ADS-B Monitoring System

        Background of ADS-B Monitoring Technology

        Based on the monitoring results from the ground-based monitoring system in the recent ten years, it is found that the height keeping performance (Altimetry System Error: ASE) of aircraft tend to deteriorate with the growth of flight time. And alsoASE can vary over the population of operational aircraft of the same type and withineach specific aircraft this error can vary with time in service.At the same time, the modification of aircraft and the damage of aircraft skin and pitot-static system during the flight canalso affect the height keeping performance. So It is of great importance to implement the long term height monitoring requirements.

        In recent years, with the rapid growth of fleet in China, China RMA has actively promoting ground-based height keeping performance monitoring system and master the core algorithm, and from 2012 with great help from AAMA and MAAR, the China RMA has established ADS-B monitoring system. This system can automatically monitor the aircraft position information and analyze aircraft Altimetry System Error (ASE) Stability.

       The China RMA is able to produce ADS-B monitoring results and the comparisonofresultswith AAMA and MAAR validate the effectiveness of the system.In the RASMAG/18 meeting, China RMA was endorsed to use ADS-B data for aircraft height keeping performance monitoring data calculation.

         The GeographicalCoverage of ADS-B Monitoring in China

         At present, the ADS-B monitoring system can cover most area in China. The coverage of ADS-B stations are showed in the picture below:

         ADS-B Monitoring Process

         Aircraft equipped with ADS-B Outcan be monitored automatically when flies over ADS-B stations. The monitoring data will be sent to the data processing center in Beijing through ADS-B data transfer network. China RMA will then obtain the aircraft’s ADS-B raw data and estimate HKP results through the HKP calculating system.

        The Issue of ADS-B Monitoring Report and ADS-B Monitoring Data Sharing

        China RMA calculates the HKP results based on ADS-B data and issue the monitoring report on a monthly basis:

        a.The Issue of ADS-B Monitoring Report:

        ♦ Aberrant or non-compliant aircraft: For aircraft under China RMA’s responsibility, China RMA will contact with related CAA authority and operator and send monitoring report to them; for other aircraft, China RMA will contact responsible RMA.

        ♦ Compliant aircraft: For aircraft under China RMA’s responsibility, China RMA will send monitoring report for every fleet to operator and relative authority quarterly. For other aircraft, China RMA will contact responsible RMA欧尼.

        b.ADS-B Data Share

        According to ICAO’s requirement, the ADS-B monitoring results are not provided directly to the operators, onlyshared between RMAs. China RMA will upload the monitoring data to the RMA security website on a monthly basis. At the same time, operators outside China RMA’s responsibility can request the ADS-B monitoring data of theirfleet in Chinese RVSM airspace by contacting their responsible RMA.

        The Work Flow of ADS-B DataProcessing by the China RMA

        The data processing flow for ADS-B data consists of the following stages:

        1. ADS-B Raw Data Processing and ASE Calculation

       The geometric height of aircraft can be seen as real height by analyzing the ADS-B data. Through meteorological data interpolation andheight referenceconversion between geometric height and pressure height, the ADS-B monitoring system is able to produce preliminary ASE estimates. But these results still need further analysis to determine the geoid height reference (either height abovemean sea-level (MSL) or height above ellipsoid (HAE)).

        2. Geoid Height Reference

        An aircraft will transmit geometric height as either HAMSL or HAE, depending on the GPS receiver. However, it is often not known which of these geoid assumptions is being used prior to our analysis and it must be determined from the HKP monitoring data analysis. The picture below shows the difference of HAE and MSL (geoid contours) in Chinese airspace.

         The height keeping performance (ASE) is a property of aircraft. In general the correct measure of ASE will remainrelatively static while the incorrect measure will change as a flight moves across geoid contours. For instance, for HAE aircraft, the ASE based on HAE height reference remains relatively static, but the one based on MSL moves across geoid contours; and vice versa. Based on this method, the correct geoid height reference of an aircraft could be determined from statisticalapproach. The picture below shows the example of choosing geoid height reference. We can see that this aircraft’sheight reference is MSL.

         3.TraceAnalysis of Aircraft Height Keeping Performance

         China RMA provides analysis of ASE trace versus time for a typical airframe, a monitoring group or a fleet. The picture below shows the ASE trace of a typical airframe.


        4.ASEDistribution Fitting

        Some airframes give larger scatters in their ASE traces. This may be due to theairframe having split pitot systems China RMA provides ASE distribution fitting to reflect the different performance of pilot/co-pilot altimetry systems..

          5.Comprehensive Analysis of ASE

          China RMA provides a comprehensive analysis of ASE for a typical airframe, including the ASE trace chart versus time, the geoid height reference analysis, ASE Distribution Fitting and flight track map.