Aerodromes

5.1 Introduction [S]

A plane should be in the air and not on the ground, but eventually they all come down – preferably at an airport. 
Hence it’s important for an air traffic controller to have good knowledge about how the airport is built. 
All airports are built on the same principal, regardless of size. Take a closer look at the chart below and study the design.

 

5.2 Runway designators (numbers) [S]

A runway is a strip used for take-off and landing. 

The runways are numbered according to the compass-direction they are headed, rounded off to the closest tenth degrees. A runway that has the “course” 180 degrees is hence named 18 and one with ”course” 154 is named 15. Since you can use a runway from both directions, it’s named with the contra-course from the other side (18/36). 
Some airports have parallel runways, i.e. more then one runway that has the same number. They are named with the suffixes R (right), and L (left) after the number to tell them apart if they are two and R, C (centre) and L if there are three. 
There are two pairs of numbers that aren’t used in some countries; 02/20 and 13/31, even though the runway might have those headings. The reason for this is the risk for mix-up if the figures are reversed. 


5.3 Traffic Circuit [S+]

The traffic circuit is a race-track around the airport where every side has its own name. If a plane is doing a instrument-guided approach to the airport, the traffic circuit isn’t used. But for visusal approaches some parts or the whole pattern is used. The traffic circuit usually goes anti-clock-wise, called left-(hand)-traffic-pattern/circuit. At some airports it’s the other way (right-hand), in those instances this has to be clearly stated by ATC.


 

5.4 Chart over typical airport [S]



 

5.5 Instrument Landing System ILS [C]

Instrument Landing System (ILS) operates between 108 and 111.95 MHz, on odd tens. So 108.20 MHz must be a VOR frequency, and 108.10 can be an ILS frequency. 
The system consists of three elements; Localizer, glide path and marker beacons. 

 

5.5.1 Localizer [C]


Localizer gives information about the lateral navigation, and will guide the pilot straight ahead on the final approach course towards the runway. 
Basically it transmits a 90 Hz signal on one side (left side of runway) and a 150 Hz on the other side (right side) of the runway. 
If the instrument in the aircraft senses a stronger 150 Hz signal, it will deflect to the left, and visa versa with 90 Hz. 
If the instrument senses equal 90 Hz and 150 Hz signal, the needle is in the middle position, and the aircraft is centred on the extended centreline. 
The localizer signal is usually accurate till 25 nm out.

 

5.5.2 Glide path [C] 

Glide path operates between 328.6 till 335 MHz. Again a 90 Hz and a 150 Hz signal is generated. 90 Hz is above the glide path, 150 Hz is below. 
The glide path angle may vary, but is generally between 2.5 and 3.5 degrees (3 degrees is common). This angle is chosen so that airliners can make a smooth stabilized approach and not have to dive down with high rate of descend. Standard is 300 ft per nm. 
Again the Glide path frequencies are coupled to the Localizer frequencies.

 

5.5.3 Marker Beacons [C]

Marker beacons operate on a fixed frequency of 75 MHz. The purpose is to have a fixed altitude/distance check on the ILS. It is a beacon which transmits straight up. 
The Outer Marker (OM) is usually around 4 nm out on final, and should therefore be passed at (4 x 300 ft) 1200 ft AGL. The Outer Marker has a 400 Hz signal which triggers a blue flashing light in the cockpit, together with a dah-dah-dah audible tone.
Some ILS's have also a Middle Marker (MM). It is positioned 1/2 nm in front of the runway, and has a 1300 Hz signal. It triggers a yellow light in the cockpit, together with a dah-dit-dah audible tone.

 

5.5.4 ILS Classification [C]

ILS Classification is used to determine the accuracy of the landing system. 
Category one (CAT I) is the least accurate, and CAT III is the best. This means you can fly the approach to lower limits (decision heights) on a CAT III ILS than on a CAT I ILS. 
When you reach the appropriate limit you need to see the runway, otherwise you have to go around and fly the missed approach procedure. We are only talking about the ground facilities here. In real life there are more factors which can change your lowest limit.
  1. Pilot qualification
  2. Airplane qualification
  3. Ground facility qualification

Categories of precision approach and landing operations: 
          (As specified in ICAO EUR Doc 013, second edition April 2005) 
          http://www.paris.icao.int/documents/pdf/eur_doc013_2ed_en.pdf

Category I (CAT I):
Decision height not lower than 60 m (200 ft) and with either a visibility not less than 800 m or a runway visual range not less than 550 m.

Category II (CAT II):
Decision height lower than 60 m (200 ft), but not lower than 30 m (100 ft), and a runway visual range not less than 350 m.

Category IIIA (CAT IIIA):
a) a decision height lower than 30 m (100 ft) or no decision height; and
b) a runway visual range not less than 200 m.

Category IIIB (CAT IIIB):
a) a decision height lower than 15 m (50 ft) or no decision height; and
b) a runway visual range less than 200 m but not less than 50 m.

Category IIIC (CAT IIIC):
No decision height and no runway visual range limitations.

An airport needs to meat several requirements before it can be approved for the higher CAT-procedures. We will not go into detail regarding these requirements.
If the weather minima for CAT I isn’t fulfilled the airport has to reorganize into “low visibility procedures”. This has effect on the whole airport and uses more resources. Many of these changes don’t affect us in the virtual world, but some do and are described in the GUIDE. If “low visibility operation” are in use CAT II holding point should be used instead of CAT I holding point.
 
If the airport isn’t approved for higher approach categories it has to close. Traffic will then be diverted to other airports.
 
