ILS Flashcards
What is ILS?
a precision approach landing radio navigation aid.
It is a short range system which provides lateral and vertical guidance to a runway, allowing aircraft to descend to much lower altitudes on approach during poor weather conditions
5 Principles of the localiser (including band it operates in)
- Located at far end of runway to provide tracking to and beyond runway threshold.
- localiser provides signal which provides instrumentation with lateral guidance allowing aircraft to track extended centreline.
- LOC is tuned using com/nav radio and can be used for tracking on non-precision approach or used with a glide path where glide path and DME are automatically tuned when turning the localiser.
- VHF band 108MHz to 112 MHz with 50 kHz channel spacing
What are the indications in the cockpit regarding the CDI or HSI deviation bar? And what’s course sector and clearance sector?
CDI/HSI each dot represents 0.5º when tuned to ILS localiser.
The area where aircraft receives a CDI bar shift from extended centreline up until the bars at full deflection. Which is a total of 5º wide. 2.5º left & right.
Outside there’s a requirement that CDI bar is held at full scale deflection up until 35º left & right of centreline. If not kept up the signal may be lost and no nav indication can be displayed.
When would a full scale CDI deflection typically occur and what is the length of the total course width at the threshold?
Full scale CDI deflection at 105m from the centreline at the landing threshold.
Total course width 210m at threshold.
What is the localiser coverage?
10º either side of the course along a radius of 25NM from the array.
&
10-35º either side of the course along a radius of 17NM above 2000ft AGL.
Localiser signal characteristics and CDI indications.
Made up of two lobes with a different modulation and transmitted on the same carrier frequency. (Works on the lateral axis) Left amplitude signals at 90Hz (yellow) while right modulates it at 150Hz (blue)
If aircraft moves to either side it receives a stronger modulation and the CDI deflects the course deviation bar
e.g if it moves to the left, it receives a stronger 150Hz modulation and CDI indicates left but commands you to move to the right
Explain localiser back course.
Among the extra lobes radiated from the localiser antennas is a mirror image localiser course extending behind the array, opposite to the course sector
Indications from the back course can be received by aircraft and used to navigate to/from the runway on the opposite side of the array. However, when using the back course, the CDI bar sensing is reversed and there are no glide path indications useable with it
Not in nz
Explain glideslope principles and principle of operation.
The glideslope is the component of the ILS that provides vertical guidance to the pilot.
•Most glideslopes are able to provide guidance to 200 feet above the surface.
The glideslope transmitting antenna is located to the side of the runway approximately 1000ft in from the landing threshold.
PRINCIPLES
The glideslope signal is transmitted on a UHF carrier wave similar to the localiser signal but in a vertical plane.
•The larger upper lobe is a 90 Hz (yellow) signal and the lower lobe is (blue) 150 Hz.
•The signal overlap (1.4º) is calibrated and inclined at a 3º angle to the horizontal.
Explain glideslope angles and indications.
Glideslope angle is typically on a 3º slope (300ft per nm) so:
3000ft above the threshold elevation at approximately 10nm to touchdown.
• 2100ft above the threshold at approximately 7nm.
• 1500ft above the threshold at approximately 5nm.
Indications:
Position of the glideslope relative to the aircraft is indicated by the horizontal glideslope needle moving up and down with 1.4º of movement in total.
Explain marker beacons and indications of passage
A type of VHF beacon position under the extended centreline of the localiser approach course.
Uses a highly directional antenna pointed straight up so that when aircraft passes over it, a signal is received. The signal both illuminates a light and sounds a Morse identifier.
What are the three types of marker beacons and their characteristics.
Outer marker - Identifies Final Approach Fix (FAF) Distance 3.5-6nm before touchdown Low pitch ident (400Hz) of 2 dashes per second Blue light in cockpit
Middle marker -
Typically marks the decision point for a CAT I approach
Approximately 1000m prior to touchdown
Medium pitch ident (1300Hz) of alternate dots and dashes
Amber light in cockpit
Inner Marker
Not always used
Typically marks decision heights for CAT II and III approaches
Distance between 75 and 450m from touchdown
High pitch ident (3000Hz) of 6 dots per second
White light in cockpit
State the localiser and glideslope displacement represented by full scale deviation of the CDI and glideslope indicators.
Localiser max width of 5º
Gide slope 1.4º total
State the rule-of-thumb methods of calculating:
(a) required height above threshold for a 3° glideslope
The approximate correct altitude on a 3° slope can be easily determined by multiplying the distance from the runway (nm) by 300 and adding threshold elevation.
Example: DME 3nm
Threshold = 400ft
3 x 300 + 400 = 1300ft
State the rule-of-thumb methods of calculating: rate of descent required to maintain a 3º glideslope at any given groundspeed.
Groundspeed x 5 = Required ROD
•Example: If an aircraft has a TAS of 140kts and a 20kt headwind component what is the required ROD?
Rate of Descent Calculations
120 x 5 = 600fpm
Glide slope deviation calculation
Your deviation above or below the glideslope in feet can be calculated using the following formulae:
Full Scale Deflection:
nm from touchdown x 70ft = feet above or below
½ Scale Deflection:
nm from touchdown x 35ft = feet above or below
