1 - VFR - Visual Flight Rules :

a) Visual Meteorological Conditions - VMC (also called VFR conditions) :

VFR flights are not authorized if the weather conditions are not at least equal to those specified below, known as the VMC (visual meteorological conditions). These are ICAO standard VMCs with general values. Contact your division for a detailed information about your country.

(1) The higher of 1 000 ft ASFC or 3 000 ft AMSL is often called the "S surface".

(2) As far as the minimum cruising distance from ground when flying VFR is 500 ft, you need a ceiling of at least 1500 ft to remain at a minimum of 1000 ft below clouds.  (a ceiling is defined as cloud cover of more than 50% - a FEW or SCT layer does not constitute a ceiling)

(3) May be less than 5 km / 3 SM but more than 1 500 m / 1 SM according to national rules (see your division training site). Also, for helicopters only, the required visibility may be less than 1 500 m / 1 SM.

For VFR flights at night, night VMCs are usually slightly higher than those above. 

(4) VFR is prohibited in class A airspace

Some countries have different VMCs. Particularly, some define the VMC according to the speed of the aircraft and according to the type of airspace.

b) Special VFR - SVFR :

As indicated above, VFR flights are prohibited in controlled airspace if visibility is less than 5 km / 3 SM or ceiling less than 1500 ft. However, a special clearance  can be delivered by the airport authority to enter or fly into a controlled airspace. Such a clearance is known as a Special VFR clearance. Specific weather minima are defined by the airport authority; however, the visibility can't be lower than 1500 m / 1 SM. 

The SVFR clearance is a authorization to fly into the controlled airspace with less than 5 km / 3 SM visibility or less than 1500 ft ceiling. It usually includes a prescribed route and altitude for spacing with IFR traffics.

One thing to note with a Special VFR clearance however, the PILOT MUST REQUEST this clearance if he wishes use this lower visual minimum.  The controller cannot offer the clearance without this request.  The controller's ability to grant this request lies with the local protocols as well as the IFR traffic density at the time.

c) Minimum and maximum levels :

VFR flights are to be carried out :

- at least 1000 ft ASFC (above surface) or above any obstacle within 600 m when overflying cities.

- at least 500 ft ASFC or above and from any obstacle in other cases.

- in lower airspace (below FL 200 in France, for instance; contact your division for an additional information about your country).

d) VFR cruising altitudes and levels :

As far as the general case is concerned, VFR flights use altitudes below the transition altitude and FLs ending by 5 above the transition level according to the semi-circular cruising system (see also L5-Altimetry) :

note: check the country for maximum VFR altitude.  For example, North/South America VFR must remain clear of the class A airspace, which begins at FL180.

e) Speed restriction :

The indicated airspeed is limited to 250 KIAS below 10000 ft AMSL or FL 100. However, if requested and approved by ATC, higher speeds can be accepted. Exceptions are for military jets for which such a restriction is not operational (common speeds for fighters are 350 KIAS into VFR patterns and between 400 and 550 KIAS for low level navigations).

f) VFR in controlled airspace :

VFR flights are not permitted in class A airspaces.

In order to enter or to fly into a controlled airspace (B-C-D classes), the pilot needs :

- to have an active transponder.

- to establish the radio contact with the control authority (say Teamspeak or text mode).

- to be cleared by the control authority and follow the ATC clearance.

In other words :

In A class airspaces, VFRs are not permitted.

In B-C-D class airspaces, VFRs are controlled flights for which a radio contact and a clearance are required.

In E-F-G class airspaces, VFRs are non-controlled flights. No radio contact nor clearance are required.

When flying into the VFR patterns of a controlled aerodrome, a VFR flight is also considered as controlled, involving radio contact and clearance as well.

g) Flightplan :

A flightplan is required only when :

- flying over seas or inhospitable regions.

- flying by night (unless you perform a local flight).

- crossing a border.

- when entering or flying into a controlled airspace => simplified flightplan (see below).

In other cases, no flightplan is required but it is recommended to file one. See L1-VFR-FP.

note: VFR flight in IVAO requires a flight plan with minimum information. See L1-VFR-FP.