Note.— Where decision height (DH) and runway visual range (RVR) fall into different categories of operation, the instrument approach and landing operation would be conducted in accordance with the requirements of the most demanding category (e.g. an operation with a DH in the range of CAT IIIA but with an RVR in the range of CAT IIIB would be considered a CAT IIIB operation or an operation with a DH in the range of CAT II but with an RVR in the range of CAT I would be considered a CAT II operation).
 
 

5.6 Available runway length [C+]

The length of the runway is very important when determining if it enough to land and start from. Different airplanes require different length of runway in order to land and take off. This is of course affected by the weight of the aircraft, but also by weather-conditions. The pilot must make sure that the available runway-length is sufficient and the ATC should have knowledge as to what the abbreviations mean and where the information can be found, if needed.
 
The ICAO requires that the first four of the following full runway declared distances be calculated and promulgated for each runway intended to be used by aircraft operators engaged in international commercial air transport:

  1. Take-off run available (TORA)
    The runway length declared available and suitable for the ground run of an airplane taking off.
  2. Take-off distance available (TODA)
    The TORA plus the length of any remaining runway or clearway beyond the end of the TORA. The usable TODA length is aircraft performance dependent and, as such, must be determined by the aircraft operator before each takeoff.
  3. Accelerate stop distance available (ASDA)
    The runway plus stop way length declared available and suitable for the acceleration and deceleration of an airplane aborting a takeoff.
  4. Landing distance available (LDA)
    The runway length declared available and suitable for a landing airplane.
  5. Clearway: 
    A defined plane extending from the end of the runway with an upward slope not exceeding 1.25 percent, above which neither object nor any terrain protrudes. The ability to use a clearway in runway length calculations is dependent on air carrier policy.
  6. Stopway: 
    A defined rectangular surface beyond the end of a runway prepared or suitable for use in lieu of runway to support an airplane, without causing structural damage to the airplane, during an aborted takeoff.

 

5.7 Lights [C]

An airport may look like an over-decorated Christmas-tree during night with all its different lights of different colours. Since we can’t control the lights in our virtual environment, (at least yet) it will only be covered briefly. 
The lightning-system should be turned on when:
  • During darkness, or when the centre of the sun-disc is more then 6° under the horizon.
  • During daylight, if the visibility and/or cloud-base is under certain minimums.
  • On the request from an aircraft.

 

5.7.1 PAPI – Precision Approach Path Indicator [C]

PAPI is a light system positioned beside the runway that consists of two, three, or four boxes of lights that provide a visual indication of an airplane's position on the glidepath for the associated runway. 
Each box of lights is equipped with an optical apparatus that splits light output into two segments, red and white. 
Depending on the angle of approach, the lights will appear either red of white to the pilot. 
Ideally the total of lights will change from white to half red, moving in succession from right to left side. 
The pilot will have reached the normal glidepath (usually 3 degrees) when there is an even split in red and white lights. 
If an airplane is beneath the glidepath, red lights will outnumber white; if an airplane is above the glidepath, more white lights are visible. 

 

5.7.2 Runway Lights [C]

Runway Edge Lights are used to outline the edges of runways during periods of darkness or restricted visibility conditions. There are also runway centre lights. 
These light systems are classified according to the intensity they are capable of producing; High Intensity Runway Lights (LIH or HIRL), Medium Intensity Runway Lights (MIRL) and Low Intensity Runway Lights (LIL or LIRL). 
The HIRL and MIRL systems have variable intensity controls, wheras the LIRL normally have only one setting. The controller in the tower alters the intensity depending on the weather and pilots requests. 
Runway edge lights are white. 
Lights marking the ends of the runway emit red light toward the runway to indicate the end of the runway to a departing aircraft and emit green outward from the active runway to indicate the threshold to landing aircrafts. 

 

5.7.3 Taxiway Lights [C+]

Generally taxiways are marked with yellow lines (or sometimes white). A continuous yellow line marks the centerline of the taxiway. Taxiway edges are usually marked with doubble parallel yellow (or white) lines.
For night operations, taxiways are usually edged with blue lights, to distinguish them from the white lights of a runway. Larger airports sometimes add additional green centerline lighting. The centerline lighting is embedded in the taxiway, and an aircraft landing gear can thus roll over the lights.
The taxiway ids are shown on black and yellow signboards along the taxiway that are lit during darkness. 

 

5.8 Areas of interest [S+]

The airport is divided in different areas with different names in order to create a system that is similar on all airports.
Different rules apply for the different areas, hence the importance to have knowledge about them. 
 
 

5.8.1 Movement area [S+]

These are the areas on which aircraft can be moved around, are named. This includes the runway, taxiways, apron and other areas intended for aircraft and maintenance vehicles. 

 

5.8.2 Manoeuvring Area  [S+]

This is the part of the airport that is used for start, landing and taxiing. 
In most countries, this is the only area where you need a clearance before you are allowed to move the aircraft.


5.8.3 Runway  [S+]

This is the area intended for take-off and landing. 
Note that inactive runways i.e. those that are not used with a certain runway configuration also are to be considered a runway for the purpose of clearance. 
All movement on runways need clearance – whether it is active or not.

 

5.9 ICAO and Airport names [S+]

ICAO was founded in 1944 and is since 1947 a UN organization. 
ICAO stands for International Civil Aviation Organization. 
ICAO mission is to make flying safer. Its work is regulated by the Chicago convention. 
ICAO has introduced a 4 letter naming system for all airports worldwide. 
The first letter is the ICAO region. The second is the country, the third the FIR and the fourth the city or airport. 
There are of course exceptions to this rule; KJFK (John F Kennedy) is one.

Example: 
EDDF: E=Northern Europe, D=Germany, D=International airport, F=Frankfurt
LFPG: L=Southern Europe, F=France, P=Paris, G=de Gaulle.