Air Traffic Control Procedures

Aircraft must be equipped with suitable instruments and navigation equipment appropriate to the route to be flown.

Clearances are issued solely for expediting and separating air traffic and are based on known traffic conditions that affect safety in aircraft operation.
If a pilot receives a clearance or instruction that cannot be complied with, the controller shall be advised using the phrase "UNABLE" supplemented by the reason for the inability.
ATC clearances do not constitute authority to violate any applicable regulations for promoting the safety of flight operations or for any other purpose.
Tehran ACC shall issue such ATC clearances as are necessary to prevent collisions and to expedite and maintain an orderly flow of air traffic.

Clearances are issued for expediting and separating air traffic and are based on known traffic conditions that affect safety in aircraft operation.
The issuance of air traffic control clearances by Tehran ACC constitutes authority for an aircraft to proceed only insofar as known air traffic is concerned.

Clearances shall contain positive (i.e. certain and doubtless) and concise data and shall, as far as practicable, be phrased in a standard manner.
Clearances shall contain the following in the order listed:
- Aircraft identification
- Clearance limit
- Route of flight
- Level(s) of flight for the entire route or part thereof and changes of levels if required
- Any necessary instructions or information on other matters

A clearance limit shall be described by specifying the name of the appropriate significant point, or aerodrome, or controlled airspace boundary.
For departing aircraft, the clearance limit will normally be the taxi-holding point of the runway in use.

When issuing a clearance covering a requested change in route or level, the exact nature of the change shall be included in the clearance.
When traffic conditions will not permit clearance of a requested change, the word "UNABLE" shall be used.
When an alternative route is offered and accepted by the flight crew, the amended clearance issued shall describe the route to the point where it joins the previously cleared route.

Change from instrument flight rules (IFR) flight to visual flight rules (VFR) flight is only acceptable when a message initiated by the pilot-in-command containing the specific expression "CANCELLING MY IFR FLIGHT" is received by an air traffic services unit.
No invitation to change from IFR flight to VFR flight is to be made either directly or by inference.

Departure restrictions, such as take-off and clearance expiry times, may be specified by the Tehran ACC when necessary.
The unit providing ATS for departure aircraft should be informed of any anticipated departure delays by Tehran ACC.

A standard and mandatory traffic orientation scheme (TOS) is published in I.R.Iran AIP to enable all aircraft operators to file flight plans as required.
Permission may be granted to a flight by an appropriate ATS authority to fly contrary to the published TOS.

Should any part of an airway or route be unavailable, aircraft shall be cleared to operate on alternative routes.

Unless a flight plan is filed via direct routing and an ATC clearance for it is obtained before departure, the subsequent requests of flight crew for bypassing the route angles shall require the controller's approval.
The approval of direct routing requests that affect other sectors or ATS units shall be withheld until the approval from those sectors or units is obtained.

Standard cruising levels are established in accordance with ICAO Annex 2.
Minimum levels, except when necessary for take-off or landing, shall be flown at a level that is not below the minimum flight level established or, where no such minimum flight level has been established, at a level which is at least 2500 feet above the highest obstacle located within 5 NM of the estimated position of the aircraft.

When delay is expected, Tehran ACC shall normally be responsible for clearing aircraft to a specified holding fix, and for including holding instructions and onward clearance time, as applicable.
Aircraft should normally be held at a designated holding point and other aircraft shall be separated vertically or laterally from the holding aircraft.
Levels at holding fixes shall be assigned in a manner that will facilitate clearing each aircraft to approach in its proper priority.### Speed Control
Indicated Airspeed (IAS): refers to the aircraft's speed as measured by the airspeed indicator
True Airspeed (TAS): the speed of an aircraft relative to the air mass it is in, regardless of air density
- Can be calculated from IAS or shown on FMS/GPS
- When expressed in knots, written as "KTAS"
Ground Speed (GS): TAS corrected for wind speed, represents speed relative to the ground
- Can be shown on FMS/GPS or calculated from TAS and wind direction/speed
Mach Number: TAS expressed as a fraction of the local speed of sound

General
- Instructed to adjust speed to facilitate safe and orderly traffic flow
- Flight crews should be given adequate notice of planned speed control
Methods of Application
- Speed control shall not be applied to aircraft in holding patterns
- Speed adjustments should be limited to necessary changes
- Instructions involving frequent changes of speed should be avoided
- Speed control may be applied using Mach number or IAS
Descending and Arriving Aircraft
- Authorized to absorb notified terminal delay by cruising at reduced speed
- May be instructed to maintain specific speeds during descent
- Speed reductions to less than 250 kt IAS during initial descent should be applied with flight crew concurrence

General
- Instructed to adjust rate of climb or descent to establish/maintain specific vertical separation minimum
- Vertical speed control may be applied between two climbing or two descending aircraft
Methods of Application
- Aircraft may be instructed to expedite climb/descent or maintain specific rate of climb/descent
- Controllers should ascertain aircraft performance characteristics and limitations
- Alternative methods of maintaining separation should be applied in a timely manner if required

Request for Visual Approach
- Clearance shall be withheld until approval is obtained from controlled aerodromes or coordination is made with uncontrolled ones