Aeronautical Information Manual (AIM), page 576

Index   575 -- Page 576 -- 577

than that published in the procedure, until canceling

(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
(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.

10-1-4. 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 web
site http://www.faa.gov under Advisory Circulars.
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
(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.

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:

10-1-6 Helicopter IFR Operations

Page 576 of the Aeronautical Information Manual (AIM.pdf)
AIM: Official Guide to Basic Flight Information and ATC Procedures

Index   575 -- Page 576 -- 577