Cfrtjryk

Although I have worked as ATC more than 5 years(not US), I don't know the exact definition of VFR and IFR.

Of coure, I know that under VFR, pilot mainly use their eyes to navigate, but I want to know more exact and offical reference.

I tried to search these via google but failed to find offical reference such as ICAO annex or FAA regulations.

Could you guys help me to find the offical reference relating to VFR and IFR?

The Rules of the Air are defined by ICAO and made applicable with few deviations in the ICAO member states.

ICAO Annex 2 Rules of the Air, defines in addition to the general rules, the Visual Flight Rules (VFR) and the Instrument Flight Rules (IFR). Flights shall be in compliance with either of them.

2.2 Compliance with the rules of the air

The operation of an aircraft either in flight or on the movement area of an aerodrome shall be in
compliance with the general rules and, in addition, when in flight,
either with:

a) the visual flight rules; or

b) the instrument flight
rules.

Chapter 5 of Annex 2 contains the Instrument Flight rules.

Chapter 4 of Annex 2 contains the Visual Flight Rules.

4.1 Except when operating as a special VFR flight, VFR flights shall be conducted so that the aircraft is flown in conditions of visibility and distance from clouds equal to or greater than those specified in Table 3-1.

Table 3-1 is summarized below.

+---------------------------+-------------------+---------------------+-----------------------------+

|      Altitude band        |   Airspace class  |  Flight visibility  |     Distance from cloud     |

+---------------------------+-------------------+---------------------+-----------------------------+

| At and above 3 050 m      | A*** B C D E F G  |        8 km         | 1 500 m horizontally        |

| (10 000 ft) AMSL          |                   |                     | 300 m (1 000 ft) vertically |

+---------------------------+-------------------+---------------------+-----------------------------+

| Below 3 050 m (10 000 ft) | A*** B C D E F G  |        5 km         | 1 500 m horizontally        |

| AMSL and above 900 m      |                   |                     | 300 m (1 000 ft) vertically |

| (3 000 ft) AMSL, or above |                   |                     |                             |

| 300 m (1 000 ft) above    |                   |                     |                             |

| terrain, whichever is the |                   |                     |                             |

| higher                    |                   |                     |                             |

+---------------------------+-------------------+---------------------+-----------------------------+

| At and below 900 m        |   A*** B C D E    |        5 km         | 1 500 m horizontally        |

| (3 000 ft) AMSL, or 300 m |                   |                     | 300 m (1 000 ft) vertically |

| (1 000 ft) above terrain, +-------------------+---------------------+-----------------------------+

| whichever is the higher   |        F G        |        5 km**       | Clear of cloud and with the |

|                           |                   |                     | surface in sight            |

+---------------------------+-------------------+---------------------+-----------------------------+

* When the height of the transition altitude is lower than 3 050 m (10 000 ft) AMSL, FL 100 should be

  used in lieu of 10 000 ft.

** When so prescribed by the appropriate ATS authority:

    a) flight visibilities reduced to not less than 1 500 m may be permitted for flights operating:

        1) at speeds that, in the prevailing visibility, will give adequate opportunity to observe 

           other traffic or any obstacles in time to avoid collision; or

        2) in circumstances in which the probability of encounters with other traffic would normally 

           be low, e.g. in areas of low volume traffic and for aerial work at low levels.

    b) HELICOPTERS may be permitted to operate in less than 1 500 m flight visibility, if manoeuvred 

       at a speed that will give adequate opportunity to observe other traffic or any obstacles in 

       time to avoid collision.

*** The VMC minima in Class A airspace are included for guidance to pilots and do not imply

    acceptance of VFR flights in Class A airspace

For Air Traffic Management purposes, ICAO Doc 4444 gives more detail of how both types of flights are treated by ATC.

National regulations may deviate from ICAO regulation. If they do deviate, the deviation have to be published in the Aeronautical Information Publication of the country.

In the US, the definition of VFR depends on which airspace you are operating in. The rules for VMC (Visual Meteorological Conditions) are listed in FAR 91.155. The definition of IFR is easy. If conditions are less than the minimums listed for the type of airspace, you are in IFR conditions.

VFR is a combination of being in good conditions ( having 3SM visibility, and staying 500/1000/2000 ft clear of clouds), and being responsible for your own navigation, terrain clearance and traffic-avoidance (see-and-avoid).

Anytime you're not operating under VFR rules in VMC conditions, you are either IFR or operating illegally!

You can be following IFR rules even when conditions are good.

You cannot be VFR when you have an open IFR plan.

"In order to operate under Visual Flight Rules, visual meteorological
conditions (3 Statute Miles (SM) visibility and at least 1,000'
ceilings) must exist In addition to operating within VMC conditions,
pilots must maintain specific distances from clouds, depending on
airspace [Figure 1]"

https://www.cfinotebook.net/notebook/rules-and-regulations/special-vfr