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AIM 

6/17/21 

than that published in the procedure, until canceling 
IFR. 

(c) 

IFR obstruction clearance areas are not 

applied to the VFR segment between the MAP and 
the landing site. Obstacle or terrain avoidance from 
the MAP to the landing site is the responsibility of the 
pilot. 

(d) 

Upon reaching the MAP defined on the 

approach procedure, or as soon as practicable after 
reaching the MAP, the pilot advises ATC whether 
proceeding VFR and canceling IFR, or complying 
with the missed approach instructions. See para-
graph 5

1

15, Canceling IFR Flight Plan. 

(e) 

If the visual segment penetrates Class B, 

C, or D airspace, pilots are responsible for obtaining 
a Special VFR clearance, when required. 

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4.  The Gulf of Mexico Grid System 

a. 

On October 8, 1998, the Southwest Regional 

Office of the FAA, with assistance from the 
Helicopter Safety Advisory Conference (HSAC), 
implemented the world’s first Instrument Flight 
Rules (IFR) Grid System in the Gulf of Mexico. This 
navigational route structure is completely indepen-
dent of ground

based navigation aids (NAVAIDs) 

and was designed to facilitate helicopter IFR 
operations to offshore destinations. The Grid System 
is defined by over 300 offshore waypoints located 20 
minutes apart (latitude and longitude). Flight plan 
routes are routinely defined by just 4 segments: 
departure point (lat/long), first en route grid 
waypoint, last en route grid waypoint prior to 
approach procedure, and destination point (lat/long). 
There are over 4,000 possible offshore landing sites. 
Upon reaching the waypoint prior to the destination, 
the pilot may execute an Offshore Standard Approach 
Procedure (OSAP), a Helicopter En Route Descent 
Areas (HEDA) approach, or an Airborne Radar 
Approach (ARA). For more information on these 
helicopter instrument procedures, refer to FAA AC 
90

80B,  Approval of Offshore Standard Approach 

Procedures, Airborne Radar Approaches, and 
Helicopter En Route Descent Areas, on the FAA 
website 

http://www.faa.gov 

under Advisory Circu-

lars. The return flight plan is just the reverse with the 
requested stand

alone GPS approach contained in the 

remarks section. 

1. 

The large number (over 300) of waypoints in 

the grid system makes it difficult to assign 
phonetically pronounceable names to the waypoints 
that would be meaningful to pilots and controllers. A 
unique naming system was adopted that enables 
pilots and controllers to derive the fix position from 
the name. The five

letter names are derived as 

follows: 

(a) 

The waypoints are divided into sets of 

3 columns each. A three

letter identifier, identifying 

a geographical area or a NAVAID to the north, 
represents each set. 

(b) 

Each column in a set is named after its 

position, i.e., left (L), center (C), and right (R). 

(c) 

The rows of the grid are named 

alphabetically from north to south, starting with A for 
the northern most row. 

EXAMPLE

 

LCHRC would be pronounced “Lake Charles Romeo 
Charlie.” The waypoint is in the right

hand column of the 

Lake Charles VOR set, in row C (third south from the 
northern most row). 

2. 

In December 2009, significant improvements 

to the Gulf of Mexico grid system were realized with 
the introduction of ATC separation services using 
ADS

B. In cooperation with the oil and gas services 

industry, HSAC and Helicopter Association Interna-
tional (HAI), the FAA installed an infrastructure of 
ADS

B ground stations, weather stations (AWOS) 

and VHF remote communication outlets (RCO) 
throughout a large area of the Gulf of Mexico. This 
infrastructure allows the FAA’s Houston ARTCC to 
provide “domestic

like” air traffic control service in 

the offshore area beyond 12nm from the coastline to 
hundreds of miles offshore to aircraft equipped with 
ADS

B. Properly equipped aircraft can now be 

authorized to receive more direct routing, domestic 
en route separation minima and real time flight 
following. Operators who do not have authorization 
to receive ATC separation services using ADS

B, 

will continue to use the low altitude grid system and 
receive procedural separation from Houston ARTCC. 
Non

ADS

B equipped aircraft also benefit from 

improved VHF communication and expanded 
weather information coverage. 

3. 

Three requirements must be met for operators 

to file IFR flight plans utilizing the grid: 

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Helicopter IFR Operations