3. Contents
• What is ILS ?
• Working Principle
• How does ILS Work ?
• Types of ILS
• Advantages of the ILS
• References
4. What is ILS ?
• ILS stands for Instrument Landing System and is a standard
International Civil Aviation Organisation (ICAO) precision landing aid
that is used to provide accurate azimuth and descent guidance signals
for guidance to aircraft for landing on the runway under normal or
adverse weather conditions.
5. Working Principle
• An instrument landing system operates as a ground-based instrument
approach system that provides precision lateral and vertical guidance to
an aircraft approaching and landing on a runway, using a combination of radio
signals and, in many cases, high-intensity lighting arrays to enable a safe landing
during instrument meteorological conditions (IMC), such as low ceilings or
reduced visibility due to fog, rain, or blowing snow.
• An ILS consists of two independent sub-systems. The localizer provides lateral
guidance; the glide slope provides vertical guidance.
6. .
• An ILS Consists of –
1) Localizer:- The primary component of the ILS is the localizer, which provides lateral
guidance. The transmitter and antenna (Shown above) are on the centreline at the
opposite end of the runway from the approach threshold.
7. .
2) Glide Path:- The glide path component of ILS provides vertical guidance to the pilot
during the approach. Glide path is located 750 to 1,250 feet (ft) down the runway from the
threshold (shown above), offset 400 to 600 ft from the runway centre line.
8. .
3) Markers Beacon :- Allow us to establish the distance at which the aeroplane is on the
runway.
(i) 🔵 Outer marker (OM): The outer marker (if installed) is located 3 1/2 to 6 NM from the
threshold within 250 ft of the extended runway centreline to provide the pilot with the
ability to make a positive position fix on the localizer.
(ii) 🟠 Middle Marker (MM): The middle marker ( if installed) is located approximately
0.5 to 0.8 NM from the threshold on the extended runway centerline. The middle marker
crosses the glide slope at approximately 200 to 250 ft above the runway elevation.
(iii) ⚪ Internal marker:
Its placement is more optional, it is at 0.24 miles from the runway and its
colour is white. Its identifier is dots.
9.
10. .
4) DME : Distance Measuring Equipment (DME) is normally collocated with glide path and
provides slant distance to the aircraft with respect to touch down point.
11. .
5) RUNAWAY VISUAL RANGE (RVR) : In order to land, the pilot must be able to see
appropriate visual aids not later than the arrival at the decision height (DH) or the missed
approach point (MAP).
12. .
6) The approach lighting system:-Various runway lighting systems serve as integral
parts of the ILS system to aid the pilot in landing. Any or all of the following
lighting systems may be provided at a given facility: approach light system (ALS),
sequenced flashing light (SFL), touchdown zone lights (TDZ) and centerline lights (CLL-
required for Category II & III operations.)
13.
14. Types of ILS
1
CAT I
Enables aircraft to land in visibility
conditions as low as 1,800 feet (550 m).
2
CAT II
Allows for landing in visibility conditions as low as 1,200
feet (370 m). Requires special pilot certification and
training.
3
CAT III
Enables landing in almost zero visibility
conditions, as low as 50 feet (15 m). Requires
special aircraft equipment, and pilot
proficiency training.
15. Advantages of the ILS
Safety
ILS provides accurate and precise
guidance to the pilot, reducing the
risk of accidents.
Efficiency
ILS enables planes to land in low
visibility conditions, reducing delays
and diversions during inclement
weather.
Flexibility
The ILS can be installed at any
airport, regardless of size or
location, making it accessible to
all aircraft.
