HMU — Ground Based Height Monitoring Units


          A HMU (Height Monitoring Unit) is a ground based height monitoring system. The HMU uses multilateration information.

The HMU measures Altimetry System Error for any airframe (no specific requirements to equipment of aircraft) which performs gorizontal flight inside the RVSM airspace (290 to 410 flight level) and inside the HMU range area during 120 seconds.

In RMA Eurasia region HMU uses ADS-B(AHMS) data in order to verify ASE measurements, this technique is called Dual-monitoring system. As a result, operators can obtain the most proven ASE measurements.


ADS-B Based Height Monitoring System (AHMS)


An AHMS is aground-based height keeping performance monitoring system that uses geometric height data available from automatic dependant surveillance-broadcast (ADS-B) equipped aircraft in order to calculate the Altimetry System Error (ASE). Operators wishing to use the system are only required to hold an RVSM approval and be equipped with an ADS-B DO-260B (version 2). Monitoring in airspace where a wide-area ADS-B network is available will not require an aircraft to specifically overfly any specific AHMS site as rutine flight operations can be monitored on a continuous basis with no operational impact.

Like other ground-based systems, AHMS provides large volumes of data and permit repeated measurements on individual airframes, which helps RMAs better assess the height keeping performance of airframes over time and discover undesirable trends and patterns.

In addition, RMA EURASIA AHMSes can recognize Large High Deviations (over 90 m) from assigned flight level inside its range.


RMA EURASIA HMU/AHMS Locations and status

Velikie Luki HMU coverage area -Out of service from 01.04.2024

Velikie Luki AHMS coverage area -Operational

Khabarovsk HMU coverage area - Out of service from 01.09.2022

Khabarovsk AHMS coverage area -Operational


EUR Region HMU Locations

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)
Geneva in Switzerland - 46°21’49”N….005°55’34”E (near GVA VOR)


You can check HMUs status here


NATCMA Region HMU Location

Strumble in Scotland – is located near Strumble (STU) VOR below the centerline of UL9 (formerly UG1).  The horizontal coverage area for the HMU is a 13.8 nm radius circle centered on position N51 56 00’ W004 40’ 00


To check the HMU status contact UK NATS at


JASMA Region HMU Location

Setouchi in Japan – 343044N 1341627E. Setouchi HMU coverage is 40 nm.


You can check HMUs status here


NAARMO Region AGHME (Aircraft Geometric Height Measurement Element) Locations

Atlantic City, Wichita, Cleveland, and Phoenix (United States);

Ottawa and Lethbridge (Canada).


You can check AGHMEs status here


AAMA Region ADS-B (Automatic Dependent Surveillance Broadcast) Location




HMU radius of operation are usually 45 nm.