Flight rules

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I was at the intersection waiting for the traffic light to turn green. Once it was green I took a right turn ... for about 2 seconds. I smashed my car against a standing one since I had forgotten I was in the UK. Traffic rules prevent accidents. One set of rules for the drivers. An exam to prove you know the rules.

The same is true in airspace. Flight rules are mainly there to prevent accidents. Pilots have to take an exam to prove they know the rules and yes, rules differ from country to country. There are rules on how to approach an airfield, rules about speed (240 knots maximum below 10,000 feet), rules about pilot qualifications, rules about aircraft maintenance, rules about distance to land objects, rules about noise, rules on how to use the radio etc etc.

Two sets of rules have become synonymous for a way of flying, VFR for Visual flying and IFR for Instrument flying.

Some layers can be identified in the flight rules.


Each country can define it's own set of rules. Countries work together in the ICAO so that most airspaces have similar rules. The airspace class gives guidance on the different types of airspace. Note: The linked Wikipedia articles provides a general set of rules, always check if these are applicable for the country you are flying in.

Controlled airspace

Controlled airspace means aircraft must identify themselves with the designated ATC. The aircraft will be directed to paths and altitudes to aid separation, prevent collisions and aid in take-off and landing. The pilot must request permission (clearance) from ATC for each change in course, speed and altitude. Most airfields have controlled airspace around them.

Communication rules within controlled airspaces in FlightGear:

  • Use FGCOM
    • FGCOM lets you control your aircraft without reading chat or paying attention reading a chat box.
    • FGCOM helps the ATC to control much more aircraft at the same time, because heard and spoken commands are much faster than chat.
  • read the Communications-article to learn more
  • A detailed description of how ATC-procedures should be executed and which different types of controlled airspaces can be managed in FlightGear is shown in the ATC-Turorial.

Entering controlled airspaces

In Flightgear every pilot has to contact the ATC (if there is any) via FGCOM or Chat and should obey the following syntax, when he is entering a controlled airspace:

PILOT: Callsign with you at FL180 for Heathrow. Information Alpha. 
Controller: Callsign, Radar Contact 51 miles out, alpha is current. d/m 8,000 and direct OCK please.

The pilot is reporting his altitude, his attentions, and the letter of the actual ATIS he got on the ATIS-frequency before. In this example, he is at flightlevel 180 (18,000 ft at QNH and reports that is going to land at London Heathrow Airport. The controller confirms that he has the incoming air-plane on its radar, 51 miles out. He also confirms that ATIS information Alpha is the latest information. Additional he advices the pilot to descend and maintain 8,000 ft.

Navigating in controlled airspaces

Leaving controlled airspaces

Regularly controlled airspaces in Flightgear

Uncontrolled airspace

Uncontrolled airspace means the pilot is fully responsible to avoid other aircraft and obstacles. There is no external radar or ATC to assist with this task.

Visual flight rules

VFR are applicable when the pilot can see around to navigate and to avoid other aircraft and obstacles. The altitude must be low enough to identify landmarks for navigation. The weather or minimal meteorological conditions to allow VFR are defined in Visual Meteorological Conditions (VMC). As can be expected one of the most important condition is good visibility. If VFR is not possible IFR must be used.

Controlled visual flight rules

CVFR are applicable when the pilot is entering controlled airspace. Most often near airports but also over areas with high risks. The pilot is not free to navigate anywhere and will have to follow ATC directions. Pilots (most often) are not required to be IFR certified. When weather conditions change a pilot can often request CVFR assistance from ATC.

Special visual flight rules

SVFR is basically the same as CVFR but pilots must be IFR certified and navigation must be instrument based. Any condition of VFR that is exempted can be called SVFR.

Night visual flight rules

In many countries flying VFR at night is not allowed, most often IFR must be applied. For the few countries that allow flying at night NVFR are applicable. These rules include things like landing lights and illuminated on-board equipment.

Instrument flight rules

IFR are applicable when VFR is not allowed. The weather or meteorological conditions when IFR is required is defined in Instrument meteorological conditions (IMC). Navigation is based on radio beacons and most often a pre-approved flight plan is required. The pilot must be certified to apply IFR. All scheduled commercial flights operate exclusively under IFR.

Airline flight rules

The owner of an aircraft has to follow the local flight rules. The employee of a airline that owns an aircraft not only has to follow the local flight rules, the employee also has to follow airline flight rules. The airline, just as the local legislator, has an interest in preventing accidents. The airline also prefers to make a profit. The airline flight rules can not contradict local flight rules but the airline flight rules can be tighter and broader. Examples,

  • Local flight rules allow one pilot with a max 4 passengers.
    • Airline flight rules dictate two pilots on one aircraft.
  • Local flight rules dictates a minimum rate of ascend so that aircraft get out of the low-altitude-danger-zone fast.
    • Airline flight rules dictate a max. rate of ascend to prevent too much fuel burn.
  • Local flight rules allow a VFR approach even when there is an ILS.
    • Airline flight rules disallows a VFR approach when there is an ILS.
  • Local flight rules allow a powerback (the use of reversers to push the aircraft backwards).
    • Airline flight rules disallows a powerback since the airline will have to pay for any damage and the additional fuel burn.

Aircraft flight manual

The Aircraft Flight Manual (AFM) is a legal document that describes limitations, operating procedures and performance of a specific aircraft. Older aircraft have manuals with different names but with the same legal status. Modern light aircraft have a Pilot's Operating Handbook (POH) that is part of the AFM. The owner of the aircraft is responsible to keep the AFM up-to-date. The AFM is an integral part of the aircraft. The AFM includes specific flight rules for the aircraft.

Vertical separation

Despite many articles on the internet telling an aircraft has to fly a specified altitude when flying a magnetic course and VFR or IFR there is not ONE rule for the world!!!

One system uses AGL as reference, the other AMSL, one system separates with 500 feet intervals, the other at 1000, one uses indicated altitude, the other absolute altitude. Check the rules that apply and ask ATC what altitude to fly (and on what reference).

Below a specified altitude the pilot has to set the altimeter on QNH, above the specified altitude on Standard Pressure. The moment when to reset the altimeter is named the Transition altitude and it differs from country to country, some use 18000 feet some use 3000 feet and there are many variations in between. To add to the confusion some regions require the flight level in meters.

Does this confusion sound a bit like driving on the right side in the UK?

More info (but you have to read carefully) is here: http://en.wikipedia.org/wiki/Flight_level

External articles