1. CHARACTERISTICS OF THE AIRSPACE.

a. General. The airspace above and surrounding the Gulf of Mexico is complex and includes heavy concentrations of multi-altitude military operations, high altitude air carrier operations, and low altitude helicopter activity. There are numerous alert, warning, noise sensitive, and restricted areas; control zones; heavy concentrations of student pilot activity; and areas of communication and navigation unreliability. As the volume of air traffic in this area has increased, it has become more common for flights to deviate from track, fail to make position reports, or report an incorrect position. Separation of air traffic is a matter of increasing concern in this airspace because of this increased activity. Any operation that is conducted in international airspace on an instrument flight rules (IFR) flight plan, a visual flight rules (VFR) controlled flight plan, or at night and that continues beyond the published range of normal airways navigation facilities (nondirectional radio beacon (NDB), very high frequency (VHF) omnidirectional radio range (VOR)/distance measuring equipment (DME)) is considered to be a long range navigation operation. Long range navigation in a control area (CTA) requires that the aircraft be navigated to the degree of accuracy required for the control of air traffic; that is, the aircraft should remain within one-half of the lateral separation standard from the centerline of the assigned track. The aircraft should also remain within the established longitudinal and vertical separation standards for the area of operation. These

separation standards can be found in the international Civil Aviation Organization (ICAO) Regional Supplementary Procedures Document 7030/2. For flights conducted within international airspace under U.S. jurisdiction, Federal Aviation Administration (FAA) Order 7110.83, "Oceanic Air Traffic Control Handbook" provides a simplified version of these separation standards. Federal Aviation Regulations (FAR) 91.703(a) requires that civil aircraft must comply with ICAO Annex 2 when operating over the high seas. Annex 2 requires that "aircraft shall be equipped with suitable instruments and with navigation equipment appropriate to the route being flown." In addition, Annex 6, Part H stipulates that an airplane operated in international airspace be provided with navigation equipment that will enable it to proceed in accordance with the flight plan and the requirements of the air traffic services. Annex 2 further requires that an aircraft shall adhere to the "current flight plan unless a request for change has been made and clearance received from the appropriate air traffic control (ATC) facility. "

b. Control of Air Traffic. ATC of the airspace over the Gulf of Mexico is assigned to the Houston Air Route Traffic Control Center (ARTCC). This center controls airspace within and outside of the U.S. Air Defense Identification Zone (ADIZ). The Houston CTA/Flight Information Region (FIR) includes the airspace in the northern part of the Gulf of Mexico. This control extends southward from Houston Center's coastal CTA to the middle of the Gulf in the vicinity of longitude N 24 30'. The Houston CTA/FIR borders Houston's coastal control in the west and north, and meets Miami's oceanic CTA/FIR at latitude W 86 in the east. The southern border of the Houston CTA/FIR is under the control of several Mexican FIR/upper control areas (UTA) and is controlled by Havana CTA in the southeast. Flight operations in this area must be conducted in accordance with the applicable FAR and ICAO Annex 2, "Rules of the Air." The navigation and communication equipment required for operations over the high seas must be installed and fully operational for flight in this airspace.

c. Flight Plans. Unless otherwise authorized by ATC, no aircraft may be operated in oceanic airspace unless a flight plan has been filed. VFR operations in oceanic airspace are permitted only between sunrise and sunset at or below flight level (FL) 180. Although VFR flights are permitted in offshore airspace (the airspace between the U.S. 12-mile limit and the oceanic control area (OCA)/FIR boundary), instrument meteorological conditions (IMC) are commonly encountered. It is recommended that pilots hold an instrument rating, the aircraft be equipped for IFR flight, and that an IFR flight plan be filed.

d. Alert Areas. Alert areas are areas wherein a large volume of pilot training flights or unusual aeronautical activity is contained. All activity within alert areas must be conducted according to the FAR, without waiver, and no activity that may be hazardous to other aircraft may be conducted. All aircraft within an alert area, both participating and nonparticipating, are equally responsible for collision avoidance.

e. Controlled Firing Areas. Controlled firing areas contain activities such as the firing of missiles and rockets, ordnance disposal, and static testing of large rocket motors. The users of these areas are responsible for immediate suspension of activities in the event that the activity might endanger nonparticipating aircraft. The controlled firing area locations in the Gulf of Mexico are published in Notices to Airmen (NOTAM).

