Understanding RVSM Height Monitoring Requirements

If you fly in RVSM airspace, RVSM height monitoring is required regardless of whether you hold an RVSM LOA (B046 under Part 91 Appendix G, Section 3) or are operating in US domestic airspace without an LOA via ADSB-OUT (Part 91 Appendix G, Section 9).

Safe vertical separation in RVSM airspace relies on strict altitude-keeping performance of all aircraft. Altimetry System Error (ASE) represents the difference between the pressure altitude indicated to the flightcrew and the aircraft’s actual free stream pressure altitude, and it forms a key component of Total Vertical Error (TVE).

Importantly, this data is not visible to pilots, as it does not appear on cockpit altitude displays, nor is it transmitted by transponder data used by ATC. As a result, ASE remains undetectable to flightcrews, routine air traffic control monitoring, and onboard collision avoidance systems such as TCAS, underscoring the importance of independent height monitoring programs in ensuring RVSM compliance.

The lesson is - you have no idea whether your aircraft system is operating within RVSM tolerances by looking at your altimeters. This can only be verified by height monitoring.

Initial Height Monitoring: Getting Started

If your aircraft has not previously completed RVSM monitoring, an initial monitoring flight must be accomplished within six months of receiving your RVSM authorization (RVSM B046 LOA). Or if you're operating without an LOA under Part 91 Section 9 (ADSB OUT), an initial height monitoring flight must be completed within six months of the date you took over operational control. Usually this is the date you took delivery of the aircraft.

Unlike an RVSM LOA, RVSM height monitoring flights are transferrable from operator to operator. If you purchase a preowned aircraft, and a height monitoring flight was already completed by the prior operator within the last 24 months or 1,000 flight hours, you can proceed to Ongoing Monitoring Requirements below.

Ongoing Monitoring Requirements

Operators with and without RVSM LOAs are required to complete recurrent monitoring flights at intervals of:

• 24 calendar months, or

• 1,000 flight hours, whichever is longer

  • Flight hours must be calculated by subtracting the hours currently on the plane from the number of hours that were on the plane on the date of the last monitoring flight. If this number is over 1,000 flight hours, and it's been longer than 24 months from the last monitoring date, you need to complete a recurrent monitoring flight.

ADS-B: Passive Monitoring

Fortunately, if you're flying in RVSM airspace in both the United States and Canada, height monitoring can be completed without any prior coordination. As long as your aircraft has a compliant ADS-B OUT system, you will be passively monitored while flying in RVSM airspace at any RVSM altitude (FL290-410 inclusive). When sufficient surveillance data is available, the FAA (or authorized monitoring agency) can assess altitude-keeping performance without requiring a dedicated monitoring flight.

This most likely means you have met the monitoring requirement simply by flying routinely in RVSM airspace—provided the ADS-B Out system is functioning properly.

Tracking Compliance

The NAARMO (North American Approvals Registry and Monitoring Organization) maintains a database of the RVSM airworthiness, operational approval (LOAs), and height monitoring status for commercial and general aviation operators in the United States, Canada and Mexico.

You can access NAARMO databases to verify whether your aircraft has been monitored or is due for monitoring.

NAARMO monitored aircraft databases are available here:

• https://www.faa.gov/air_traffic/separation_standards/naarmo/rvsm_approvals

• NOTE: The approvals database Section 9 lists all monitored Part 91 aircraft without an RVSM LOA and approvals database Section 3 lists all monitored aircraft with an RVSM authorization (Part 91 LOA or Part 135 OpSpec). Be sure to check the correct database applicable to your operation!

Additional information on available monitoring methods (ADSB, GMU) is available here:

• https://www.faa.gov/air_traffic/separation_standards/naarmo/monitoring_methods/

If your Aircraft Doesn't Appear in the NAARMO Monitoring Results Database

If you've frequently flown in RVSM airspace in the United States or Canada and your aircraft does not show up in either NAARMO monitoring results databases, you can contact the NAARMO by submitting a General Inquiry Form to naarmo@faa.gov. Visit the website below for more information:

NAARMO Points of Contact | Federal Aviation Administration

When a Dedicated Monitoring Flight Is Needed

If monitoring has not been successfully completed within the required interval, a dedicated height monitoring flight may be necessary.

For operators based outside the United States, monitoring is typically accomplished by:

• Overflying a Height Monitoring Unit (HMU) (commonly used in Europe), or

• Conducting a GPS-based Monitoring Unit (GMU) flight with a qualified technician

These methods provide the data needed to validate RVSM performance when ADS-B monitoring is not available.

The Importance of Tracking Height Keeping Performance Issues

Altitude-keeping errors fall into two broad categories: 1) errors caused by malfunction of aircraft equipment, and 2) operational errors due to pilot training and/or procedural compliance.

If you are notified of an altitude deviation by the FAA, you must address the root cause and implement corrective actions immediately. If the root cause is related to pilot training or operational procedures, the corrective action could be completing additional training or updating your RVSM operations manual. If the root cause is a malfunction of aircraft equipment, additional maintenance/inspections are required.

The most common culprit of altitude-keeping errors is related to issues with the aircraft skin around the static ports/pitot probes (paint chips/cracks/dents, variations in paint thickness, or modifications to the airframe that effect airflow). Skin waviness inspections are often not required by aircraft OEMs at scheduled intervals. Check your Aircraft Maintenance Manual to confirm. As part of your standard operating procedures, you should include a check to visually inspect the aircraft skin around the static port and pitot probes frequently to identify any potential issues before they result in an altitude error.

Passing a Monitoring Flight

If your aircraft passed a monitoring flight, meaning the altitude error is within tolerances of AC91-85B, you will not be contacted by anyone. Your aircraft N number and serial number will appear in one of the NAARMO databases along with a date of most recent monitoring. No further action is required!

You may want to take a screenshot of the NAARMO database and store that on your device along with the RVSM manual and authorizations (if issued). Jot down the number of hours on the aircraft as well. This may be helpful in the event of a ramp check.

Failing a Monitoring Flight

If you fail a monitoring flight, you will be contacted by your local FAA office (FSDO or IFO) - depending on the extent of the error. If the error is extreme enough, your aircraft may be prohibited from flying in RVSM airspace until the issue is resolved. Corrective action must be documented before you're allowed to enter RVSM airspace again.

Per AC91-86B, errors which should be reported and investigated by the FAA are: Total Vertical Error (TVE) equal to or greater than ±300 ft (±90 m), altimetry system error (ASE) equal to or greater than ±245 ft (±75 m), and assigned altitude deviation (AAD) equal to or greater than ±300 ft (±90 m).

Final Thoughts

RVSM height monitoring is a continuous process, not a one-time requirement. With the widespread use of ADS-B Out, compliance has become more streamlined—but it still requires action to maintain safety.