RVSM is one of the few areas of continuing airworthiness where something outside your organisation independently checks whether your work is holding up. RVSM height monitoring measures how accurately aircraft actually keep their assigned levels, and the results arrive whether or not anyone in the hangar asked for them. Treat it as the scorecard for the maintenance programme, because in practice that is what it is.

Who monitors, and from where

In Europe the function sits with the EUR Regional Monitoring Agency, operated by EUROCONTROL. Its EUR RMA service page names one fixed unit: the European Height Monitoring Unit is deployed at Nattenheim in Germany.

That is worth stating plainly, because older material — including some training packages still in circulation — lists two or three stations. The network has been rationalised. EUROCONTROL’s guidelines, Edition 4.0 of 19 November 2024, record that the station at Linz has been withdrawn from service permanently. If your procedures, exposition or internal training slides still name Linz, or name a station at Geneva, they are out of date. Nattenheim is the unit EUROCONTROL names.

ICAO Doc 9574 sits in the background as the document describing the responsibilities of the authorities involved in the RVSM monitoring process. It is not the source of any threshold or interval, and it is regularly miscited as though it were.

The three numbers

SPA.RVSM.115 of Regulation (EU) No 965/2012 names three quantities and attaches a reporting threshold to each. In our own words, for an engineering audience: total vertical error is the gap between where the aircraft was cleared to be and where it geometrically was; altimetry system error is the part of that gap contributed by the altimetry system itself — the part your maintenance programme exists to contain; and assigned altitude deviation is how far the aircraft sat from its cleared level as its own systems saw it.

The rule text is precise about the duty. The operator shall report recorded or communicated occurrences of height-keeping errors caused by malfunction of aircraft equipment or of operational nature, equal to or greater than a total vertical error of ±90 m (±300 ft), an altimetry system error of ±75 m (±245 ft), or an assigned altitude deviation of ±90 m (±300 ft). Reports go to the competent authority within 72 hours and shall include an initial analysis of causal factors and measures taken to prevent repeat occurrences. Where height-keeping errors are recorded or received, the operator shall take immediate action to rectify the conditions that caused the errors and provide follow-up reports if the competent authority requests them.

Note who reports: the operator. Not the CAMO, not the Part-145 organisation. But read the second sentence again — an initial analysis of causal factors, within 72 hours. When altimetry system error is the number that has moved, the causal analysis is a maintenance investigation, and it will be run by the people who understand the static system, the airframe geometry and the autopilot. The operator signs it. Continuing airworthiness writes it.

Certification criteria and the reporting trigger are not the same thing

This is the most common technical error in circulation on the subject, and it is worth killing off. ±75 m (±245 ft) is not a certification limit. It is not “the full-envelope ceiling of the ASE budget”. It is an operational reporting trigger applied to an individual aircraft.

There is no 75 m or 245 ft figure anywhere in CS ACNS.E.RVSM.035. The two instruments answer different questions: one asks whether a type may be certified for RVSM, on a statistical basis across a group; the other asks whether one aircraft, on one occasion, has produced an error the authority needs to know about. An aircraft can sit well inside the reporting trigger and still be performing far worse than the type was certified to achieve — which is exactly the situation a good CAMO wants to notice before the airspace does.

The statistical work behind the certification numbers is also not yours. CS-ACNS Appendix B provides that, for aircraft being manufactured, every Nth aircraft will be inspected in detail and every Mth aircraft will be flight test calibrated, where N and M are determined by the aircraft constructor and agreed to by the competent authority. Group mean-plus-three-standard-deviations tracking is a manufacturing activity.

How often monitoring happens — and where that comes from

Nowhere in the regulation. This surprises people. AMC1 SPA.RVSM.105(g) asks an applicant only for a plan for participation in any applicable verification or monitoring programme acceptable to the competent authority, described as a check on a sample of the operator’s fleet by a regional monitoring agency’s independent height-monitoring system. It states no interval and no number of airframes.

The numbers come from EUROCONTROL’s RVSM Monitoring Groups and Minimum Monitoring Requirements, version 2026.1 of 2 June 2026, which provides that operators of aircraft types contained in the relevant category shall have a minimum of 2 airframes monitored every 2 years or 1,000 flight hours, whichever is longer. Three features of that sentence matter and are routinely misstated:

• It is an operator obligation, not a CAMO one — though the CAMO is normally the party that knows which airframes are available and when.
• It applies per monitoring group, to a minimum of 2 airframes. It is not a per-aircraft interval, and treating it as one produces a compliance plan that is both wrong and expensive.
• The same document attributes the long-term minimum monitoring requirements to Annex 6 to the Convention on International Civil Aviation — not to Doc 9574.

In our experience the practical consequence is a scheduling conversation the CAMO should own even though the duty is the operator’s: which monitoring group does each type fall into, which airframes will be offered, and when. That belongs in a procedure, and our guidance on how to write a CAME and on structuring a CAMO management system shows where a monitoring-participation and error-reporting interface sits alongside your occurrence reporting process.

What to do when a report lands

A height-keeping report is not a piece of operations paperwork that happens to mention the aircraft. It is a 72-hour engineering deadline. The questions are familiar to anyone who has read the underlying continuing-airworthiness expectations: has any repair or alteration affected airframe surface and airflow near a static source, and was a geometry check performed? Has the static system been disturbed and leak-checked? Is the autopilot inspection programme current? Is the RVSM equipment being maintained to the component manufacturers’ instructions and the performance criteria of the RVSM approval data package?

Those four questions are, almost always, where the answer is. The geometry side is covered in skin waviness, static ports and the hidden geometry of RVSM; the failure chain in full is walked through in the static-port repair that costs an aircraft; and what should have been scheduled in the first place is in what the CAMO must build into the RVSM maintenance programme. For the underlying argument, see why RVSM is a maintenance problem, not just an operations one, and for structured training, our RVSM maintenance training for CAMO and Part-145 personnel course.

Frequently asked questions