We're starting with MNPSA — that stands for Minimum Navigation Performance… — Page 126, Lesson 197

I want to walk you through the North Atlantic airspace structure and the equipment requirements for flying in it. We're starting with MNPSA — that stands for Minimum Navigation Performance Specification Airspace. Let me give you the exact vertical boundaries first. MNPS Airspace extends from Flight Level 285 up to Flight Level 420. That's FL 285 to FL 420. Now, within that band, we also have RVSM airspace — Reduced Vertical Separation Minimum — which occupies FL 290 through FL 410. So the RVSM band sits inside the larger MNPSA band. If you're flying in MNPSA, you must also be authorized to fly in RVSM airspace, and you must comply with the altimetry MASPS — that's the Minimum Aircraft System Performance Specification for altimetry. Now, let's talk about how RVSM flight levels are assigned. In domestic airspace — that is, non-oceanic airspace — RVSM flight levels are allocated according to your magnetic track. If you're flying Easterly, you get odd flight levels: 290, 310, 330, and so on. If you're flying Westerly, you get even flight levels: 300, 320, 340, and so on. But here's the key difference over the North Atlantic: because the majority of traffic flows in a tidal pattern — meaning most flights go one direction during one part of the day and the opposite direction later — the Organized Track System, or OTS, is used. During OTS operations, all flight levels are available in both directions. Outside the OTS, standard RVSM flight level allocation applies, meaning you go back to the odd/Easterly, even/Westerly rule. Let me now walk you through the minimum equipment requirements for RVSM flight. You need: - Two independent barometric altimeters that agree with each other to within plus or minus 200 feet. - An autopilot with height hold capability. - An altitude deviation alerting system — at minimum, an aural alert that activates if the aircraft deviates by plus or minus 300 feet from its assigned altitude. - An SSR — Secondary Surveillance Radar — with altitude reporting mode, which is Mode C. - And before you enter the NAT Oceanic Control Area, the altimeters must be checked. During flight, you must report to ATS when you reach any new cruising level. And if a deviation of more than 300 feet occurs, you must report it immediately to Air Traffic Services, and then submit a written report after the flight. Now let's move to navigation system requirements for MNPS Airspace. The minimum equipment is two independent Long Range Navigation Systems, or LRNS. The reason for two is to cover the failure of one system. The approved systems that qualify as LRNS are: - GNSS — Global Navigation Satellite System, which includes GPS - INS — Inertial Navigation System - IRS — Inertial Reference System Each of these systems must be capable of providing continuous position, track, and speed information. That's the performance standard. Additionally, all turbine-powered aeroplanes with a maximum take-off mass greater than 5,700 kilograms, or having more than 19 passenger seats, are required to carry and operate ACAS II in the NAT region. ACAS II is Airborne Collision Avoidance System, version II. The excerpt notes that this equipment is already required for relevant aircraft of all EU operators anyway, so it's not an additional burden for most operators. Now let's talk about navigation system serviceability. The requirement for two LRNS covers the case of a failure in one system. Each system must have a failure warning indication so you know when one has failed. If you have a triple INS installation used as an IRS — that's three inertial systems — a 'voting' system is employed. The voting system compares the outputs of all three and selects the most accurate information, effectively isolating a failed unit. In a double INS system — just two units — you don't have that voting capability. If a failure occurs, you'll need external information, specifically heading and drift data, to determine which system is inaccurate. If you experience a total failure of all navigation systems, the excerpt gives you two options: ask another aircraft for assistance, or follow the contrails of other traffic. But if it's a total navigation system failure, you must declare an emergency using MAYDAY or PAN PAN procedures. The specific navigation system failure procedures are covered later in this chapter, so we'll get to those in due course.