AMC1 ACNS.D.EHS.015 Data transmission

ED Decision 2013/031/R

(a)     The EHS capability compliance verification should address all the Mode S transponder registers that are indicated as available in the Mode S Specific Services Capability reports (registers). The compliance verification should include a list of transponder registers supported by the installation, including the parameters that are available in each register. The list should contain the registers that are indicated as available in the Mode Specific Capability reports (18₁₆ to 1C₁₆), except the following registers:

(1)     registers managed by the transponder to support the Mode S airborne initiated protocol (02₁₆, 03₁₆, 04₁₆);

(2)     registers containing extended squitters information (05₁₆, 06₁₆, 07₁₆, 08₁₆, 09₁₆, 0A₁₆);

(3)     aircraft capability reporting (10₁₆ to 1F₁₆);

(4)     Aircraft Identification (20₁₆);

(5)     ACAS RA report (30₁₆); and

(6)     transponder dependant information (5F₁₆, E3₁₆, E4₁₆, E7₁₆, EA₁₆).

Note 1: An example of a minimum list of registers to support EHS is provided in Subpart D Appendix C.

Note 2: An example of other registers and parameters is provided in Subpart D Appendix C.

(b)     Verification of operation

(1)     All the transponder registers containing data as defined in (a) should be verified to ensure correct data is transmitted by the Mode S transponder.

Note: Format and resolution of airborne parameters can be found in ED-73E Volume 2 or in ICAO Doc 9871 Edition 2.

(2)     Where a register is declared available but a parameter within that register is not available, it is necessary to verify that the status of the parameter is declared invalid in the corresponding aircraft register.

Note 1: Some parameters are particularly difficult to measure statically. To ensure that these parameters (e.g. Roll Angle, Track Angle Rate, Inertial Vertical Velocity) are correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the correct transponder register is transmitted (by the transponder), that the value of the parameter status bit is valid (status bit = 1), and the value of the parameter field is set to zero when aircraft is not moving on the ground. Alternatively, for such parameters which remain invalid in static condition, ground test may use simulation if simulated data bus signal meets sensor data bus specifications, the same data bus provides at least one other valid parameter which is tested and sensor specifications clearly establish availability conditions and format of the simulated data parameter.

Note 2: Due to the limitations of the static tests, a recommended option is to perform a flight and record the content of the different transponder registers (as extracted by a Mode S ground station) to verify that all parameters listed in (a) are changing in accordance with pilot input and aircraft attitude and manoeuvre.

Note 3: To minimise the certification effort for transponder follow-on installations, the applicant may claim from the responsible authority credit for applicable certification and test data obtained from equivalent aircraft installations. This is acceptable for a parameter only if all related equipment connected to the transponders are of the same type and same software revision number.

(c)      Aircraft parameters

(1)               Selected Altitude

(i)      MCP/FCU Selected Altitude

         Selected level input to the MCP or FCU should be used.

         In case there is no MCP/FCU Selected Altitude function, it is accepted to use the information provided by an altitude alerter.

(ii)     FMS Selected Altitude

         When available, it is recommended that the FMS Selected altitude field is provided.

         Note: This will allow the reporting of the intermediate selected altitudes during applications (e.g. Continuous Descent Operations) when the FMS provides the guidance input to the auto-pilot.

(iii)     MCP/FCU mode bits

         When data is available, it is recommended (optional) to provide information on autopilot mode which is selected by the flight crew.

         Note: It is accepted to set this bit to zero rather than providing wrong information.

(iv)     Target Altitude source bits

         The target altitude source bits are used to indicate the source (e.g. FCU/MCP, FMS) which provides the next level at which the aircraft will level off. This is also referred to as the Target Altitude. However, the necessary data may be inconsistent or not accessible. In this case, the status of target altitude source bits should indicate no source information provided (set to zero).

         Note: It is also acceptable that status of target altitude source bits is set to valid and target altitude source is set to 00 to indicate unknown.

(2)     Vertical Rate

         The Barometric Altitude Rate should contain value solely derived from barometric measurement.

         When different sources are available, the Inertial Vertical Velocity should contain data coming from the most accurate and steady source.

         Note 1: The vertical rate can be provided in the Barometric Altitude Rate and/or the Inertial Vertical Velocity fields of register 6016. Both the Barometric Altitude Rate and the Inertial Vertical Velocity can be transmitted simultaneously.

         Note 2: The Barometric Altitude Rate is usually very unsteady.

         Note 3: The Inertial Vertical Velocity (derived from IRS, AHRS and/or GPS) information is more filtered and smoothed.

(3)     Barometric Pressure Setting

If operating with reference to the standard pressure setting, the Barometric Pressure Setting field should indicate standard pressure value equivalent to 1.01325 10⁵ Pa.

(4)     Track Angle Rate or True Airspeed

If Track Angle Rate data cannot be readily provided due to the aircraft configuration, True Airspeed data should be substituted.

(5)     Roll Angle

It is difficult to test different values of Roll Angle when the aircraft is on the ground. To ensure that this parameter is correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the Roll Angle field in register 50₁₆ contains a credible value, consistent with aircraft roll angle on the ground, and the Roll Angle Status bit indicates valid data.

(6)     True Track Angle

It is difficult to test different values of True Track Angle when the aircraft is on the ground. To ensure that this parameter is correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the True Track Angle field in register 50₁₆ contains a value and the True Track Angle Status bit indicates valid data.

(7)     Ground Speed

It is difficult to test different values of Ground Speed when the aircraft is on the ground. To ensure that this parameter is correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the Ground Speed field in register 50₁₆ contains a value, consistent with the speed of the aircraft on the ground (close to zero if the aircraft is not moving) and the Ground Speed Status bit indicates valid data.

(8)     Magnetic Heading

To ensure that this parameter is correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the Magnetic Heading field in register 60₁₆ contains a value, consistent with the magnetic heading of the aircraft, and the Magnetic Heading Status bit indicates valid data.

(9)     Indicated Airspeed or Mach No

Indicated Airspeed and Mach No are considered as a single parameter. Both should be provided where available.

To ensure that these parameters are correctly received from the sensor and transmitted by the transponder, it is acceptable to test that the Indicated Airspeed or Mach fields in register 60₁₆ contain a value, consistent with the indicated airspeed or Mach No generated via a test set, and the Indicated Airspeed or Mach Status bits indicate valid data.

(d)     Sensor Sources

Particular attention should be given to the interface between data sources and transponders when multiple transponders and multiple sensors are employed. In this context, ‘sensors’ refers to FMS, IRS, AHRS, ADS, GPS, or Data Concentrator (or other) systems used to provide data to the transponder.

The crew should be aware, at all times, which sensors are providing information to the active transponder.

In an installation, where automatic sensor selection for the active transponder is not provided, the captain’s side transponder should utilise the captain’s side sensors, and the co-pilot’s side transponder should utilise the co-pilot’s side sensors.

Data parameters from different sensors of the same type should not be mixed.

Note: For example, Mode-C or Mode-S altitude reporting information from ADC source #1 should not be mixed with reporting of TAS, Baro Vertical Rate, Mach from ADC source #2. In this case, partially blocking of data output from either ADC source #1 or #2 will cause uncorrelated results. This could result in problems with ATC ground processing of the data.

Where only single sensors are available (i.e. single FMS), it is permissible to connect the single sensor to multiple transponders. It should be noted that this may result in reduced operational availability should the single sensor fail.