Simplified FP : when flying VFR, you may be requested to file a FP to help the controller dealing with your flight into his/her area of responsibility. In such a case, fill in a simplified FP (with VFR quoted), just indicating :

- your type of aircraft.

- your departure airfield.

- your destination airfield.

- and of course the usual First name, Name and Home base.

Leave other fields blank.

This is quite easy to do, doesn't take more than 30 seconds and is quite useful for the controllers, or even for other pilots browsing the online pilots page when into uncontrolled airspace on UNICOM.

h) Change from VFR to IFR :

The pilot must inform the relevant ATC, file a flightplan (in IvAp) and require the permission to continue his flight on IFR.

i) Who is flying VFR ? :

 Most of the time, general aviation flights (with C182, PA28, DR40...) are carried out on VFR. They often remain at low altitude (below 10000 ft AGL). Military low level training is also carried out on VFR (or a military equivalent with specific rules).

2 - IFR - Instruments Flight Rules :

a) Instruments Meteorological Conditions - IMC (also called IFR conditions) :

Any weather conditions below those specified in 1-a) are considered as IMC. VFR flights are prohibited in IMC. Subsequently, when in IMC, pilots have to fly under IFR.

Note : IFR flights may be carried out in VMC too. 

b) Minimum level :

IFR flights are to be carried out :

- at least 1000 ft (2000 ft in mountain areas) above the highest obstacle within 8 km.

- at least at the minimum altitude or level mentioned on navigation maps and approach charts.

c) IFR cruising altitudes and levels :

As far as the general case is concerned, IFR flights use altitudes below the transition altitude and FLs ending by 0 above the transition level according to the semi-circular cruising system (see also L5-Altimetry) :

 (remember the phrase "NEODD-SWEVEN" - North and East ODD, South and West EVEN)

d) Speed restriction :

The indicated airspeed is limited to 250 KIAS below 10000 ft AMSL or FL 100. However, if requested and approved by ATC, higher speeds can be accepted. Exceptions are for military jets for which such a restriction is not operational (common speed for fighters is 300 KIAS for radar recovery or when executing an instrument approach - initial and intermediate legs).

e) IFR in controlled airspace :

In order to enter or to fly into a controlled airspace (A-B-C-D-E classes), the pilot needs :

- to have an active transponder.

- to establish the radio contact with the control authority (say Teamspeak or text mode).

- to be cleared by the control authority and follow the ATC clearance.

In other words : 

In A-B-C-D-E class airspaces, IFRs are controlled flights for which a radio contact and a clearance are required.

In F-G class airspaces, IFR are non-controlled flights. No clearance is required; however, the radio contact is mandatory.

f) IFR arrivals/departures :

IFR departures are to be carried out in compliance with SIDs (Standard Instrument Departures) or DPs (Departure Procedures) unless otherwise instructed by ATC. An IFR departure clearance at least includes :

- a SID or a reporting point, an altitude or a FL, a squawk code and the departure frequency or,

- a heading and an altitude or FL after departure, a squawk code and the departure frequency. 

IFR arrivals are to be carried out in compliance with STARs (Standard Terminal Area Arrivals) and instruments approach  procedures unless otherwise instructed by ATC or if being cleared for a visual approach.

IFR arrivals can be cleared for a visual approach if the pilot has the airfield is sight. Thus he/she is not requested to comply with the instruments approach and can proceed visually for landing.

g) Flightplan :

A flightplan is mandatory for IFR flights. See L1-IFR-FP.

h) Change from IFR to VFR :

This can be done only if the aircraft is in VMC and not into airspace requiring an IFR flightplan.

The pilot must inform the relevant ATC by announcing CANCEL IFR, modify his/her flightplan accordingly and resend it.

i) Who is flying IFR ? :

All commercial (business jets, airliners...) and most military transport flights  are carried out on IFR. Military jet aircraft may fly on IFR too. However, specific training (combat, air refueling...) are carried out under specific rules.

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