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6.75 RVSM. In order to make more FLs available to turbojet traffic in the cruise, a system has been adopted which prohibits VFR flight (thus making VFR levels available to IFR traffic). In order to achieve this, the separation between IFR levels between FL290 and FL410 inclusive is reduced from 2000 ft to 1000 ft. It is a requirement of aircraft using the RVSM system that they be fitted with A/TCAS and be approved by the airspace authority. Above FL410 the altimeter errors are considered too great to continue the 1000 ft separation.
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Figure 6.14 Reduced vertical separation minima
Special VFR
6.76History. With the introduction of airspace restrictions in the late 1960s, military aerodromes close to large international aerodromes, specifically Northolt in proximity to the rapidly expanding Heathrow, found that IFR procedures were mandatory in the new control zones when previously VFR procedures were generally accepted. In order to allow aeroplanes to fly into and out of Northolt (in the then Heathrow Special Rules Zone) a procedure based on a corridor in which visual navigation was required was set up. Providing the pilot could see the ground, he could navigate and provided he remained clear of cloud he could avoid collisions. A system of ‘not quite’ IMC or special VFR was invented. Until the late 1970s this was applied in what was known as the Northolt special VFR corridor. It was expanded to include the general aviation aerodrome at Denham and its advantages for aeroplanes and pilots unable to comply with IFR were obvious. When the classes of airspace (A - G) were introduced, ICAO also adopted the special VFR as a procedure with appropriate international amendments.
6.77SVFR. SVFR is defined by ICAO as a VFR flight cleared by ATC to operate within a CTR in meteorological conditions below VMC. It is only applicable to flights into, out of, or within a CTR. ICAO requires that the ground visibility within the CTR is not less than 1500 m before a SVFR flight is permitted to enter the CTR to land, take off and depart, cross or operate locally within the CTR. More restrictively, JAR OPS-1 requires 3000 m visibility for a SVFR flight to be commenced.
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Distress and Urgency Signals
6.78 Distress: Definition - An aircraft (or vessel) is in grave and imminent danger and requests immediate assistance.
• A distress message is preceded by the word MAYDAY repeated 3 times.
• Visual signals from an aircraft in distress may include
• A succession of RED pyrotechnics
• A RED parachute flare
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6.79Urgency. Definition - An aircraft has an urgent message to transmit concerning the safety of a ship, aircraft, vehicle or other property of a person on board or within sight. An urgency message is preceded by the words PAN PAN repeated 3 times.
6.80Non-emergency Situation. If an aircraft has a communications failure or a malfunction that makes it imperative that the aircraft is landed but the pilot does not require any other assistance, the pilot shall indicate the fact by repeatedly switching the landing lights (or any other light) on and off.
6.81SSR. Secondary Surveillance Radar is covered in Chapter 13 of this book and in depth in Radio Navigation. There are, however, certain reserved codes (squawks) that have specific meaning, which you are required to know. At all times you should transmit the altimeter function (mode charlie) in addition to the reserved codes. The reserved transponder codes are:
•Mode A code 7700. This is the civil emergency code and is used unless a specific identification code has been allocated by a radar controller and the aircraft has been identified.
•Mode A code 7600. This is the squawk to indicate radio failure and should be used at all times when a failure occurs regardless of the ATC service being provided.
•Mode A code 7500. This code indicates unlawful interference. Its use does not imply that the fact is being generally advertised. Discretion and confidentiality will be preserved by the ATC authority until the pilot mentions the fact by RTF. A pilot may prefer to use the 7700 squawk to indicate the severity of the situation.
•Mode A code 7000. This code indicates that the aircraft is operating in an area where a radar service is available from an ATCU but the aircraft is not in receipt of the service. It implies that the aircraft is operating under VFR.
•Mode A code 2000. This code is used to indicate that an aircraft is entering an area where a radar service is available and will be requesting that service. Usually used by aircraft entering a domestic FIR from an Oceanic control area.
•Mode A code 0000. This code is reserved to indicate that the aircraft transponder is in some manner unserviceable or inaccurate.
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Restricted, Prohibited or Danger Areas
6.82 Specification. Each state has the right to restrict or prohibit flight in territorial airspace for reasons of security or safety. Such areas are known as danger areas (indicated by the letter D), restricted areas (indicated by the letter R) or prohibited areas (indicated by the letter P) and are detailed in the AIP. These are designated by a code identifying the area and showing the altitude (usually in 1000s of ft) to which the area extends. Areas may be either permanently active (PERM) or activated by NOTAM. The area designator (for instance - D001) cannot be re-used for a period of not less than 12 months after the closure of the previously designated area. This allows for a full reprint of the 1/2 million topographical charts so that no confusion can exist.
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Figure 6.15
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6.83 Visual Warning of Incursion. By day and night; a series of projectiles discharged from the ground at intervals of 10 secs, each showing on bursting red and green lights or stars, are used to warn aircraft that they are flying in or about to enter restricted, prohibited or danger areas.
