... You may! - You MUST! ...
OBJECTIVES:
- explain the difference
- when to use clearance or when to use an instruction?
Air Traffic Control CLEARANCE: you MAY...
A clearance is an authorisation that allows a pilot to do something...
Example: "Cleared FL110" means that FL110 is available and that the pilot MAY start his descent NOW or WAIT to start his descent until he reaches his Top of Descent point.
Depending on the phase of flight it relates to, a clearance can be called either a:
- taxi clearance
- take-off clearance
- departure clearance
- en-route clearance
- approach clearance
- landing clearance
Air Traffic Control INSTRUCTION: you MUST...
An instruction is an action to be executed without delay...
Example: "Descend to FL110" means that a pilot MUST descend NOW to FL110.
Who issues clearances and instructions?
ATC clearances and instructions are given by the Air Traffic Controller who controls the airspace in which the aircraft is flying or about to fly in. They are given to prevent collision between aircraft within controlled airspace.
Clearances and instructions shall be given according to the traffic situation BUT aircraft in a declared emergency (engine problems, fuel shortage, seriously ill passenger,...) have priority over other flights!
Pilots always need a clearance BEFORE starting a flight in or through controlled airspace.
How to obtain a clearance?
A clearance shall be requested by FIRST filing a Flight Plan (FPL) BEFORE contacting ATC.
A pilot MAY:
- request another clearance if the previous one is not suitable (eg. when he receives a SID to the North for a flight to the South)
- refuse a clearance, if it is dangerous for the safety of his flight (eg. vectoring into a thunderstorm)
ATC MUST:
- advise the pilot if traffic conditions do not permit to follow his request for another route or level
AND
- offer an alternative clearance or instruction if a pilot is not able to comply with the route or level he received
ATC MAY NEVER:
- refuse a clearance for any other reason than to prevent collisions
- give a clearance which violates any rules or regulations
In general, clearances shall contain:
- AIRCRAFT CALLSIGN: "GOL737"
and one or more of the following:
- CLEARANCE LIMIT: "cleared to POINT"
- ROUTE: "via WY4D arrival"
- LEVEL: "descend to FL90"
- INSTRUCTIONS and/or INFORMATION: "expect runway 19 "
Clearance limit
A clearance limit is the furthest point during flight or taxi to which you are cleared and beyond which you may not proceed (except when in radio failure).
Any significant point such as a VOR, a FIX, an aerodrome, a taxiway or FIR boundary can be used as a clearance limit. Unlike in real-life, on VATSim there's not always ATC available along the route of flight all the time, so the Aerodrome of Destination shall mostly be the clearance limit.
Readback
A READBACK means that the PILOT REPEATS the clearance or instruction that he received from ATC.
It is important to note that the clearance does not become a clearance until the pilot has READ BACK THAT CLEARANCE TO THE CONTROLLER
What's the use?
ATC SHOULD ALWAYS LISTEN to the readback from the pilot to make sure that his clearance or instruction has been correctly understood.
If a readback is NOT CORRECT, ATC MUST immediately repeat the clearance or instruction and check the pilot's readback again. Should the controller fail to do so, then he will get the blame when things go wrong (not the pilot!!).
ALWAYS readback:
- ALL clearances or instructions
- QNH
- Transition Level
- Runway-in-use
- Squawk