The EUR RMA operates 3 Height Monitoring Units in Europe which capture all aircraft within their respective coverage areas at RVSM levels. These systems employ very sensitive multi lateration techniques to measure the 3 dimensional positions of aircraft to within a few metres accuracy. Height monitoring software developed by EUROCONTROL then measures deviations from valid RVSM flight levels and estimates the aircraft Altimetry System Error (ASE) using advanced processing techniques including corrections for variations in meteorological pressure levels.

In addition to the mechanism employing the HMUs height monitoring can also be conducted using a GPS Monitoring Unit (GMU).

The EUR RMA is also active in developing alternative means of monitoring aircraft height keeping performance using aircraft ADS-B transmissions processed through a modified form of EUROCONTROL height monitoring software.

Height Monitoring Unit

An HMU is a ground based system consisting of two main components - HME (Height Monitoring Element) and TMU (Total vertical error Monitoring Unit).

The HME captures SSR transponder signals from aircraft replying to interrogations from radar stations. The signals contain the information from Mode S and Mode A/C transmissions. The HME determines the geometric height and position of an aircraft by comparing the time of reception of the SSR transponder signals at different receiver locations. This information is transmitted to the TMU as one plot per second. The data is collated by the TMU to create a track history of the aircraft passing through the area of coverage. The track information is then combined with meteorological data to evaluate the overall value for Total Vertical Error (TVE).

When completed, the monitoring process produces TVE (Total Vertical Error), AAD (Assigned Altitude Deviation) and ASE (Altimeter System Error) readings for each aircraft measured. In the European context, Height Monitoring results are automatically transmitted to the EUR RMA at EUROCONTROL Headquarters, Brussels where they are verified and credited to approved aircraft and operators.

EUR Region HMU Locations

The three European Height Monitoring Systems are deployed at the following locations;

• Geneva in Switzerland - 46°21’49”N….005°55’34”E (near GVA VOR)
• Linz in Austria - 48°12’08”N....014°17’35”E (near LNZ VOR)
• Nattenheim in Germany - 49°56’45”N….006°33’25”E (near NTM VOR)

The coverage of each HMU has a radius of 45 NM.

GPS Monitoring Unit

The GPS Monitoring Unit (GMU) is a carry-on system placed on an aircraft for a single flight. Its main advantage is the ability to monitor an individual aircraft during normal operations without the need to fly in a particular portion of airspace, with the exception that operations must be conducted in ECAC airspace. Data files from a GMU have to be post processed in order to extract height keeping performance data. After processing, the RMA will credit the results to the operator/airframe.

GMU operations are conducted by ARINC UK and there is a charge for the service.  To arrange a GMU flight please contact ARIC UK's GMU team.

Monitoring in other regions

There are currently 3 recognised height monitoring methodologies in operation around the world. Ground based Height Monitoring Systems, GMU and ASE estimation from ADS-B data.

Ground based height monitoring systems are in operation in the Europe, the US and Japan. GMU monitoring is conducted globally and systems based on ADS-B data are currently operational in the US, Australia, China and the Asian RVSM region.

Further details on these other monitoring programmes can be found here.