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 two systems used to collect this type of information:

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.

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 which operators must complete as a part of the State RVSM approval process -- provided that the requirements for AGHME use are satisfied.