They're the air traffic control authority for that oceanic sector — Page 141, Lesson 220

I want to walk you through the special contingencies and procedures for flying in the MNPSA — the Minimum Navigation Performance Specification Airspace. This is the North Atlantic airspace where the separation standards are very tight, so any deviation from normal operation has serious consequences. Let's start with the core warning: if you're flying in the MNPSA and you lose the ability to maintain your level, navigate accurately, or communicate, the results can be serious. At the very first indication that things are 'not normal', pilots are advised to communicate the problem to the OACC — that's the Oceanic Area Control Centre. They're the air traffic control authority for that oceanic sector. Now, if you lose HF communications — High Frequency radio — there's a workaround. You can ask an adjacent aircraft on VHF — Very High Frequency — to relay your message. This works because all aircraft flying in the MNPSA are required to monitor two specific VHF frequencies: 123.45 MHz and 121.5 MHz. 121.5 MHz is the international air distress frequency, and 123.45 MHz is the inter-pilot air-to-air frequency. If you have a pressurization failure, you'll need to descend rapidly to a safe altitude. When you do that, you are required to broadcast safety information on 121.5 MHz — specifically, you announce the altitudes you're passing through as you descend. That's called a safety broadcast. Now let's move to the Strategic Lateral Offset Procedure, abbreviated as SLOP. This procedure exists for one specific reason: if an aeroplane flying in the NAT MNPSA — North Atlantic MNPSA — encounters wake turbulence, and the pilot considers it necessary to move away from the turbulence, SLOP allows the aeroplane's track to be offset from the aeroplane causing the turbulence. SLOP offers three options. The first option is to fly along the cleared track centre line — that's your assigned route with no offset. The second option is to offset by 1 nautical mile to the right. The third option is to offset by 2 nautical miles to the right only. Notice that all offsets are to the right — never to the left. This keeps all aircraft moving in a consistent lateral direction relative to the track. Here's an important detail: if neither of those offset options puts you upwind of the other aeroplane — meaning you'd still be in the turbulence — then you should contact the other aeroplane on 123.45 MHz and request that they adopt an allowable alternate downwind SLOP offset. So you're asking them to move instead. If you do encounter wake turbulence while flying in NAT MNPS airspace, you must submit a report to the NAT Central Monitoring Agency. That's the body that collects data on airspace safety events. Now let's talk about deviation around severe weather. If your aircraft needs to deviate laterally from its track to avoid weather — for example, thunderstorms — the standard procedure is to request a revised clearance from ATC and obtain essential traffic information before you deviate. This applies even when you expect to deviate by a relatively small distance, say less than 10 nautical miles. You still ask first. However, there are contingency procedures for when you cannot obtain that prior revised ATC clearance. In that case, you should continue trying to get the clearance, but you also adopt the following steps. First, if possible, deviate away from the organized track or route system — meaning move away from the main flow of traffic. Second, establish communications with and alert nearby aircraft. You do this by broadcasting, at suitable intervals, your aircraft identification, your flight level, your aircraft position including the ATS route designator or the track code, and your intentions. You broadcast this on the frequency in use when it's VHF, and also on 121.5 MHz. As a back-up, you can use the VHF inter-pilot air-to-air frequency 123.45 MHz. Third, watch for conflicting traffic both visually — by looking out the window — and by reference to ACAS or TCAS if your aircraft is equipped. ACAS stands for Airborne Collision Avoidance System, and TCAS is Traffic Collision Avoidance System — they're the same concept, a system that alerts you to nearby traffic. Fourth, turn on all aircraft exterior lights. This makes your aircraft more visible to other pilots. Fifth, for deviations of less than 10 nautical miles, you should remain at the level assigned by ATC — don't change your altitude. Sixth, for deviations of greater than 10 nautical miles, when your aircraft is approximately 10 nautical miles from the track, you initiate a level change of plus or minus 300 feet. Whether you climb or descend depends on your direction of flight and the direction of the deviation. This 300-foot altitude change provides additional vertical separation from traffic on the original track. So to summarize: in the MNPSA, any loss of level, navigation, or communication is serious — communicate immediately. Use SLOP for wake turbulence with right offsets only. For weather deviations, request ATC clearance first, and if you can't get it, follow the contingency steps including broadcasting your position and intentions, watching for traffic, turning on lights, and adjusting altitude by 300 feet for deviations over 10 nautical miles.