The two main flight rules that pilots must follow are the visual flight rules (VFR) and instrument flight rules (IFR). Understanding these two sets of regulations is critical for all pilots, as they dictate the specific requirements and procedures that must be followed during any given flight.
What are Visual Flight Rules (VFR)?
Visual flight rules (VFR) are the simpler set of flight rules that govern flying in clear weather conditions with good visibility. When operating under VFR, pilots must fly with at least 3 miles of visibility and stay at least 500 feet below, 1,000 feet above, and 2,000 feet horizontally away from clouds. This allows pilots to navigate and avoid other aircraft visually rather than relying on instruments.
Some key requirements when flying under VFR include:
- Maintaining minimum visibility and cloud clearance
- Flying at slower speeds (under 250 knots when below 10,000 feet)
- Using see-and-avoid techniques to maintain separation from other aircraft
- Avoiding major metropolitan areas and congested airspace when possible
- Filing a visual flight rules flight plan prior to departure
VFR flight plans can be filed to indicate the pilot’s general route of flight and provide search and rescue personnel with critical information should an emergency occur. However, VFR pilots do not have to stick to a predetermined route like pilots flying under instrument flight rules.
When can pilots fly under VFR?
VFR flight is only permitted when weather conditions allow pilots to see and avoid obstacles and other aircraft. The exact minimum visibility and cloud clearance requirements vary depending on the airspace and altitude. For example:
- In controlled airspace below 10,000 feet, pilots must have at least 3 miles visibility and stay 500 feet below clouds
- Above 10,000 feet in controlled airspace, pilots need 5 miles visibility and 1,000 feet of cloud clearance
- In uncontrolled airspace below 1,200 feet above ground level (AGL), pilots need just 1 mile visibility and clear of clouds
- In uncontrolled airspace above 1,200 feet AGL, pilots need 3 miles visibility and 500 feet cloud clearance
VFR flight is only allowed when the weather meets the visibility and cloud clearance minimums for that specific airspace. Flying VFR into instrument meteorological conditions (IMC) where visibility is low or clouds are dense is extremely hazardous and illegal in most situations.
What are Instrument Flight Rules (IFR)?
Instrument flight rules (IFR) are the more complex flight rules that allow pilots to fly in almost all weather using cockpit instruments and navigation aids rather than relying on good visibility. IFR permits pilots to fly through clouds and in lower visibility by placing more stringent requirements on aircraft equipment, pilot certification, and precise routing.
Key requirements for instrument flight rules include:
- More advanced instrument cockpit equipment and pilot training
- Clearance from air traffic control for all legs of flight
- Following predetermined routes, procedures, and instructions
- Maintaining constant two-way radio communication with air traffic control
- Filing and following complex IFR flight plans
Pilots must meticulously plan instrument flights and obtain specific clearances from air traffic control. While this is more work than visual flying, it provides pilots with the ability to safely fly through low visibility and cloudy conditions.
When do pilots fly under IFR?
Instrument flight rules are used any time weather conditions do not allow for VFR flight. This includes situations where:
- Visibility is lower than VFR minimums
- Clouds are dense or ceilings are lower than VFR cloud clearance requirements
- Other meteorological conditions like precipitation or thunderstorms reduce visibility
- Flying into known or forecast icing conditions aloft
- Taking off or landing at an airport where visibility is low
Essentially, a pilot flies under IFR whenever actual or expected weather conditions prevent maintaining visual separation and obstacle/terrain clearance. This allows much greater access to the airspace system, as pilots do not have to only fly in perfect VFR weather.
