EXERCISE WITH FLIGHT SIMULATOR

Through a simulated flight with take off from Rimini airport (LIPR) and

landing at the Bologna airport (LIPE) on a training aircraft Cessna

C172SP Skyhawk, we show the use of the on-board instrumentation for

radio navigation in phases of navigation, airport approach and landing.

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A.D.F. = Automatic Direction Finder

It is a direction finder and it consists of a directive reception system (cardioid

pick-up pattern) that is mounted on a swinging case driven by a motor. It is

automatically directed to a transmitter of known position on the ground

(N.D.B. = Non Directional Beacon).

The instrument provides, referring to the longitudinal axis of the plane, the

direction of the N.D.B. on which it is tuned.

The N.D.B. can officially operate in the frequency band between 200 kHz

and 1750 kHz (normally between 200 kHz and 450 kHz). The ranges are:

navigational N.D.B. : about 280 km

approach N.D.B. : between 45 km and 90 km

The N.D.B. in Italy emit power between 25 W and 300 W.

The A.D.F. does not provide a route but a direction. Because of the speed of

the wind, a plane that always points to an N.D.B. does not travel to the

N.D.B. by a straight line but by a spiral path called “curve of the dog”.

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V.O.R. = VHF Omnidirectional Range

The ground station transmits a radio frequency carrier in the frequency range

between 112 and 118 MHz, modulated by two sinusoidal signals:

- a reference signal with the same phase in all directions;

- a progressively phase-delayed signal with respect to the reference signal

over the whole 360° angle, with direction North - East - South - West.

The match between azimuth degrees and electrical degrees defines 360

standard routes or lines around the V.O.R. station. The V.O.R. is therefore a

radio navigation system with radial position lines.

The on-board V.O.R. receiver, measuring the phase

difference between the two signals, shows,

regardless of the orientation of the aircraft, the

deviation of its position from the defined route and

the direction of approaching or moving away from

the tuned V.O.R. station.

The range of a V.O.R. station generally does not

exceed 200 km. 3

D.M.E. = Distance Measuring Equipment

It consists of a on-board “interrogator” transceiver that emits a steady flow of

radio frequency pulses in random sequence and a “transponder” transceiver on

the ground that receives, amplifies and retransmits the same pulse sequence

(on a different frequency), after introducing a fixed delay t0, together with the

pulses received from all other aircrafts.

The on-board equipment receives all the pulses emitted by the transponder,

recognizes the sequence corresponding to its queries, measures the elapsed

time Δt between the emission of each interrogation pulse and the

corresponding response impulse and calculates from it the distance d between

the aircraft and the D.M.E. station using the formula d = c(Δt/2- t0) (c = radio

waves propagation velocity).

It is therefore a circular position lines system.

The system operates in the frequency band between 960 and 1215 MHz (where

there are 126 channels spaced 1 MHz).

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D.M.E. = Distance Measuring Equipment

The maximum delay that a D.M.E. can measure is conventionally

established to be 2500 μs, which corresponds to a maximum distance of

about 370 km (at the condition that the signal is well received).

The D.M.E. emits, interleaved with the distance responses, the station’s call

sign in Morse code.

The radiated powers vary between a few hundred W to a few hundred kW.

The D.M.E. stations are usually combined with a V.O.R. station in order to

provide the pilot polar coordinates (ρ, θ) of the aircraft with respect to the

V.O.R. – D.M.E. station.

For this reason, the D.M.E. channels were officially matched with the

V.O.R. frequencies.

The accuracy of the D.M.E. is about 50 m.

