How Airline Traffic is Protected from Other Aircraft
Normally airliner traffic fly's in Controlled Airspace from shortly after take off until it lands. The flight is controlled by an Air Traffic Controller using a radar screen. The Controller will know the flight plan of the aircraft and will prevent other aircraft from coming to close to each other. This the controller does by applying separation standards. These can be 5 miles apart at the same height for example. Or ten minutes behind each other. Or a 1000 ft above or below the aircraft within 5 miles or other permitted distance depending on the circumstances.
Light Aircraft Flying Club Pilots are not allowed to fly in Controlled Airspace unless the aircraft is fully radio equipped and the pilot holds an instrument rating. The instrument rating is a test that the pilots must do at regular intervals and pass or they cannot fly in Controlled Airspace. Therefore most light aircraft fly outside of Controlled Airspace either to the side of it or below it as pilots do not hold instrument ratings. Controlled airspace normally starts at the lowest level of about 3000 ft and gets higher the further from the major airport. Around airports are special rules areas. All aircraft pilots must get permission of the Airport Control Tower or Approach Control before flying in this area. Instructions must be obeyed. This way the flying club pilot can approach ,land and take off or fly through the airport approach area.. The controller will fit the aircraft in between airliners which have major priority. Across the country airways are created which are 10 miles wide. Airliners normally fly along these. This leaves plenty of space for the flying club pilot to fly in for pleasure either underneath the airway or to the side.
Requirements for Flying in Controlled Airspace
The pilot must have an instrument rating and if flying at night ,a night rating. If the aircraft is twin engine aircraft a twin engine rating is also required for the type of aircraft the pilot is flying. The aircraft must be fully equipped with radio navigation and voice radios. A flight plan detailing the route must be filed and approved with Air Traffic Control before the flight. Clearance must be obtained before entering and leaving controlled airspace. All Air Traffic Controller's Instructions must be obeyed and repeated back so that the controller can check the pilot has understood correctly. If the pilot thinks this will endanger the aircraft the pilot must challenge the controller and take any avoiding action.
With regular scheduled flights the flight plans are stored in the Air Traffic Control Computer permanently. The flight plan activates shortly before take off automatically. The pilot then only has to call ATC to get the clearance for the flight. Flight planning is now a skill of its own. If the aircraft is flying through Europe the flight has to follow set routes . These are contained in the Route Availability Document (RAD). This changes each month. Many airlines now employ special flight planning companies to do the flight planning and submission to Air Traffic Control. The pilot is given a copy on signing on for the flight so that s/he can program the flight management computer on the aircraft.
If delayed departure time is occurring and changes are required perhaps because the weather requires a diversion the pilot must tell ATC so that the planned departure time or route can be amended. otherwise if the flight fails to arrive within half an hour of planned arrival time then an air sea rescue operation would occur looking for the flight. This part of live planning is normally done with the handling agents or pilot on the radio.
For a flight to be able to proceed every Air Traffic Control Centre which the flight is passing through must accept the aircraft before take off. This is co ordinated by the Central Flow Management sector of Eurocontrol in Europe. If any area gets too congested on the route flow control regulations are brought in to limit the aircraft numbers in the sector for safety. From this slot times are issued to aircraft as to when they can depart. If the aircraft cannot make the slot time then the flight cannot take off until a new one is given. This can be anything from 15 minutes delay upwards. Pressure is therefore on pilots and ground staff to ensure flights depart on time. Bad weather and strong headwinds can play havoc with turnaround times and lost slot times.
At major airports Standard Instrument Departures (SID) are flown on take off. These routes are published in charts. The pilot is told which departure to fly by ATC. The SID will take the aircraft into the airway, and then the pilot fly's along the airways, using radio beacons and waypoints shown on charts. As the aircraft nears the destination ,the pilot will fly a Standard Arrival Procedure known as STAR. again shown on the chart. This will take the aircraft to an Initial Approach Fix where the aircraft may fly a race track holding pattern ( which takes 4 minutes to fly around once.) If no delay an instrument approach chart is used to get the aircraft positioned onto final approach for landing. At major airports Approach Air Traffic Controllers, will give the pilot instructions on headings to fly speeds and heights to slow or descend to. Eventually the controller will tell the pilot to fly a certain heading until established on final approach where the pilot can either visually land the aircraft or use instruments to assist . At this point the aircraft is handed over to the Tower Controller for landing. (This procedure is known as Radar Vectoring )
Notes
After Landing or before take off the Ground Controllers control the aircraft from and to the gates and the runway. Clearance to enter controlled airspace is obtained through Ground Control or often a frequency known as Delivery.
Approach Control ,for the major London Airports, is now done from the London Air Traffic Control Centre, and not from the Towers at the airports. All controlled airspace traffic in UK is Controlled from one of two London Centres or Scottish Centre with a centre in Manchester.
Some Airways are one way only. So outbound and inbound routes do not always follow the same route. Airways up to 24500 Ft are known as Low Level Airways . Anything above that is High Level Airways Charts can be purchased showing the airways. They are £3 each at present.
Sometimes airliners may have to fly in uncontrolled airspace between an airport and an airway. Normally radar advisory services from military units or other airfields with radar can assist the pilots in identifying other traffic. Also most airliners have TCAS systems which can assist pilots .