f. Key West International Airport. FAR Part 121 operations that land or depart from Key West International Airport must meet the special airport requirements of FAR 121.445.

g. Noise Sensitive Areas. Noise sensitive areas include outdoor assemblies of persons, churches, hospitals, schools, nursing homes, designated residential areas, and national park areas. As national park areas, wildlife refuges are considered noise sensitive areas. Numerous wildlife refuges are located along the U.S. coastline surrounding the Gulf of Mexico, and many of these refuges have large bird populations. The heaviest concentrations of these refuges are along the Texas and Florida coasts. VFR flights over noise sensitive areas should be no lower than 2,000 feet above the surface, weather permitting, even if flight at a lower altitude is otherwise permitted under FAR 91.119. The surface is defined as the highest terrain within 2,000 feet laterally of the route of flight, or the uppermost rim of a canyon or valley.

h. Warning Areas. Warning areas are established in international airspace and contain operations hazardous to nonparticipating aircraft. IFR clearances through this airspace can be issued when hazardous operations are not taking place. Because there is no provision in international agreements for prohibiting flights in international airspace, there is no restriction on flights in these areas. However, pilots should take note of the location of all warning areas along a planned route.

i. Restricted Areas. Restricted areas are designated under FAR Part 73 to contain activities considered hazardous to nonparticipating aircraft. Aircraft may not operate within 3 nautical miles (NM) of a restricted area unless authorized under the provisions of FAR 73.13. There are numerous restricted areas near and along the Gulf of Mexico coastline. Pilots should be aware of these areas and plan flights accordingly.

2. NAVIGATION AND COMMUNICATIONS IN THE GULF OF MEXICO.

a. Background. ICAO Annex 6, Part H contains standards and recommended practices adopted as the minimum standards for all airplanes engaged in general aviation international air navigation. It requires those aircraft operated in accordance with IFR, at night, or on a VFR controlled flights (such as in CTA/ FIR oceanic airspace) to have installed and approved radio communications equipment capable of conducting two-way communication at any time with the appropriate aeronautical stations on the prescribed frequencies.

b. High Frequency (HF) and VHF Communications. Due to the inherent "line of sight" limitations of VHF radio equipment used for international oceanic airspace communications, aircraft operating on an IFR or controlled VFR flight plan beyond VHF communications capability are required to maintain a continuous listening watch and communications capability on the assigned HF frequencies. Although these frequencies will be assign ed by ATC, actual communication will be with general purpose communication facilities such as an international flight service station (FSS) or Aeronautical Radio Inc. (ARINC). These facilities will be responsible for the relay of position reports and other information between the aircraft and ATC. Except in an emergency, the use of relay on VHF through aircraft operating at higher altitudes is not an acceptable method of communication with ATC.

c. Communication and Position Reporting. The following describes an area in the Houston CTA/ FIR where direct air traffic communication is not available:

N27°28' W086°00' to N27°30' W087°42' to
N25°50' W088°15' to N25°37' W091°55' to
N24°40' W093°19' to N24°28' W088°01' to
N24°00' W086°00' to beginning point.

Pilots planning flights through this area should be aware of the communications and position reporting requirements. HF communications are available for all oceanic flights, and limited VHF coverage is also available on 130.7 megahertz (MHz). The communication requirements for IFR flights within the Houston OCA are as follows:

(1) The aircraft must have functioning two-way radio communications equipment capable of communicating with at least one ground station from any point on the route.

(2) The crew must maintain a continuous listening watch on the appropriate frequency.

(3) All mandatory position reports must be made.

d. Position Reports. When flying an oceanic route in the Gulf of Mexico, position reports must be made over all designated reporting points. A position report must also be made upon crossing the FIR boundary. Unless otherwise required, reporting points should be located at intervals of 5 or 10 degrees latitude (if flying north/south) or longitude (if flying east/west) either north or south of the equator or east or west of the 180 degree meridian. Aircraft transversing 10 degrees of latitude or longitude in I hour, 20 minutes should normally report at 10 degree intervals. Slower aircraft should report at 5 degree intervals. In the absence of designated reporting points, position reports shall be made as instructed by ATC. Position reports are vital to air traffic safety and control. Inability to comply is a violation of the FAR and ICAO requirements.

