Instrument flight rules
Any aircraft operating under VFR must have the required equipment on board, as described in FAR Part 91.205[5] (which includes some instruments necessary for IFR flight).
In many countries commercial airliners and their pilots must operate under IFR as the majority of flights enter Class A airspace.
[9] Procedures and training are significantly more complex compared to VFR instruction, as a pilot must demonstrate competency in conducting an entire cross-country flight solely by reference to instruments.
In the United States, a flight operating under IFR is required to provide position reports unless ATC advises a pilot that the plane is in radar contact.
In addition, a clearance typically provides a heading or route to follow, altitude, and communication parameters, such as frequencies and transponder codes.
Despite the protection offered by flight in controlled airspace under IFR, the ultimate responsibility for the safety of the aircraft rests with the pilot in command, who can refuse clearances.
It is essential to differentiate between flight plan type (VFR or IFR) and weather conditions (VMC or IMC).
The weather is considered to be MVFR or IMC when it does not meet the minimum requirements for visual meteorological conditions (VMC).
A scenario is a VFR pilot taking off in VMC conditions, but encountering deteriorating visibility while en route.
Continued VFR flight into IMC can lead to spatial disorientation of the pilot which is the cause of a significant number of general aviation crashes.
Also possible in many countries is "Special VFR" flight, where an aircraft is explicitly granted permission to operate VFR within the controlled airspace of an airport in conditions technically less than VMC; the pilot asserts they have the necessary visibility to fly despite the weather, must stay in contact with ATC, and cannot leave controlled airspace while still below VMC minimums.
For example, Reno-Tahoe International Airport (KRNO) in a mountainous region has significantly different instrument approaches for aircraft landing on the same runway surface, but from opposite directions.
[14] Because IFR flights often take place without visual reference to the ground, a means of navigation other than looking outside the window is required.
[citation needed] Specific procedures allow IFR aircraft to transition safely through every stage of flight.
These procedures specify how an IFR pilot should respond, even in the event of a complete radio failure, and loss of communications with ATC, including the expected aircraft course and altitude.
[citation needed] To fly under IFR, a pilot must have an instrument rating and must be current (meet recency of experience requirements).
In the United States, to file and fly under IFR, a pilot must be instrument-rated and, within the preceding six months, have flown six instrument approaches, as well as holding procedures and course interception and tracking with navaids.
