Skip to page content
Official US Government Icon

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure Site Icon

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

The latest general information on the Coronavirus (COVID-19) is available on For FAA-specific COVID-19 resources, please visit
United States Department of TransportationUnited States Department of Transportation

Monitoring Methods

Monitoring aircraft height-keeping performance consists of collection of necessary data using specialized systems, estimation of relevant performance parameters and comparison of these parameter estimates to corresponding RVSM requirements, on both an individual-aircraft and a system-wide basis.

The objectives of monitoring are two:

  • To ensure that the height-keeping performance in RVSM airspace as a whole complies with system requirements supporting continued safe use of the RVSM
  • To ensure that individual operators and aircraft comply with applicable RVSM requirements, compliance which an operator must demonstrate in the course of obtaining State RVSM approval

As noted, the collection of necessary data is the first step in monitoring aircraft height-keeping performance. Aircraft geometric height is one of these data sources. There are three systems used to collect this type of information:

ADS-B Height Monitoring

New! Aircraft equipped with qualified ADS-B out systems are height-monitored each Monday during normal operations at RVSM altitudes when operating in airspace where sufficient ADS-B data is available to the FAA to determine RVSM performance. Aircraft that are due for periodic monitoring or that must verify performance can fly any Monday to obtain a monitoring result.

Operators who elect to utilize Part 91 Appendix G, section 9 to access RVSM airspace must verify their altitude-keeping performance. The current list of aircraft and their most recent successful monitoring date can be found at RVSM Approvals in the file labeled US IGA Operators with Domestic RVSM Authorization under Part 91 Section 9 (ADS-B).

Please allow 2-4 weeks for processing and posting of updated data.

US operators that are not listed, or do not have a current monitoring date in any of the monitoring result files can request ADS-B results by providing flight details using the ADS-B Monitoring Request form (PDF).

Aircraft Geometric Height Measurement Element (AGHME)

The FAA Technical Center has developed the ground-based Aircraft Geometric Height Measurement Element (AGHME) system as the principal means of satisfying the first objective (at top of page) of monitoring in connection with the North American RVSM. These systems are positioned at fixed locations in the United States and Canada, automatically producing estimates of the geometric height of suitably equipped aircraft flying within the coverage area of an AGHME constellation.

Although intended to examine aggregate height-keeping performance, the AGHME system is entirely suited for the individual-aircraft monitoring for operators that are not eligible for ADS-B monitoring.

GPS-based Monitoring Unit (GMU)

The GMU is a special-purpose data collection system carried aboard an aircraft for one flight, during which the unit collects Global Positioning System pseudoranges. Post-flight processing of these data ensures estimates of aircraft geometric height which are of sufficient accuracy to permit estimation of relevant height-keeping performance parameters. In parallel, the current-generation FAA GMU also collects secondary surveillance radar Mode C data, which also contributes to parameter estimation.

The GMU has been in use since 1996 and has used by thousands of operators to satisfy monitoring requirements associated with the State RVSM approval process, thus supporting satisfaction of the second objective of monitoring noted above. However, the ensemble of monitoring results produced by application of the GMU has also been used to satisfy the first objective.

** A LOA or Operations Specifications must be obtained prior to conducting a monitoring flight.

Page last modified: