Canadian Aviation Regulations (CARs) 2019-1
Content last revised: 2007/12/30
The performance of Air Traffic Control (ATC) transponders can be tested using either a bench check or portable test equipment and shall meet the standards of airworthiness requirements elaborated in relation to section 571.02 of the CARs and listed in paragraphs (a) through (k) of this appendix. The test required by paragraph (k) is a system integration test to verify the accuracy of the data transmitted by the system as a whole, and as such shall be conducted on the aircraft. In order to prevent interference with the Air Traffic Control Radar Beacon System (ATCRBS) and airborne aircraft equipped with TCAS, portable test equipment shall be used with the appropriate precautions and operated at a rate of 235 interrogations per second. An additional 3 decibel (dB) loss is allowed to compensate for antenna coupling errors during receiver sensitivity measurements conducted in accordance with subsection (c)(1) when using portable equipment.
(i) Interference prevention can be accomplished by antenna shielding, direct coupling of aircraft transponder antenna to test set, or the use of anechoic enclosures away from other aircraft or reflective obstructions.
(ii) For definition of classes of transponders refer to the US FAA's Technical Standard Order (TSO-C112) entitled "Air Traffic Control Radar Beacon System/Mode Select (ATCRBS/Mode S) Airborne Equipment".
(a) Radio Reply Frequency
(1) For all classes of ATCRBS transponders, interrogate the transponder and verify that the reply frequency is 1090 ±3 Megahertz (MHz).
(2) For 1B, 2B and 3B Mode S transponders, interrogate the transponder and verify that the reply frequency is 1090 ±3 MHz.
(3) For class 1B, 2B and 3B Mode S transponders that incorporate the optional 1090 ±1 MHz reply frequency, interrogate the transponder and verify that the reply frequency is correct.
(4) For class 1A, 2A, 3A, and 4 Mode S transponders, interrogate the transponder and verify that the reply frequency is 1090 ±1 Mhz.
(1) When class 1B and 2B ATCRBS transponders, or class 1B, 2B and 3B Mode S transponders are interrogated on Mode 3/A at an interrogation rate between 230 and 1,000 interrogations per second; or when class 1A and 2A ATCRBS transponders or class 1B, 2A, 3A and 4 Mode S transponders are interrogated at a rate between 230 and 1,200 Mode 3/A interrogations per second:
(i) Verify that the transponder does not respond to more than 1 percent of the interrogations when the amplitude of P2 pulse is equal to P1 pulse; and,
(ii) Verify that the transponder replies to at least 90 percent of the ATCRBS interrogations when the amplitude of the P2 pulse is 9 dB less than the P1 pulse. If the test is conducted with a radiated test signal, the interrogation rate shall be 235 ±5 interrogations per second unless a higher rate has been approved for the test equipment used at that location.
(c) Receiver Sensitivity
(1) Verify that for any class of ATCRBS transponder, the receiver minimum triggering level (MTL) of the system is - 73 ±4 dbm, or that for any class of Mode S transponder, the receiver MTL for Mode S format (P6 type) interrogations is -74 ±3 dbm by use of a test set that is:
(i) connected to the antenna end of the transmission line;
(ii) connected to the antenna terminal of the transponder with a correction for transmission line loss; or
(iii) utilising a radiated signal.
(2) Verify that the difference in Mode 3/A and Mode C receiver sensitivity does not exceed 1 dbm for either any class of ATCRBS transponder or any class of Mode S transponder.
(d) Radio Frequency (RF) Peak Output Power
The maximum transmitter power output measured at the terminal of the antenna corresponds to the standard specified in TSO-C74c and RTCA/DO-181C Document related to the Minimum Operational Performance Standards for air traffic control radar beacon system.
(1) Verify that the transponder RF output power is within specifications for the class of transponder. Apply the same conditions as described in paragraph (c)(1) above.
(i) For class 1A and 2A ATCRBS transponders, verify that the minimum RF peak output power is at least 21.0 dbw (125 watts).
(ii) For class 1B and 2B ATCRBS transponders, verify that the minimum RF peak output power is at least 18.5 dbw (70 watts).
(iii) For class 1A, 2A, 3A, 4 and class 1B, 2B and 3B Mode S transponders that include the optional high RF peak output power, verify that the minimum RF peak output power is at least 21.0 dbw (125 watts).
(iv) For class 1B, 2B and 3B Mode S transponders, verify that the minimum RF peak output power is at least 18.5 dbw (70 watts).
(v) For any class of ATCRBS or any class of Mode S transponders, verify that the maximum RF peak output power does not exceed 27.0 dbw (500 watts).
(e) Mode S Diversity Transmission Channel Isolation
The tests specified in paragraphs (e) through (j) apply exclusively to Mode S transponders.
For any class of Mode S transponder that incorporates diversity operation, verify that the RF peak output power transmitted from the selected antenna exceeds the power transmitted from the nonselected antenna by at least 20 dB.
(f) Mode S Address
Interrogate the Mode S transponder and verify that it replies only to its assigned address. Use the correct address and at least two incorrect addresses. The interrogations shall be made at a nominal rate of 50 interrogations per second.
(g) Mode S Formats
Interrogate the Mode S transponder with uplink formats (UF) for which it is equipped and verify that the replies are made in the correct format. Use the surveillance formats UF=4 and 5. Verify that the altitude reported in the replies to UF=4 are the same as that reported in a valid ATCRBS Mode C reply. Verify that the identity reported in the replies to UF=5 are the same as that reported in a valid ATCRBS Mode 3/A reply. If the transponder is so equipped, use the communications formats UF=20, 21 and 24.
(h) Mode S All-call Interrogations
Interrogate the Mode S transponder with the Mode S-only all-call format UF=11 and the ATCRBS/Mode S all-call formats (1.6 microsecond P4 pulse) and verify that the correct address and capability are reported in the replies (downlink format DF=11).
(i) ATCRBS-only All-call Interrogation
Interrogate the Mode S transponder with the ATCRBS-only all-call interrogation (0.8 microsecond P4 pulse) and verify that no reply is generated.
Verify that the Mode S transponder generates a correct squitter approximately once per second.
(k) Integration Test
(1) The integration of the automatic pressure altitude reporting and ATC transponder systems shall be inspected and tested in accordance with the following procedures:
(i) The altimeter shall be adjusted to a setting of 1013.2 millibars (29.92 inches of mercury) for altitudes from sea level to the maximum certified altitude of the aircraft,
(ii) Measure the automatic pressure altitude at the output of the installed ATC transponder when interrogated on mode C at sufficient altitude levels up to the certified altitude of the aircraft. The following altitude levels will exercise all pulse positions up to 50,000 feet:
(F) 30,800'. The difference between the automatic reporting output and the altitude displayed on the aircraft altimeter shall not exceed 125 feet.
(2) Whenever an error is reported in the altitude reporting data, or when maintenance is performed on the system that could introduce a correlation error, the integration test shall be performed.
(3) Subject to subsection (2), when the maintenance performed consists of the installation of a line replaceable unit (LRU) and the installed LRU is a known airworthy part, the integration test need not be accomplished if an operational test is carried out prior to flight.