4-7-1. Introduction and Background

a. Introduction. On 20 October 2011 at 0900
UTC, the Federal Aviation Administration (FAA),
Serviciós a la Navegacion en el Espacio Aéreo
Mexicano (SENEAM) and the Direccion General de
Aeronautica Civil (DGAC) Mexico implemented 50
Nautical Mile (NM) lateral separation between
aircraft authorized Required Navigation Perform-
ance 10 (RNP 10) or RNP 4 operating in the Gulf of
Mexico (GoMex) Oceanic Control Areas (CTA).
Existing Air Traffic Services (ATS) routes and route
operating policies did not change for this implement-
ation.

b. RNP 10 Versus RNAV 10 Terminology. "RNP
10" has the same meaning and application as "RNAV
10". The ICAO Performance-based Navigation

(PBN) Manual (ICAO Doc 9613), Volume II, Part B,

Chapter 1 (Implementing RNAV 10, Designated and

Authorized as RNP 10) explains that the term "RNP

10" was in use before the publication of the ICAO

PBN Manual and the manual has "grandfathered in"
its continued use when implementing an "RNAV 10"
navigation specification.

c. Background. 50 NM lateral separation was
first applied between aircraft authorized for RNP 10
operations on the North Pacific Route System in
April 1998. Since that time, 50 NM lateral separation
has been expanded throughout the Pacific Flight
Information Regions (FIRs) and is currently applied
in other airspaces, including, starting in June 2008,
the West Atlantic Route System. GoMex 50 NM
lateral separation implementation will apply the
experience gained in those operations.

d. Control Areas (CTA) Affected. 50 NM lateral
separation is implemented in the following CTAs/
FIRs/Upper Control Areas (UTA).

1 The Houston Oceanic CTA/FIR and the
Gulf of Mexico portion of the Miami Oceanic
CTA/FIR.
(a) The Monterrey CTA and Merida High
CTA within the Mexico FIR/UTA

e. Reference Material. Information useful for
flight planning and operations within the Gulf of
Mexico under this 50 NM lateral separation initiative
can be found in the West Atlantic Route System, Gulf
of Mexico, and Caribbean Resource Guide for U.S.
Operators located at www.faa.gov/about/office_org/
headquarters_offices/avs/offices/afs/afs400/afs470/
media/WATRS.pdf. The Guide can also be found
through a web search for "WATRS, GOMEX,
Caribbean Resource Guide."

4-7-2. Lateral Separation Minima Applied

a. 50 NM lateral separation is applied in the
GoMex CTA's between aircraft authorized RNP 10 or
RNP 4 at all altitudes above the floor of controlled
airspace.

b. The current lateral separation minima of 100

NM in the Houston, Monterrey and Merida CTAs,

and 90 NM in the Miami Oceanic CTA will continues

to be applied between aircraft not authorized RNP 10

or RNP 4.

4-7-3. Operation on Routes on the
Periphery of the Gulf of Mexico CTAs
Operations on certain routes that fall within the
boundaries of affected CTAs are not affected by the
introduction of 50 NM lateral separation. Operation
on the following routes is not affected:

a. Routes that are flown by reference to ICAO
standard ground-based navigation aids (VOR,
VOR/DME, NDB).
b. Special Area Navigation (RNAV) routes Q100,
Q102 and Q105 in the Houston, Jacksonville and
Miami CTAs.

4-7-4. Provisions for Non-RNP 10 Aircraft
(Not Authorized RNP 10 or RNP 4)
a. Operators of aircraft not authorized RNP 10 (or
RNP 4) must annotate their ICAO flight plan for Gulf
of Mexico operations as follows:
Item 18: "STS/NON-RNP10" (no space between
letters and numbers).