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AIM 

6/17/21 

leaving the outer marker or fix used in lieu of the outer 
marker inbound on final approach (precision 
approach). 

(b) 

A corrected estimate at anytime it 

becomes apparent that an estimate as previously 
submitted is in error in excess of 2 minutes. For 
flights in the North Atlantic (NAT), a revised 
estimate is required if the error is 3 minutes or more. 

b. 

Pilots encountering weather conditions which 

have not been forecast, or hazardous conditions 
which have been forecast, are expected to forward a 
report of such weather to ATC. 

REFERENCE

 

AIM, Para 7

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18, Pilot Weather Reports (PIREPs). 

14 CFR Section 91.183(B) and (C). 

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4.  Airways and Route Systems 

a. 

Three fixed route systems are established for air 

navigation purposes. They are the Federal airway 
system (consisting of VOR and L/MF routes), the jet 
route system, and the RNAV route system. To the 
extent possible, these route systems are aligned in an 
overlying manner to facilitate transition between 
each. 

1. 

The VOR and L/MF (nondirectional radio 

beacons) Airway System consists of airways 
designated from 1,200 feet above the surface (or in 
some instances higher) up to but not including 18,000 
feet MSL. These airways are depicted on IFR Enroute 
Low Altitude Charts. 

NOTE

 

The altitude limits of a victor airway should not be 
exceeded except to effect transition within or between route 
structures. 

(a) 

Except in Alaska, the VOR airways are: 

predicated solely on VOR or VORTAC navigation 
aids; depicted in black on aeronautical charts; and 
identified by a “V” (Victor) followed by the airway 
number (for example, V12). 

NOTE

 

Segments of VOR airways in Alaska are based on L/MF 
navigation aids and charted in brown instead of black on 
en route charts. 

(1) 

A segment of an airway which is 

common to two or more routes carries the numbers of 
all the airways which coincide for that segment. 
When such is the case, pilots filing a flight plan need 
to indicate only that airway number for the route filed. 

NOTE

 

A pilot who intends to make an airway flight, using VOR 
facilities, will simply specify the appropriate “victor” 
airway(s) in the flight plan. For example, if a flight is to be 
made from Chicago to New Orleans at 8,000 feet, using 
omniranges only, the route may be indicated as “departing 
from Chicago

Midway, cruising 8,000 feet via Victor 9 to 

Moisant International.” If flight is to be conducted in part 
by means of L/MF navigation aids and in part on 
omniranges, specifications of the appropriate airways in 
the flight plan will indicate which types of facilities will be 
used along the described routes, and, for IFR flight, permit 
ATC to issue a traffic clearance accordingly. A route may 
also be described by specifying the station over which the 
flight will pass, but in this case since many VORs and L/MF 
aids have the same name, the pilot must be careful to 
indicate which aid will be used at a particular location. 
This will be indicated in the route of flight portion of the 
flight plan by specifying the type of facility to be used after 
the location name in the following manner: Newark L/MF, 
Allentown VOR. 

(2) 

With respect to position reporting, 

reporting points are designated for VOR Airway 
Systems. Flights using Victor Airways will report 
over these points unless advised otherwise by ATC. 

(b) 

The L/MF airways (colored airways) are 

predicated solely on L/MF navigation aids and are 
depicted in brown on aeronautical charts and are 
identified by color name and number (e.g., Amber 
One). Green and Red airways are plotted east and 
west. Amber and Blue airways are plotted north and 
south. 

NOTE

 

Except for G13 in North Carolina, the colored airway 
system exists only in the state of Alaska. All other such 
airways formerly so designated in the conterminous U.S. 
have been rescinded. 

(c) 

The use of TSO

C145 (as revised) or 

TSO

C146 (as revised) GPS/WAAS navigation 

systems is allowed in Alaska as the only means of 
navigation on published air traffic service (ATS) 
routes, including those Victor, T

Routes, and colored 

airway segments designated with a second minimum 
en route altitude (MEA) depicted in blue and 
followed by the letter G at those lower altitudes. The 
altitudes so depicted are below the minimum 
reception altitude (MRA) of the land

based 

navigation facility defining the route segment, and 
guarantee standard en route obstacle clearance and 
two

way communications. Air carrier operators 

requiring operations specifications are authorized to 

En Route Procedures 

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