The Gulf of America Grid System — AIM 10-1-4 Explained

AIM Text

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 America. This navigational route structure is completely independent 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.govunder 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 follows:
  1. 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.
  2. Each column in a set is named after its position, i.e., left (L), center (C), and right (R).
  3. 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 America 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 International (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 America. 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:
  1. The helicopter must be equipped for IFR operations and equipped with IFR approved GPS navigational units.
  2. The operator must obtain prior written approval from the appropriate Flight Standards District Office through a Letter of Authorization or Operations Specification, as appropriate.
  3. The operator must be a signatory to the Houston ARTCC Letter of Agreement.
4. Operators who wish to benefit from ADS-B based ATC separation services must meet the following additional requirements:
  1. The Operator's installed ADS-B Out equipment must meet the performance requirements of one of the following FAA Technical Standard Orders (TSO), or later revisions: TSO-C154c, Universal Access Transceiver (UAT) Automatic Dependent Surveillance-Broadcast (ADS-B) Equipment, or TSO-C166b, Extended Squitter Automatic Dependent Surveillance-Broadcast (ADS-B) and Traffic Information.
  2. Flight crews must comply with the procedures prescribed in the Houston ARTCC Letter of Agreement dated December 17, 2009, or later.
    
    NOTE-
    The unique ADS-B architecture in the Gulf of America depends upon reception of an aircraft's Mode C in addition to the other message elements described in 14 CFR 91.227. Flight crews must be made aware that loss of Mode C also means that ATC will not receive the aircraft's ADS-B signal.
5. FAA/AIS publishes the grid system waypoints on the IFR Gulf of America Vertical Flight Reference Chart. A commercial equivalent is also available. The chart is updated annually and is available from an FAA approved print provider or FAA directly, website address: http://www.faa.gov/air_traffic/flight_info/aeronav.

Source: FAA Aeronautical Information Manual · current edition · paragraph 10-1-4.

The short answer

This AIM section describes the FAA’s Gulf of America IFR Grid System — advisory guidance on a navigational route structure, independent of ground-based NAVAIDs, that supports offshore helicopter IFR operations. It explains the grid’s 300-plus waypoints spaced 20 minutes apart, the five-letter naming convention, ADS-B-based ATC separation, and the requirements operators must meet to file IFR flight plans using the grid.

Research Notes

Common Questions

How are the Gulf of America grid waypoints spaced and named?

The Grid System is defined by over 300 offshore waypoints located 20 minutes apart in latitude and longitude. Five-letter names encode position: a three-letter identifier for a geographic area or NAVAID to the north, a column letter (L, C, or R), and a row lettered alphabetically north to south. For example, LCHRC is “Lake Charles Romeo Charlie.”

What does an operator need to file IFR flight plans using the Gulf grid?

Three requirements apply: the helicopter must be equipped for IFR with IFR-approved GPS navigation units; the operator must obtain prior written approval from the appropriate Flight Standards District Office via a Letter of Authorization or Operations Specification; and the operator must be a signatory to the Houston ARTCC Letter of Agreement.

What ADS-B equipment is needed for ATC separation services in the Gulf grid?

Installed ADS-B Out equipment must meet the performance requirements of TSO-C154c (UAT ADS-B) or TSO-C166b (Extended Squitter ADS-B), or later revisions, and crews must comply with the Houston ARTCC Letter of Agreement. The architecture depends on reception of the aircraft’s Mode C in addition to the elements in 14 CFR 91.227.

10-1-4. The Gulf of America Grid System