These OCAs are contiguous—meaning they touch each other without gaps — Page 126, Lesson 194

I want to walk you through the North Atlantic airspace structure and the rules for flying within the Minimum Navigation Performance Specification Airspace, or MNPSA. Let's start with the Oceanic Control Areas, or OCAs. We have four main OCAs in the North Atlantic: Shanwick, Gander, New York, and Reykjavik. These OCAs are contiguous—meaning they touch each other without gaps. The east-west boundaries between them are set at specific lines of longitude. The boundary between Shanwick and Gander is at 30 degrees west. The boundary between Santa Maria and New York is at 40 degrees west. The north-south boundary between these pairs is at 45 degrees north latitude. So Shanwick and Gander share a boundary at 30W, and Santa Maria and New York share one at 40W, with the line at 45N separating the northern pair from the southern pair. Reykjavik OCA is different. It extends from the northern boundaries of Shanwick and Gander all the way up to the North Pole, and it includes most of Greenland. The eastern and western continental boundaries of these OCAs are defined by domestic airspace—that is, the national Flight Information Regions, or FIRs. But here's an important detail: beyond the southwest boundary of New York's North Atlantic Oceanic Airspace, the airspace is still New York OCA, but it is not part of the NAT MNPSA. This area is called the West Atlantic Route System, abbreviated WATRS. It contains routings for traffic between the USA and the Caribbean. Also, the eastern boundary of Reykjavik OCA is the western boundary of the Bodø OCA—pronounced "Boo der"—which is in Norway. Bodø OCA is not part of the MNPSA area either. Now, let's talk about MNPS Authority. Operators of aircraft flying within the MNPSA are required to have authority approval, which is stated on their Air Operator Certificate, or AOC. This approval requires the aircraft to be able to navigate in accordance with the relevant Required Navigation Performance, or RNP. When an operator has MNPS approval, they indicate this to Air Traffic Control by inserting the letters "SX" in item 10 of the flight plan. Next, I want to explain a key operational practice for turbojet aircraft in the MNPSA. Practical experience has shown that when two or more turbojet aircraft are operating along the same route at the same flight level and maintain the same Mach number, they are more likely to maintain a constant time interval between each other than when using other methods. Why? Because these aircraft are normally subject to approximately the same wind and air temperature conditions. Minor variations in ground speed that might increase or decrease the spacing between them tend to be neutralized over long periods of flight. So, the requested TRUE Mach number—taking into account known errors in the flight deck indication—is to be inserted in item 15 of the flight plan. Wherever possible, Air Traffic Control will accommodate this requested speed. However, occasionally ATC may need to assign a Mach number that is 0.01 higher than requested, or 0.02 lower than requested. Pilots should maintain their last assigned Mach number during step-climbs in oceanic airspace. If, due to aircraft performance, maintaining that Mach number during a step-climb is not feasible, then ATC should be advised at the time of the request for the step climb. After leaving oceanic airspace, pilots must continue to maintain their assigned Mach number in domestic controlled airspace unless and until the appropriate ATC unit authorizes a change.