IFR flight planning is an acronym for Instrument Flight Rules which is a term applied to flight planning when the pilot intends to use on board instruments for the purposes of navigation. IFR is used when the conditions in which an aircraft will be flying are not deemed to be safe enough to rely on visual clues alone but will depend upon the use of electronic signals for navigation and certain instruments within the flight deck. It is usual to rely on IFR flight planning during darkness or poor weather conditions. If we want to put IFR into context then it is a good idea to understand the basics of VFR (Visual Flight Rules) flight planning. VFR flight planning is the name given to flights where the pilot is wholly reliant upon visual signs with regards to the safe navigation of the aircraft. VFR is far simpler than IFR in that the pilot may use his or her own judgment with regards to obstacles, height and cloud ceiling, whereas IFR requires a much more technical standpoint and also some extremely specialist training.
The distance between any aircraft and any obstacles which it may encounter during a flight is termed the “separation” and this is a very important factor in IFR flight planning. The separation must be maintained no matter what the weather conditions. Air Traffic Control maintains a close eye on any aircraft which is in controlled airspace to ensure that IFR aircraft are maintaining separation. This is done via clearance which involves looking closely at the routes of particular aircraft as well as the speed and height at which they are travelling. Air Traffic Control manages this by keeping tabs on IFR aircraft with the use of radar equipment. In some cases, an aircraft may be out of range of radar and it is then that a pilot must keep in contact with air traffic control via radio transmissions where aircraft position reports are given. During any IFR flight an aircraft in controlled airspace needs to receive clearance for each new part of the flight, as fresh clearance is given by Air Traffic Control, the pilot will also receive notification of how far they may fly before a new clearance is necessary. A clearance will also usually offer a route to follow as well as an altitude.
Although the rules of IFR flight planning are stringent, the ultimate responsibility for an aircraft will always rest upon the shoulders of the pilot. If the pilot of an IFR flight decides that even though clearance has been given it would be unwise of him to accept it, he has every right to refuse clearance and will in some cases do so. It is important to remember that although IFR flight planning is the ultimate in a safely planned journey, there can be no substitute for human judgement in some cases and this is why it is understood that a pilot must always have the final say.