Understanding Visual Flight Rules (VFR) and Instrument Flight Rules (IFR) Operations

VISUAL FLIGHT RULES (VFR) OPERATIONS

Visula flight rules (VFR) are a set of regulations under which a pilot operates an aircraft in weather condition generally clear enough to allow the pilot to see where the aircraft is going. Specifically, the weather must be better that basic VFR weather minima, i.e. in visual meterological conditions (VMC), as speified in the rules of the relevant aviation authority. The pilot must be able to operate the aircraft with visual reference to the ground, and by visually avoiding obstructions and other aircraft.

If the weather is less than VMC, pilots are required to use instruments flight rules, and operation of the aircraft will be primarily referencing the instruments rather than visual reference. In a control zone, a VFR flight may obtain a clearance from air traffic control to operate as special VFR.

It is possible and fairly straightforward, in relatively clear weather conditions, to fly solely by reference to outside visula cues, such as horizon to maintain orientation, nearby buildings and terrain features for navigation, and other aircraft to maintain seperation. This is known as operating the aircraft under visual flight rules (VFR), and is the most common mode of operation for small aircraft. However, it is safe to fly VFR only when these outside reference can be clearly seen from a sufficicent distance; when flying through or above clouds, or in fog, rain, dust or similar low-level weather conditions, these references can be obscured. Thus, cloud ceilingand flight visibility are the most important variables for safe operations during all phases of flight. The minimum weather conditions for ceiling and visibility for VFR flights are defined in FAR (Federal Aviation Regulations) part 91.155, and vary depending on the type of airspace in which the aircraft is operating, and on whether the flight is conducted during daytime or night time. However, typical daytime VFR minimums for most airspace is 3 statute miles of flight visibility and a distance from clouds 0f 500 feet below, 1,000 feet above, 2,000 feet horizontally. Flight conditions reported as equal to or greater than these VFR minimums are referred to as visual meteorological conditions (VMC).

Any aircraft operating under VFR must have the required equipment on board, as described in FAR part 91.205 (which includes sone instruments necessary for IFR flights). VFR piloy may use cockpit instruments as secondary aids to navigation and orientation, but are not required to; the view outside of the aircraft is the primary source for keeping the aircraft straight and level (orientation), flying to the intended destination (navigation), and avoiding obstacles and hazards (seperation).

Visual flight rules are generally simpler than instrument flight rules, and require significantly less training and practice. VFR provides a great degree of freedom, allowing pilots to go where they want, when they want, and allows them much wider latitude in determing how they get there.

INSTRUMENT FLIGHT RULES (IFR) OPERATIONS

The U.S. Federal Aviation Administration's (FAA) Instrument flying Handbook defines IFR as: "Rules and regulations established by the FAA to govern flight under conditions in which flight by outside visual reference is not safe. IFR flight depends upon flying by reference to instruments in the flight deck, and navigation is accomplished by reference to electronic signals.

IFR and IMC are similar. IFR stands for instrument flight rules - the set of rules that govern aircraft that fly in IMC, or instrument meteorological conditions. In general terms, intrument flying means flying in the clouds. More specifically, IMC defined as weather that is "below the minimums presecribed for flight under Visual Flight Rules."

It's called instrument flight because the pilot navigates only by reference to the instruments in the aircraft cockpit. Flying in the clouds (IMC) requires an IFR flight plan and an instrument ratings.

Flying by instruments, without any outside references sounds dangerous, but it's very safe once you've received the proper training. Training includes learing how touse navigational aids like VORs (Very High Frequency Omi-Directional Range), ADF (Automatic Direction Finding) and GPS (Global Positioning System) and how to fly approaches using an instrument landing system (ILS). Instument training also includes a comprehensive study of weather system and reports, icing conditions, and how the human body respond to spatial disorientation.