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I.L.S. = Instrumental Landing System

The ground system, through the on-board equipment, provides the pilot with:

• the indication of the aircraft side displacement with respect to the vertical

plane containing the longitudinal axis of the track, defined by the signal

emitted by a transmitter, called Localizer) in the band between 108 MHz and

112 MHz;

• the vertical displacement indication, with respect to the sloping plane (that is

orthogonal to the above plane and contains the established descend path for the

track), defined by the irradiated signal in the band between 328,6 MHz and

335,4 MHz by a transmitter called Glide path;

• the indication of the crossing of three points of the descent path, placed at 7

km, 1 km and 75 m (optional, less used) from the runway threshold, through

single carrier frequency signals (75 MHz) emitted by three transmitters called

External Marker, Medium Marker and Inner Marker respectively. The first

modulates the carrier with a sine wave at 400 Hz manipulated in Morse code

with uninterrupted lines, the second with a sinusoidal signal at 1300 Hz

manipulated with alternating points and lines and the third with a sinusoidal

signal at 3000 Hz manipulated with uninterrupted points. 6

I.L.S. = Instrumental Landing System

The two planes which form the descent path are generated in the space by

special radiation patterns, within which the carrier is modulated by two signals

at 90 Hz and 150 Hz . The amplitude modulation index of the carrier varies with the distance from the point where the aircraft is in respect with the two

plans. The frequencies of the Localizer and of the Glide path are matched with

each other (40 channels spaced of 50 kHz). I.C.A.O. (International Civil

Aviation Organisation) states that the I.L.S. system must provide a reliable

indication until the aircraft descent to the runway, reaches the following

altitudes:

I.L.S. category I: 60 m

I.L.S. category II: 15 m

I.L.S. category III: 0 m

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G.P.S. = Global Positioning System

The air section consists of satellites deployed in circular orbits in a

configuration that allows you to see, from any point on the Earth’s surface, a

number of satellites between 5 and 8.

The craft in navigation is equipped with a receiver that calculates its position

in the space knowing its distance from at least three satellites; such distances

are obtained by measuring the time taken by the signal emitted by each

satellite to reach the craft and from the ephemeris of each satellite. The

ephemeris are communicated by them to the craft in navigation together with

the informations necessary to synchronize the clock of the receiver with those

on board of the satellites.

The use of the signals from 4 satellites instead of 3 allows you to cancel the

inaccuracies due to the clock of the receiver.

Secondary radar

The system consists of a radar station on the ground that queries the

transponder on board of the aircraft, which in turn transmits to the ground

identification, altitude and other informations, then shown on the radar screen.

The air traffic controller informs the pilot, during take-off, the identification

code that he must set on the transponder (squawk). 8

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Velocity

indicator

Trim

indicator

Altimeter V.O.R. 1

I.L.S.

D.M.E.

indicator

Inclinometer and

virosbandometer

Prow

indicator

(or gyro)

Variometer V.O.R. 2 A.D.F.

Transceiver 1

Transceiver 2

A.D.F. tuner D.M.E.

indicator

Transponder

V.O.R 1 or I.L.S

tuner.

V.O.R 2 tuner

Instruments and radio panel of a Cessna C172SP Skyhawk

Transceiver Transceiver Indicator of prow (or gyro)

Between the waypoints Rimini (LIPR) and Cervia (LIPC) we take the 313

radial of the Rimini V.O.R. : identification RIM frequency 116.20 MHz

Between the waypoints Cervia (LIPC) and Bologna (LIPE) we take the 291

radial of the Bologna V.O.R. : identification BOA frequency 112,20 MHz

Rimini N.D.B. : 335 kHz, Cervia N.D.B.: 387 kHz, Bologna N.D.B. : 413

kHz, Cervia D.M.E.: 113,60 MHz, Bologna I.L.S.(category III): 108,90 MHz

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Since only the runway 12 of the Bologna airport is equipped with I.L.S.

(category III), coming from Rimini need, wanting to use this aid, past the

airport along a downwind arm, turn 90 degrees and still 90 degrees,

approach to the runway 12 and land.

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Web radar

The real-time flights in the skies of Europe:

http://www.flightradar24.com

The real-time flights in the skies of Switzerland:

http://radar.zhaw.ch:80/radar.html

The real-time flights in the skies of U.S.A.:

http://www.passur.com/airportmonitor-locations.htm

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