... How to navigate on instruments if only ...
OBJECTIVES:
- To tell you more about Instrument Flight Rules (IFR)
- Its purpose and how to apply them
Instrument Meteorological Conditions (IMC)
When weather is below the VMC minima, we are in Instrument Meteorological Conditions (IMC).
When in IMC, you may only fly according to the Instrument Flight Rules (IFR).
Note : IFR flights may be carried out in VMC too, but VFR flights may not be carried out in IMC.
Instrument Flight Rules (IFR)
a) Aircraft equipment
To fly according the Instrument Flight Rules (IFR), the aircraft must be equipped with instruments and navigation equipment to be able to fly in Instrument Meteorological Conditions.
The pilot should also be trained to use this equipment properly.
b) IFR in controlled airspace
In order to enter or to fly IFR into airspace class A, B, C, D and E, the pilot needs to:
- contact ATC by Voice or text mode
- obtain an ATC clearance (see as well sub f. below).
c) Day or night
IFR flights have no day or night limitations like VFR flights, since they are not depending on light for their visual navigation, but on their instruments.
d) Minimum and maximum levels and speeds
Except when landing or during take-off, IFR flights are to be flown at least at the minimum altitude or flight level mentioned on navigation maps and approach charts.
Where no minimum flight altitude is defined, the aircraft shall remain
- at least 2.000 ft above any obstacle within 8 km (+- 5NM) of the estimated position of the aircraft when
- over high terrain
- in mountaneous areas
- at least 1.000 ft above any obstacle within 8 km (+- 5NM) of the estimated position of the aircraft elsewhere
Maximum levels may be imposed for a portion of a flight because of airspace limitations, ATC procedures or flow restrictions. These maximum levels mostly apply during climb to or after the descent from cruising level.
Note: the word "level" is used for either "altitude" or "flight level"
e) Cruising Altitudes and Flight Levels
IFR flights in level cruising flight, when operated above 3.000 ft AMSL (Above Mean Sea Level), shall fly at a level according to the track as specified in the semi-circular cruising system in use.
Note: the word "level" is used for either "altitude" or "flight level"
For further details on the semi-circular cruising system, see the Chapter about Cruising levels".
IFR Levels end by 0. (See table below)
f) Speed restriction
The indicated airspeed is limited to 250 KIAS below 10.000 ft AMSL or FL 100. When approved by ATC, higher speeds can be accepted.
| On VATSim, it has been agreed that as a general rule, Military fighter and Military fast-jet aircraft may fly up to 350 kt IAS (Indicated Air Speed) below 10.000 ft / FL100 in both controlled and uncontrolled airspaces. |
g) Flightplan
A Flight Plan is always required for IFR flights.
For details, read the Chapter about "Filing a flightplan", Vatsim Pilot Resource Center
h) ATC clearances for IFR flights
A flightplan has to be filed first before an ATC clearance can be asked.
For IFR flights, an ATC clearance is required when:
- flying within Classes A, B, C, D and E airspace*
- operating at controlled aerodromes
*In other words:
In Class A, B, C, D and E airspaces, IFR flights are controlled flights for which a radio contact and a ATC clearance are required.
In Class F and G airspaces, IFR flights are non-controlled flights. No ATC clearance is required but radio contact is mandatory.
i) Change from IFR to VFR
A pilot shall inform ATC that he will change from IFR to VFR only if the aircraft is in VMC and he intends to continue the flight in VMC for a reasonnable period of time
ATC may refuse to cancel IFR when the aircraft is flying in airspace Class A.
When approved, ATC shall modify the flight rules in the flightplan and resend it to make ensure that the next ATC receives the updated information.
j) Who is flying IFR?
All commercial (business jets, airliners...) and military transport flights along airways are carried out on IFR.
Military jet aircraft may fly on IFR too, but when flown as Operational Air Traffic (OAT) for specific training, missions, air refuelling... they are carried out under specific rules that you will find at the Special Operations Department (SOD).