Differences Between VFR and IFR
While both sets of flight rules have the same objective of safety, VFR and IFR have some key differences in their procedures and requirements:
| VFR | IFR |
|---|---|
| Visual navigation – pilot must see outside aircraft reference points | Navigation using instruments and radio aids |
| Maintain own separation from obstacles and other aircraft visually | Air traffic control provides separation services |
| More pilot flexibility in choosing route and altitude | Must follow predetermined clearance routes and instructions |
| Good weather visibility required | Can fly through low visibility and clouds |
| Less stringent equipment and training requirements | Aircraft and pilot must be IFR certified |
| No clearances needed from air traffic control | Clearances required for all legs of flight |
| Less detailed flight plan requirements | Strict IFR flight plan must be filed and followed |
While operating rules may vary by country, VFR generally affords pilots more flexibility while IFR provides access to more airspace and weather conditions. Most pilots obtain qualifications to fly both VFR and IFR.
VFR Flight Plans vs. IFR Flight Plans
The type of flight plan that pilots must file depends on whether they are flying VFR or IFR. While VFR flight plans are simpler, IFR flight plans require more detail and must be strictly followed.
VFR Flight Plans
VFR flight plans contain basic information about the planned flight that pilots optionally file before departure. Key components include:
- Aircraft identification number
- Aircraft type and color
- Departure and destination airports
- Proposed departure time and enroute time
- Altitude or flight level requested
- Route of flight
- Number of people on board
While sticking to the proposed route is recommended, VFR flight plans can be amended in flight as needed. VFR plans are an important tool for alerting others in the case of an emergency.
IFR Flight Plans
IFR flight plans contain extensive details on every segment of the flight and must be filed and approved before departure. Information includes:
- Departure airport, routes, and destination
- Proposed altitudes and flight levels
- Time estimates for each route segment
- Alternate airports for diversion
- Amount of fuel onboard
- Aircraft equipment capabilities
Any deviations from the IFR flight plan require amended clearances from air traffic control. IFR plans provide controllers with the necessary data to safely separate instrument flights.
Pilot Certification Requirements
Pilots must obtain specific certifications and ratings to operate under VFR and IFR flight rules:
VFR Certification
To act as pilot-in-command of an aircraft under VFR, pilots must hold at minimum a third-class FAA medical certificate and a private pilot certificate. However, the private pilot certificate does not permit VFR flight into busy, controlled airspace around major airports. For this, pilots need an instrument rating or commercial pilot certificate.
IFR Certification
Instrument flight requires an instrument rating in addition to a private, commercial, or airline transport pilot certificate. Earning an instrument rating involves extensive training on flying by reference to instruments, navigating under IFR, and instrument approach procedures. Pilots must demonstrate proficiency by passing a knowledge exam and instrument rating practical test.
In most countries, only instrument rated pilots can operate under IFR. IFR flight is prohibited without proper certification and aircraft equipment.
Equipping Aircraft for VFR and IFR
For both VFR and IFR operations, an aircraft must meet certain equipment requirements to ensure it can operate safely:
VFR Equipment
Aircraft flying under visual flight rules must have:
- Airspeed indicator
- Altimeter
- Magnetic compass
- Master and navigation lights for night flying
- Emergency locator transmitter (ELT)
- Transponder with altitude reporting
While not required, having a VHF radio allows pilots to monitor air traffic control and weather broadcasts.
IFR Equipment
Instrument flight requires more advanced avionics and instrumentation, including:
- Attitude indicator/artificial horizon
- Heading indicator/directional gyro
- Airspeed indicator
- Altimeter
- Vertical speed indicator
- Turn coordinator
- VOR and glideslope receivers
- At least one radio for communication with ATC
- Transponder with altitude reporting
- ADF, DME, or GPS navigation
IFR aircraft must also meet pitot-static system and electrical power redundancy requirements. Advanced GPS navigation and autopilot systems are very common for smoother instrument flying.
Conclusion
Following the correct set of flight rules is critical to maintaining the safety and orderliness of the airspace system. VFR allows more flexibility for pilots but requires good weather and visibility. IFR provides access to more flying conditions but places greater responsibility on pilots and air traffic control. All pilots are safer when they fully understand the differences between these two sets of regulations.