Crossing the Gulf Of Mexico (GOMEX)
A number of years ago, the FAA and Mexico's SENEAM redesigned the airway structure across the Gulf Of Mexico (GOMEX). Part of this redesign was driven by the need to be able to handle more traffic across the GOMEX. Given that aircraft are out of RADAR contact over the GOMEX, increased aircraft separation was required to ensure adequate safety. The answer was to replace most of the legacy "colored routes" with new RNAV routes that require RNP-10 Letters Of Authorization (LOAs). Here is where the fun began.

To fly the L(Lima) and M (Mike) routes across the GOMEX, you must have A1 in your RNP codes. In order to do this, you must have a LOA issued to you by the Civil Aviation authority of your country of registry. For most of us, that is the FAA. In order to accommodate NON-RNP10 aircraft, the FAA and SENEAM left A770/UA770 and A766/UA766 (Amber Routes) across the GOMEX. Therefore, it is preferred that NON-RNP10 aircraft flight plan for these two airways and not the Lima or Mike routes. However, we still get many requests from pilots who prefer to fly the Lima and Mike routes even though they are NON-RNP10.

IT IS possible for a NON-RNP10 aircraft to fly the Lima and Mike routes by filing a flight plan with RMK/NON-RNP10 in Box 18 of their ICAO Flight Plan. However, ATC will need to verify that the additional separation required does not interfere with other aircraft. If it does, then the NON-RNP10 aircraft may be assigned a different altitude from that requested to avoid any conflicts. This altitude may be above FL400 or below FL300 which have significant operational consequences. Therefore, we recommend that pilots plan their routes using the Amber Routes for fuel planning purposes. Then you can either file the Lima or Mike routes and if you are assigned an unacceptable altitude, you can request to be re-routed along the Amber Routes. Or, you can file your flight plan route using the Amber Routes and then when airborne, you can request to be re-routed along a Lima or Mike route if a satisfactory altitude is available.