INCURSION INTO RESTRICTED
OR DANGER AREAS
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If you see RED and GREEN ‘star shell’ pyrotechnics it means you are about to enter a restricted area or an active danger area
Figure 6.16
Signals for Aerodrome Traffic
6.84Non-radio Traffic. Non-radio traffic on or in the vicinity of an aerodrome is to keep a good look out for visual signals from ATC. Aeroplanes with radios are also to comply with instructions given visually. The lamp used by ATC to communicate (Aldis lamp) is directional with a narrow beam. If you see a signal light from the tower, you must assume that it is meant for you.
6.85Visual Signals. The following table gives the light and pyrotechnic signals used from ground to air:
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Aircraft in Flight |
Aircraft on the Ground |
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Steady Green |
Cleared to land |
Cleared for take-off |
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Steady Red |
Give way to other aircraft and |
Stop |
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continue circling |
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Green flashes |
Return for landing and await |
Cleared to taxi |
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landing clearance |
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Red flashes |
Aerodrome unsafe, do not land |
Taxi clear of the landing area |
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Land at this aerodrome after |
Return to the starting point on |
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White flashes |
receiving clearance to land and |
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Red pyrotechnic |
Notwithstanding any previous |
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(flare) |
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time being |
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Figure 6.17
6.86 Acknowledgement by Aircraft. To acknowledge receipt of a signal as per Figure 6.17, an aircraft may make the following:
•When in flight:
•During the hours of daylight, by rocking the aircraft’s wings
•During the hours of darkness, by flashing on and off twice the aircraft’s landing lights or, if not so equipped, by switching on and off the navigation lights twice.
•When on the ground:
•During the hours of daylight by moving the aircraft’s rudder or ailerons;
•During the hours of darkness by flashing on and off twice the aircraft’s landing lights or, if not so equipped, by switching on and off the navigation lights twice.
6.87 Visual Ground Signals. The following signals may be shown on an aerodrome, either in the signal square or at other locations on the apron or movement area. A signal square is usually located in front (aerodrome side) of a control tower (visual control room) and is to be visible from the air anywhere in the vicinity of the aerodrome. The purpose is to convey essential information to pilots unable to communicate by radio. Other signals, applicable to non-radio traffic on the ground are displayed from a signals mast (also in front of the control tower) or by means of indicator boards (information signs) located on or adjacent to the control tower. The absence of a signal square indicates that the aerodrome is not to be used by non-radio traffic. This is the case at Oxford, where due to high traffic density and trainee pilots in the circuit, non-radio traffic is considered hazardous.
Note: The use of any signal by any person shall only have the meaning assigned to it under the rule.
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6.88 Signals in the Signals Area. The following signals are displayed on aerodromes to pass information to non-radio aircraft. In the examination, you will be expected to interpret the meaning of a signal from a written description of the sign:
A white “T” signifies that take-offs and landings shall be in the direction of the shaft of the “T” (as indicated by the arrow).
A white disc added to the “T”, means that take-off and landing direction do not necessarily coincide.
A white dumb-bell indicates that aircraft movement on the ground is confined to paved, metalled or similar hardened surfaces.
A white dumb-bell with black stripes signifies that take-offs and landings are to be on a runway, but movement on the ground is not confined to pavements.
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A red and yellow striped arrow signifies that a right hand circuit is in force.
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A red panel with a yellow diagonal stripe signifies that the manoeuvring area is poor and pilots must exercise special care.
A red panel with a yellow cross signifies that the aerodrome is unfit for aircraft movements, and landings are prohibited.
A white “H” signifies that helicopters shall take off and land only within the area designated by the marking.
A red ‘L’ over a dumb-bell means that light aircraft are permitted to take off and land either on a runway or on the area designated.
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A white double cross means that glider flying is in progress.
Two or more white crosses indicate that the section of the runway or taxiway (where they would be yellow crosses) is unfit for aircraft movement. Orange and white boundary markers will delineate the limit of the unusable ground or runway.
Two yellow broken lines and two continuous lines signify the holding point closest to the runway. Outside of the notified hours for ATC, this is the closest point an aircraft or vehicle can approach to the runway for the purpose of giving way to aircraft landing or taking off. This is a ‘pattern A’ marking.
A yellow ‘ladder’ marking across the taxiway indicates a holding point other than the closest to the runway. Outside ATC hours it can be ignored. This is a ‘pattern B’ marking.
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A black letter “C” on a yellow background indicates where a visiting pilot should report on arrival.
A yellow St George’s cross indicates the position on the manoeuvring area where tow ropes and banner can be dropped.
6.89Signals Mast. The following signals are flown from the signals mast:
6.90 QDM Boards. A yellow board with two black numbers on is situated on the tower, and indicates the runway direction in use (QDM).
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6.91 Boundary Markers. Orange and white striped markers indicate the boundary of the manoeuvring area where it is not clearly defined.
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6.92 Wind Sleeve. A wind sleeve (windsock) indicates the wind direction and speed. (Large = 40 kt; medium = 30 kt; small = 20 kt) Max wind speed (i.e. 40 kt) Half wind speed (i.e. 20 kt) Calm
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