with a 150 MHz modulated signal fills the approach area's right part, whereas a 90 Hz signal can be found on the left side. This VHF frequency on the localizer, found on circulated aviation charts and approach plates, turns into the VOR receiver of the aircraft.

The receiver utilizes localizer components and circuitry common to both, while the circuitry of the regular VOR reception is switched off. The received signals are rectified and filtered into DC before they can be used to drive the CDI.

The Course Deviation Indicator of the ILS or VOR displays swerves to the left when the aviator gets a 150 Hz signal. The symbol implies that the runway is to the left. The pilots must correct their course with a left turn to align the CDI on the display as well as the aviator with the centerline on the runway. The pilot should turn to the right when the VOR receives a 90 Hz signal in this situation.

Glideslope

The ILS' glideslope provides the vertical direction required for a plane to descend for the landing stage. The aircraft gets funneled down the touchdown location of the runway at a three-degree angle because of radio signals.

The broadcasting glideslope antenna is nearly 1000 feet away from the threshold, off to the approach runway's side. A wedge-like pattern is transmitted, and the field narrows as it reaches the runway.  

This transmitter glideslope antenna is horizontally polarized, with a frequency range between 329 MHz and 335 MHz in ultra-high frequency, which is then matched to the ILS’ localizer frequency.

When the ILS or VOR receiver is set for the approach, the glideslope receiver gets tuned automatically. It also sends out two signals, 150 Hz and 90 Hz. These signals are decoded in the same way as the localizer receiver.

It controls the vertical course deviation indicator or the glideslope indicator, but at a 90-degree angle. The ILS or VOR localizer glideslope and CDI are displayed together, regardless of the type of instrumentation in an aviator.

Compass Locators

Pilots must be able to intercept the ILS to be able to use it. And compass locators are transmitters that are designed to help pilots achieve this. The first is typically found at the outer marker beacon around four to seven miles from the runway threshold. The second can be found in the middle marker beacon, about 3500 feet from the runway threshold.

The outer marker compass locator is a 25-watt non-directional beacon with a range of nearly fifteen miles. Omnidirectional LF radio waves are sent out that are keyed with the first two letters of the instrument landing system. Since the locator is intercepted with the ADF receiver, no other equipment is needed.

But if the middle marker compass locator is used, the functionality is analogous, but it will be signified as the last two letters of the ILS identifier. The pilot will direct the airplane to glide down the path to the runway once it is spotted.

Marker Beacons

These radio transmitters send out signals showing where the aviator is on the glide path approaching the runway. A 75 MHz carrier wave with a 400 Hz audio tone modulation is emitted in a succession of dashes in an incredibly straight and thin transmission.

A blue light gets illuminated on the instrument panel when the marker beacon receiver receives the signal. This, along with the localizer, oral tone, and the glideslope indicator, helps the plane to be located on an approach positively.

Meanwhile, the middle marker beacon broadcasting at a 75 MHz frequency and located approximately 3500 feet from the approach runway is modulated with a 1300 Hz, a series of dashed and dots to avoid confusion. An amber-colored light illuminates the instrument panel when it receives the signal.

In some instrument landing System approaches, an inner marker beacon is used where signals modulated at 3000 Hz in dots are emitted. It's near the land-or-go-around and threshold of the runway approach. A white light is illuminated on the instrument panel when the signal is received.

However, marker beacons are now largely obsolete because the latest ILS have DME (Distance Measuring Equipment) to calculate the distance accurately. With the advent of new technologies, pilots have many options when it comes to landing and taking off safely or finding their way from above.

Learn all about them and a lot more in 1-day, 3-day, and 5-day aviation pilot program classes offered exclusively at Momentum Flight Training.

All three advanced flight training programs are targeted at improving the skills and proficiency of aspiring regional pilots. You get the chance of familiarizing yourself with the aircraft that you'll be flying as first officers in the regional airlines.

The combination of our in-class lectures and sessions in simulators that replicate the systems in the bombardier crj 700 american airlines, 550, 700, and 900 enables pilots to comprehend mechanisms and navigate diverse flight situations confidently.

Call [833] 427-5876 for more information on our tailored programs aimed at helping aspiring pilots move upward and beyond the regional airlines.