ELECTRONIC AIDS TO AIRCRAFT APPROACH & LANDING

SYSTEMS

ECE 514E-RADAR & SATELLITE ENGINEERING

Wednesday, 16 February 2022

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1. Using Visual Flight Rules (VFR) a pilot to be able to see outside the cockpit, to control the aircraft's attitude, navigate, and avoid obstacles and other aircrafts.

2. VFR flight is not allowed in airspace known as class A, regardless of the meteorological conditions except after failure of two way radio communications.

3. Class A airspace begins at 18,000 feet (5,486m), and extends to an altitude of 60,000 feet (18,288m).

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VISUAL FLIGHT RULES (2)

VISUAL FLIGHT RULES (1)

1. Visual flight rules (VFR) are a set of regulations under which a pilot operates an aircraft in weather conditions generally clear enough to allow the pilot to see where the aircraft is going.

2. VFR applies when the weather is better than basic VFR weather minima, referred to as Visual Meteorological Conditions (VMC).

3. If the weather is below VMC, pilots are required to use instrument flight rules, and operation of the aircraft will primarily be through referencing the instruments rather than visual reference.

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VISUAL FLIGHT RULES (VFR) IN KENYA

1. 500 ft rule: An aircraft must not fly closer than 500 ft to any person, vessel, vehicle, building or structure.

2. 1000 ft rule: If an aircraft is flying over a congested area (town, settlement, etc.) it must fly high enough so that in the case of an engine failure, it is able to land clear without being a danger to people AND it must not fly less than 1000 ft above the highest fixed object within 600m of the aircraft.

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AIRCRAFT LANDING

1. Ability to land an aircraft under conditions of low or zero visibility is one of the most important factors determining the reliability of air travel.

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2. Two Instrument solutions to air travel are:

(a) Ground Controlled Approach (GCA)

(b) Instrument Landing Systems (ILS)

GROUND CONTROLLED APPROACH (GCP)

• Ground Controlled Approach (GCA) is a system for aiding an aircraft during its approach to the landing area.

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The final stages are

by Precision Approach

Radar (PAR)

Initial approach is conducted

with surveillance radar

surveillance radar element

(SRE)

GROUND CONTROLLED APPROACH (GCA) - 2

1. Ground Controlled Approach (GCA) system consists of two radar sets which are usually installed adjacent to the runaway as follows:

(a) Surveillance Radar Element (SRE) is used to control the traffic pattern of the aircraft

(b) Precision Approach Radar (PAR) which is a high resolution short-range set used to conduct actual landing.

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PRECISION APPROACH RADAR

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1. Controllers monitor the PAR displays observe each aircraft's position.

2. They issue instructions to the pilot that keep the aircraft on course and

glide-path during final approach.

3. Precision approach radars are most frequently used at military air traffic

control facilities where the use of general ILS systems will assist the

enemy to locate military target.

THE GLIDE PATH

1. Glide path is path which must be strictly followed by an aircraft up to the touch point on the runaway.

2. The Path is defined for each type of aircraft for a specific airport.

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SURVEILLANCE RADAR ELEMENT (SRE)

1. Surveillance Radar Element (SRE) is used to control the approach of aircrafts and works as follows:

(a) All aircrafts flying within the range of 50 Kms to 80 Kms must be detected

(b) They must be accurately guided to the correct runaway.

2. Detection of the aircraft is made simpler because the flight-path is on a well defined height zone.

3. The detection beam is usually within a maximum angle of 3o to reduce the likelihood of clutter.

4. Moving target Indicator (MTI) radar is used.

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SURVEILLANCE RADAR ELEMENT (SRE) - 2

1. Surveillance radar scans radiation beam continuously over specified volume in space.

2. It determines range, angular position and target velocity.

3. The beam is steered both in azimuth direction and elevation direction in this radar.

4. Can detect aircraft from distance of up to 400 Km.

PRECISION APPROACH RADAR (PAR)

1. Precision Approach Radar (PAR) is used to get more accurate data for landing the aircraft.

2. PAR scans a limited angle in azimuth and elevation about the recommended glide path.

3. It is common practice to use one radar which is continuously switched between the azimuth and elevation aerial systems, the output being switched in synchronism between the bearing and elevation displays as shown in diagrammatic form.

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DOPPLER NAVIGATION

ECE 514E

Wednesday, 16 February 2022

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MEASURING SPEED IN WATER & AIR – THE KNOT

1. A piece of wood was lowered from the back of the ship and allowed to float behind it.

2. The line was allowed to move out freely from the coil as the piece of wood fell behind the ship for a specific amount of time.

3. When the specified time had passed, the line was pulled in and the number of knots on the rope between the ship and the wood were counted.

4. The speed of the ship was said to be the number of knots counted.

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PRINCIPLE OF NAVIGATION DOPPLER RADAR

• Traditionally, a Doppler radar was installed on all aircrafts to give information on velocity with respect to conventional earth coordinates.

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DERIVATION OF AIRCRAFT VELOCITY Vr

1. If the Velocity of the aircraft in the direction of the beam is Vr, and the transmitted frequency is ft, then the frequency of the radar wave at the ground is

2. The reflected wave is received at the aircraft with frequency, fr given by:

3. We can simplify by noting:

4. Therefore

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+=

c

Vff r

tg 1

++=

+

+=

+=

2

221111

c

V

c

Vf

c

V

c

Vf

c

Vff rr

trr

tr

gr

02

2

c

Vr

c

V

c

Vfff rr

ttD

221 =

+−=

ESTABLISHING BEAM CONFIGURATION

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c

VfD

1cos2 =

0=Df

c

VfD

2cos2 =

c

VfD

2cos2 −=

We require more than one beam to obtain the velocity

TWO-BEAM JANUS SYSTEM

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1. Janus System is named after a Greek God who legend has could seek the front and back, i.e has multiple eyes.

2. The 2-beam system may have errors arising from pitching which changes the orientation of the aircraft with respect to the horizontal plane.

3. Also, a lateral velocity of the aircraft causes the Doppler shift of A to increase while that of B decreases.

4. The heading velocity can be obtained from the average of the Doppler shifts between the front and back radars.

5. The lateral drift velocity can be obtained from the difference of the Doppler shifts of the 2 lateral radars.

THREE-BEAM JANUS SYSTEM

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1. In case of pitch angle making the front of the aircraft lower that the rear, the front beam depression angle increases while the rear beam depression angle decreases.

2. This results in an increase in the Doppler shift in the rear and a decrease in the front.

FOUR-BEAM JANUS SYSTEM

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By using a stabilizing antenna, the Doppler shift due to vertical velocity can be made to cancel out.