ATC, information and alerting services

Three services, different commitments

Information is useful without being a separation clearance.

Objectives and providers

ATS aims to prevent aircraft collisions, prevent collisions between aircraft and obstructions on the manoeuvring area, expedite orderly traffic, provide useful advice/information and notify/assist the appropriate organisations for aircraft needing SAR. The three basic services are ATC, flight information and alerting. ATC comprises area, approach and aerodrome control.

An ACC or assigned unit provides area control, APP or assigned tower/ACC approach control, and TWR aerodrome control. A flight information centre or assigned ATC unit provides FIS and alerting for its responsibility. Apron management may be assigned to the tower, another unit or the aerodrome operator under local arrangements; it is not universally a TWR function.

Clearance purpose and transfer

A clearance authorises a flight to proceed under specified conditions to prevent collisions within the service’s scope and maintain orderly traffic. Its five possible elements are aircraft identification, clearance limit, route, level(s) and changes, and other necessary instructions/information. Control movement of vehicles, people and towed aircraft on the manoeuvring area as needed to avoid conflicts.

During transfer, contact the next unit when instructed and use the assigned frequency/call sign. Transfer of communication and transfer of control need not occur at the exact same instant. In an emergency ATS can try the current/previous frequency, the expected next frequency and 121.5 MHz, with other available means.

FIS and ATIS

Keep the message’s origin, currency and purpose visible.

Flight information

FIS is provided to aircraft likely to be affected, including those receiving ATC or otherwise known to the relevant unit. It includes relevant SIGMET/AIRMET, volcanic activity and ash, radioactive or toxic releases, navigation aid changes, aerodrome conditions and other safety information. It can include collision hazards in uncontrolled/advisory airspace and available information relevant to safe continuation.

FIS does not relieve the PIC of decision-making responsibility or provide the separation service implied by an ATC clearance. An instruction, an advisory and a weather report must not be treated as equivalent. In a busy frequency, prioritise safety-critical information and clarify an ambiguous instruction.

Automatic terminal information

ATIS means automatic terminal information service. It provides routine arrival/departure information through voice and/or data link, normally for one aerodrome, with coordinated arrangements where appropriate. Voice ATIS uses a suitable discrete VHF channel or the specified navigation-aid voice channel; avoid confusion with a control frequency. Reports are updated promptly when significant changes occur and identified by sequential phonetic letters.

Typical content includes aerodrome and message identification, time, approach/runway information, runway conditions, transition level as applicable, operational notices, surface wind, visibility/RVR, weather, cloud, temperature/dew point and altimeter setting. Acknowledge the identifier on first contact. ATC can then correct changed information; an old letter is not proof that the weather is unchanged. English is available as required, with other language arrangements where appropriate.

When uncertainty becomes an emergency phase

Notify the rescue coordination centre; do not wait for every phase in sequence.

Who receives alerting

Alerting is provided to aircraft receiving ATC, other aircraft having filed a flight plan or otherwise known to ATS as far as practicable, and aircraft known or believed to be subject to unlawful interference. The responsible ATS unit initiates the appropriate phase and notifies the RCC, with the ACC/FIC coordinating the region’s alerting information.

INCERFA is uncertainty, including no communication within 30 minutes of when it should have been received or first unsuccessful attempt, whichever is earlier, or overdue arrival by 30 minutes after the last notified or ATS-estimated time, whichever is later, unless there is no doubt about safety. ALERFA is alert, including unsuccessful further enquiries, failure to land within five minutes of expected landing after clearance with no renewed communication, impaired operation short of likely forced landing, or suspected unlawful interference. DETRESFA is distress when evidence indicates grave and imminent danger, fuel exhausted or insufficient to reach safety, likely forced landing or unsuccessful alert enquiries warrant that conclusion.

Use the evidence, not a stopwatch alone

These triggers include important qualifications and exceptions; immediate evidence of distress can justify DETRESFA without first waiting through uncertainty and alert. Relevant information is passed to nearby aircraft to assist, except where disclosure of unlawful interference could aggravate the situation and other restrictions apply.

An arrival report can close the uncertainty; notify the responsible unit promptly after a safe landing. A missed radio call alone does not prove an accident, but it does require the prescribed attempt to establish the aircraft’s condition.

Can you apply the rules?

Four original questions. Choose from the facts, then review the explanation.