4/20/23 

AIM 

5. 

When no delay is expected, the controller should issue a clearance beyond the fix as soon as possible and, 

whenever possible, at least 5 minutes before the aircraft reaches the clearance limit. 

6. 

Pilots should report to ATC the time and altitude/flight level at which the aircraft reaches the clearance 

limit and report leaving the clearance limit. 

NOTE

−

 

In the event of two

−

way communications failure, pilots are required to comply with 14 CFR Section 91.185. 

4

−

4

−

4.  Amended Clearances 

a. 

Amendments to the initial clearance will be issued at any time an air traffic controller deems such action 

necessary to avoid possible confliction between aircraft. Clearances will require that a flight “hold” or change 

altitude prior to reaching the point where standard separation from other IFR traffic would no longer exist. 

NOTE

−

 

Some pilots have questioned this action and requested “traffic information” and were at a loss when the reply indicated “no 

traffic report.” In such cases the controller has taken action to prevent a traffic confliction which would have occurred at 

a distant point. 

b. 

A pilot may wish an explanation of the handling of the flight at the time of occurrence; however, controllers 

are not able to take time from their immediate control duties nor can they afford to overload the ATC 

communications channels to furnish explanations. Pilots may obtain an explanation by directing a letter or 

telephone call to the chief controller of the facility involved. 

c. 

Pilots have the privilege of requesting a different clearance from that which has been issued by ATC if they 

feel that they have information which would make another course of action more practicable or if aircraft 

equipment limitations or company procedures forbid compliance with the clearance issued. 

4

−

4

−

5.  Coded Departure Route (CDR) 

a. 

CDRs provide air traffic control a rapid means to reroute departing aircraft when the filed route is 

constrained by either weather or congestion. 

b. 

CDRs consist of an eight

−

character designator that represents a route of flight. The first three alphanumeric 

characters represent the departure airport, characters four through six represent the arrival airport, and the last 

two characters are chosen by the overlying ARTCC. For example, PITORDN1 is an alternate route from 

Pittsburgh to Chicago. Participating aircrews may then be re

−

cleared by air traffic control via the CDR 

abbreviated clearance, PITORDN1. 

c. 

CDRs are updated on the 56 day charting cycle. Participating aircrews must ensure that their CDR is current. 

d. 

Traditionally, CDRs have been used by air transport companies that have signed a Memorandum of 

Agreement with the local air traffic control facility. General aviation customers who wish to participate in the 

program may now enter “CDR Capable” in the remarks section of their flight plan. 

e. 

When “CDR Capable” is entered into the remarks section of the flight plan the general aviation customer 

communicates to ATC the ability to decode the current CDR into a flight plan route and the willingness to fly 

a different route than that which was filed. 

4

−

4

−

6.  Special VFR Clearances 

a. 

An ATC clearance must be obtained 

prior

 to operating within a Class B, Class C, Class D, or Class E surface 

area when the weather is less than that required for VFR flight. A VFR pilot may request and be given a clearance 

to enter, leave, or operate within most Class D and Class E surface areas and some Class B and Class C surface 

areas in special VFR conditions, traffic permitting, and providing such flight will not delay IFR operations. All 

special VFR flights must remain clear of clouds. The visibility requirements for special VFR aircraft (other than 

helicopters) are: 

ATC Clearances and Aircraft Separation 

4

−

4

−

3