The one-thousand-foot idea.

Reduced Vertical Separation Minimum, or RVSM, is one of the most successful capacity measures in aviation history. Above flight level two-nine-zero, controllers used to keep two thousand feet of vertical space between aircraft. RVSM halves that to one thousand feet — three hundred metres — between flight level two-nine-zero and flight level four-one-zero, inclusive. That single change roughly doubled the number of usable cruising levels in the busiest, most fuel-efficient part of the sky. European RVSM airspace has operated this way since January two thousand and two. Now hold that number in your mind: one thousand feet. That is the entire safety margin between two airliners closing at a combined speed of well over a thousand knots. The system only works because every aircraft in it keeps its altitude with extraordinary precision. And precision is not bought once at certification — it is maintained. That is where you come in.

The chain of approval. 

Let me place you in the regulatory picture, because RVSM confuses people who think it is purely an operational topic. The international foundation is ICAO Document 9574, the manual for a three-hundred-metre vertical separation minimum. The airworthiness criteria — how an aircraft proves it can hold height accurately enough — now sit in the EASA Certification Specification CS-ACNS, in Subpart E, Section 2, on Reduced Vertical Separation Minimum. If you trained on this topic some years ago you will know these criteria as JAA Temporary Guidance Leaflet Number 6 — TGL 6. That leaflet has been superseded: its airworthiness criteria moved into CS-ACNS, and its continuing-airworthiness and maintenance items are now captured in the Acceptable Means of Compliance AMC1 ACNS.A.GEN.010, paragraph (b). The substance is the same discipline; the reference has simply moved to the EASA framework. On top of that sits the operator’s approval. Under Regulation (EU) 965/2012, Part-SPA, an operator needs a specific RVSM approval before it can fly in RVSM airspace. The operational-approval requirements sit in SPA.RVSM.105, and the equipment the aircraft must carry is set out in SPA.RVSM.110, RVSM equipment requirements. Read those together and you find something important: that operational approval is conditional on the aircraft holding airworthiness approval and on there being a continuing-airworthiness and maintenance programme that keeps it valid. And this is the part that lands on us — the continuing-airworthiness and maintenance expectations for RVSM are spelled out in the Acceptable Means of Compliance AMC3 SPA.RVSM.105, which is where much of the old TGL 6 maintenance content now lives. We will refer back to it throughout this course.

Why it lands on your desk. 

That last condition is your mandate. Under Regulation (EU) 1321/2014, the CAMO — or CAO — owns the aircraft maintenance programme, and the Part-145 organisation carries out the work. One point to be clear about from the outset: CS-ACNS is a certification specification. You, as CAMO or Part-145, do not show compliance against the CS directly — that is the job of a Part-21 design organisation, which must satisfy CS-ACNS whenever the aircraft is designed, modified or repaired. So why does this course spend time inside the CS at all? Because you cannot connect the dots without it. Knowing what CS-ACNS requires of the altimetry systems and the airframe geometry is what tells you which condition you are preserving, and — crucially — when a change or repair has stepped outside the approved data and must be referred to a Part-21 organisation working to the CS. The CS sets the baseline; your job is to keep the aircraft on it and to recognise when only a Part-21 design review can put it back. RVSM is not a one-time tick at certification. The requirement is explicit: the integrity of the design features that keep the altimetry system accurate must be verified by scheduled tests and inspections within an approved maintenance programme. Think about what actually degrades height-keeping. A static port that sits a fraction of a millimetre proud after a repair. A skin panel near that port that is slightly wavy. A small leak in a static line that was not checked after a disconnect. An altitude-hold function that has drifted. None of those are the operator’s doing. Every one of them is owned by continuing airworthiness and maintenance. So when an aircraft loses RVSM approval, it is rarely the crew that caused it and rarely the crew that can fix it. It is us. Over the next half hour we will walk through exactly what the CAMO must build into the programme, what Part-145 must do on the floor, and what happens when a monitoring unit flags an aircraft that is no longer holding its level.