Chapter 10

ILS

Instrument Landing System

http://part66school.blogspot.com/2012/08/how-ils-system-work.html

How ILS System works website.

ILS OverviewThe ILS system uses VHF radio (at the airport) to transmit signals that are received by the VOR receiver (in the airplane) and display guidance information on the flight director or send information to the autopilot.

The radio signal that lines up the airplane with the runway is called the Localizer.

The radio signal that keeps the aircraft descending at a safe angle is called the Glideslope.

The Marker Beacon is 3 radio beacons positioned along the extended centerline of the runway that alert the pilot for glideslope intercept, decision height and when to go around.

ILS System Diagram

Localizer Antenna

Textbook page 67 and 70Horizontally focused

Localizer Antenna

Horizontally focused

Glideslope Antenna

Textbook page 67 and 70Vertically focused

ILS CategoriesThere are several categories of ILS, each pertaining to how low the visibility can be in order for the aircraft to land safely.

The categories are based on ceiling and visibility at the airport when the airplane arrives.

Decision Height (DH) Runway Visual Range (RVR).Category I is a DH of 200 feet and an RVR of 2400 feet.Category II is a DH of 100 feet and an RVR of 1200 feetCategory IIIa is a DH of 100 feet and an RVR of 700 feet.Category IIIb is a DH of 100 feet and an RVR of 150 feet.Category IIIc is “0/0”, no visibility, and currently there are no Cat IIIc airports in the US.

The airplane must be equipped and maintained for the various categories and the pilots must also be trained and qualified to land in low visibility conditions.

Runway Lighting

Textbook page 69

ILS Components

The ILS components consist of a Localizer, Glideslope and Marker Beacon System.

These systems have airborne and ground systems.

The compass locator is a low power station picked up by an ADF receiver to guide the airplane arriving from any direction to the outer marker.

Localizer

Left ofcourse

On course Right ofcourse

Textbook page 71

Localizer From the ground, a localizer transmitter projects radio beams aligned with the centerline of the runway.

It operates in the VHF band from 108.1-111.95 MHZ.

The localizer transmits 2 tones: 150Hz and 90Hz, and one tone is on one side of the runway, the other on the other side

The ILS receiver measures the difference of strength of the 2 tones to compute whether or not the aircraft is centered or off course.

Localizer is displayed where VOR is displayed but it is 4x more sensitive.

Textbook page 71

Glideslope

Aboveglidepath

Onglidepath

Belowglidepath

Textbook page 72

Glideslope

The glideslope signal provides vertical guidance.

There are no controls for the pilot to tune the glideslope, it is automatically tuned when he tunes the localizer.

The glideslope operates on the UHF band from 329.15 MHz to 335 MHz.

Just like with the localizer, it transmits 2 tones: 150 or 90Hz to indicate whether the airplane is above or below the glide path.

Textbook page 72

Marker Beacon

Textbook page 75

Marker Beacon

The Marker Beacon receiver is fixed-tuned to 75MHz.

There is a 3-light indicator in the flight deck which will light up the respective light for each marker as the aircraft passes over the marker.

There is also an audio tone which sounds, and the pitch increases and sounds faster as the beacon is approached.

Textbook page 74

Review Q & A Chapter 10 ILS

10.1 Name 3 markers along an ILS.Answer: Outer, Middle and Inner10.2 How is RVR (Runway Visual Range) measured on an ILS runway?Answer: In miles.10.3 Name the Categories of ILS.Answer: I,II, IIIa, b, c10.4 What component of ILS provides an extended centerline of the runway?Answer: Localizer10.5 Name the ILS component that provides vertical guidance to the runway.Answer: Glideslope10.6 How many channels are allocated to localizers?Answer: 4010.7 The localizer frequency is selected on the ______ receiver.Answer: VOR (General Aviation) or VHF Nav (Commercial)10.8 The frequencies of the 2 audio tones that provide left-right guidance on a localizer are ____ and ____.Answer: 90Hz and 150Hz10.9 when a localizer frequency is selected on the VOR receiver, the indicator needle becomes ____times more sensitive than for VOR navigation.Answer: 410.10 The frequencies of the 2 audio tones that provide up-and-down guidance on a glideslope are ____and___.Answer: 90Hz and 150Hz10.11 The compass locator of an ILS is received on the _______.Answer: ADF10.12 How are the glideslope receiver frequencies selected?Answer: Through the VOR or VHF Nav control panel.10.13. What is the frequency for all marker beacon receivers?Answer: 75MHz