Airspace is classified into different levels to help pilots navigate safely, with controlled separations managed by air traffic controllers. Aircraft vary in size and speed, so they cannot all fly at the same altitude. Classifying airspace allows separation by flight type—Instrument Meteorological Conditions (IMC) under IFR and Visual Meteorological Conditions (VMC) under VFR—and by speed. High-speed aircraft follow dedicated routes, while slower aircraft have their own designated paths. Speed limits and approaches are published on charts to help crews navigate safely, including specific instructions for arrivals in busy airspaces.
In congested airspaces, aircraft must often proceed to holding points where they follow standard turns at set speeds and altitudes, awaiting clearance for landing. The classification of traffic is categorized as follows:
- Category A
- Category B
- Category C
- Category D
To monitor and manage traffic in controlled airspaces, airports use radar systems, which allow controllers to track direction and speed in real-time. Controllers may assign specific transponder codes for easy identification on the radar. In busy international airports, multiple radio frequencies manage traffic flow, with each stage of approach or departure handled on a dedicated frequency. Instructions are provided through radio communications, and frequencies for approach, tower, and ground are displayed on charts.
Traffic may be required to enter holding patterns in busy airspace, where they follow standard turns at specified speeds and altitudes until cleared for landing. For international departures, procedures differ slightly from those at local airports. Clearances and flight plans must be received before starting engines, ideally 30 minutes before departure for domestic flights and an hour for international routes. Clearances must be noted to ensure accurate readbacks, serving as a record of the flight plan in case of emergencies. Departure frequency follows this sequence:
- Ground frequency
- Tower frequency
- Departure frequency
Airspace classifications, which separate flights and reduce traffic congestion, are designated alphabetically. This allows controllers to prioritize and manage traffic more effectively. In controlled airspace, radar is often used for additional monitoring, with transponders aiding in aircraft identification. Classes of airspace include:
- Class A: Extends from 18,000 feet and above. Only IFR flights are permitted, as these altitudes generally lack visual references and can present icing hazards. Aircraft operating here must have anti-icing systems to prevent ice formation.
- Class B: From 14,000 to 18,000 feet, accommodating both IFR and VFR flights. Aircraft in this range are equipped to prevent icing issues and often transition to or from Class A or C airspace.
- Class C: Used for both IFR and VFR flights with managed separations. This level sees a mix of small, single-engine aircraft and large aircraft descending toward airports, often on final approach.
- Class D: Provides traffic information for both IFR and VFR flights, typically used for aircraft approaching landing or holding patterns close to the airport. Pilot training often occurs here due to its lower altitude.
- Class E: Extends from 700 feet up to 18,000 feet, allowing both IFR and VFR operations without radar control, but with traffic information available through designated frequencies.
- Class G: Extends from the ground to 700 feet, primarily for drones and other remote-controlled aircraft.
In emergencies, priority is always given to aircraft needing urgent landing. Classification reduces congestion, simplifies communication, and prioritizes IFR flights except in emergencies. Pilots are trained in these classifications to reduce ATC workload and ensure safe, efficient navigation through different airspaces.
In the past, mid-air collisions sometimes resulted from misunderstandings between cockpit devices like TCAS (Traffic Collision Avoidance System) and ATC communications. This issue has led to advancements in onboard collision-avoidance systems, further enhancing air safety.