e. Navigation Requirements. Class II navigation on routes in the Gulf of Mexico can be conducted using GPS, VOR/DME, and NDB supplemented by dead reckoning (DR). These routes are located offshore and are shown on enroute charts. The areas are established by FAA Order 7110.2C, "Procedures for Handling Airspace Matters," and serve aircraft operations between U.S. territorial limits, OCA/FIR boundaries, and/or domestic flights operating in part over the high seas. These transition CTA's permit ATC to apply domestic procedures and separation minimums. Because independent radar surveillance is maintained within these CTAs, separation minimums are not as large as for other OCAs. As long as radar surveillance is maintained, operations may be conducted on Gulf routes using VOR/DME and NDB supplemented by DR. The radar surveillance provides an equivalent level of safety even though DR may be required for extended periods. Because of the proximity of these routes to shore-based facilities, the accuracy of DR can be enhanced by the use of shore based navigational aids (navaids). The DR techniques and procedures must be approved as part of the air carrier operator's training program, and should include contingency training for weather avoidance and emergencies. Approval for use of a single long range navigation system on these routes, as well as the navigation techniques discussed in this paragraph, are part of the operations specifications issued to air carrier operators.

f. Use of NDB for Navigation. The use of NDB as a primary source of navigation on long range flights presents the operator with numerous limitations and restrictions inherent in low frequency radio equipment and the low frequency signals they receive. NDB navaids of the highest power (2,000 watts or greater) that are maintained and flight checked as suitable for navigation, are limited to a usable service and/or reception range of 75 NM from the facility at any altitude. Although the operator may be able to receive standard AM broadcast stations with NDB equipment, primary dependence on these facilities for navigation is a questionable operating practice. The following are some of the inherent problems associated with reception of these stations:

(1) Infrequent station identification.
(2) Foreign language station identification may be impossible without knowledge of the language.
(3) Transmitter sites are not always located with the studio facilities.
(4) Termination of service without notice.
(5) Weather or atmospheric disturbances may cause erratic and unreliable signal reception.
(6) Flight checks may not have been conducted to verify the suitability and reliability of the facility and signal for navigation.
(7) The "shoreline/mountain" effect may cause signal fluctuations.
(8) Standard broadcast stations are not dedicated for navigation purposes.

Considering these limitations, the operator should be able to navigate so as to maintain the course specified in the ATC clearance. The inadequacies of NDB as the sole source of navigation must be carefully evaluated, as an error of 10 degrees over 2,000 miles can result in a deviation of 350 miles.

3. INTERNATIONAL OPERATIONS.

a. Operations to Mexico. Pilots should be aware of the landing restrictions in effect at Mexico City Airport. A fee of 3.77 million pesos (approximately $ 1,240) will be imposed on aircraft that land or depart from this airport during peak hours (7:00 am - 10:00 am; 5:00 - 9:00 pm). If an aircraft lands during peak hours but departs during nonpeak hours, 75 percent of the fee will be imposed. Operators planning a flight to Mexico should check the NOTAMs for updated information. FAR Part 121 operations to Guadalajara, Mexico must meet FAR 121.445 special airport qualification requirements.

b. Operations to Cuba. FAR 121.445 requirements for special airport qualifications apply to FAR Part 121 operations landing or departing from Guantanamo Bay Naval Air Station. Operators should be aware that the Cuban government has issued a warning that Cuban Armed Forces will shoot down any aircraft that penetrates Cuban airspace without authorization and refuses to land for inspection.

4. MILITARY AND HELICOPTER OPERATIONS.

a. Military Operations Areas (MOA). Military operations represent approximately one third of the air traffic in the Gulf of Mexico. These operations include a high volume of nonhazardous training flights, which are contained within MOAs. MCIAs and military training routes (MTR) are shown on VFR and sectional maps. However, MTRs are subject to change every 56 days. Because the charts are only issued every 6 months, pilots are strongly advised to contact the nearest FSS for current route dimensions and status.

b. Helicopter Operations. Pilots should be aware of the nature and extent of helicopter operations within the Gulf of Mexico. The density of helicopter traffic is primarily due to the presence of numerous oil rigs and drilling platforms in the Gulf. The majority of these flights are below 2,000 feet mean sea level at varying distances from the coastline. Additional information on helicopter operations is contained in Chapter 9 of this advisory circular (AC).