Height Keeping Performance Monitoring Systems

In relation to Height Keeping Performance Monitoring (HKPM) requirements, monitoring data from any regional monitoring programme established in accordance with Annex 11,, maybe used to satisfy the requirement.

Monitoring height keeping performance is to estimate and evaluate the Altimetry System Error (ASE) of an aircraft operating in the RVSM airspace. The ASE is the difference between the altitude which the pilot, ground controller, and aircraft systems believe aircraft to be at and the actual altitude (click for more information on ASE). To be compliant with international standards, the ASE of an aircraft must be less than 245 ft (75 m). The number of aircraft required to be monitored is specified in Asia/Pacific RVSM Minimum Monitoring Requirements (MMR).

There are two main types of monitoring systems available today.

1. In-Flight GPS-Based Monitoring Systems

This type of service requires an engineer to install a portable GPS-based monitoring unit, known as GMU or EGMU, on a targeted aircraft for a single flight. Its main advantage is the ability to monitor an individual aircraft during normal operations without the need to fly over a ground-based monitoring system in a particular portion of airspace. MAAR is currently providing this service (see HKPM Usign EGMU for more information). For other providers, please see each individual RMA website.

2. Ground-Based Height Monitoring Systems

Ground-based monitoring units are stationary stations installed at fixed locations. These systems can compute Altimetry System Error (ASE) for all aircraft flying over their operational coverages. Ground-based systems can give repetitive measurements over a period of time, which allow RMAs to discover undesirable patterns or trends. There are 3 subtypes of ground-based monitoring systems available today:

How to Obtain Monitoring Results

  • Monitoring results from all RMAs are shared before the 15th of each month. These results are then correlated with the RVSM approval records (based on ICAO 24-bit address or aircraft registration) and published on our website (the last 3 columns of our RVSM approval records) at least once a month.
  • For operators from States under MAAR's responsibility, if you wish MAAR to issue an official letter to your State CAA containing the monitoring results obtained from our AHMS or from other RMAs, please complete and submit Monitoring Result Retrieval Form to maar@aerothai.co.th.
  • For operators from States under MAAR's responsibility, a summary report of ASE measured by our AHMS for each operator's fleet is available on a per-request basis. Operators who wish to obtain such reports can e-mail your request to maar@aerothai.co.th with the subject line: "Requesting ASE Report for <3-letter ICAO operator code>". MAAR processes the data monthly, and the report is typically available by the 15th of the month following the last month of data.
  • For operators from States that are not under MAAR's responsibility who wish to obtain ASE results, please contact your respective RMA. Please note that the availability of calculated values of ASE depends on each RMA's policy.
  • Please note that ASE numerical values from different types of monitoring systems are derived differently and may have different measurement errors. For example, ASE values from MAAR's AHMS are computed by averaging the repeated measurements over a period of time, which tend to have less error than the single measurement from a GMU. However, data collected from our EGMU will be post-processed using differential-GPS technique in order to reduce GPS error.