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Transponder Certification 


Transponder Modes A/C/S


Certification Per CFR 91.413

We accomplish your Transponder & Altitude encoder tests using the latest "state of the art" test equipment from Aeroflex, the IFR 6000. In addition we are certified for installation, repair, and calibration of all models of transponders and altitude encoders. All work is accomplished by an FAA certified AP-IA mechanic (not all repair stations use certified mechanics).

Inspections Required for VFR and IFR operations:

The aircraft transponder must be certified every 24 months in accordance with the requirements of CFR 91.413. These tests consists of:

  • Transponder tested for proper operation per CFR Part 43, Appendix 'F'.

  • Automatic Altitude encoder Data Correspondence test per CFR 91.217 (required for new installations or when altimeter or altitude encoder is repaired/replaced).

More info can be found on our FAQ page.


We use the Aeroflex IFR 6000 to test all modes of transponder operation including Modes: A, C, S, Altitude reporting, ADS-B in/out, UAT and DME.

Altitude data is  supplied to the transponder from the altitude encoder or digitizer which then transmits that information to ATC, this altitude is displayed on the IFR 6000 during testing. 

The accuracy of the IFR 6000 enables us to easily meet or exceed all manufacturer specifications.


CFR ref's:

§ 91.215 ATC transponder and altitude reporting equipment and use.

(a) All airspace: U.S.-registered civil aircraft. For operations not conducted under part 121 or 135 of this chapter, ATC transponder equipment installed must meet the performance and environmental requirements of any class of TSO-C74b (Mode A) or any class of TSO-C74c (Mode A with altitude reporting capability) as appropriate, or the appropriate class of TSO-C112 (Mode S).

(b) All airspace. Unless otherwise authorized or directed by ATC, no person may operate an aircraft in the airspace described in paragraphs (b)(1) through (b)(5) of this section, unless that aircraft is equipped with an operable coded radar beacon transponder having either Mode 3/A 4096 code capability, replying to Mode 3/A interrogations with the code specified by ATC, or a Mode S capability, replying to Mode 3/A interrogations with the code specified by ATC and intermode and Mode S interrogations in accordance with the applicable provisions specified in TSO C–112, and that aircraft is equipped with automatic pressure altitude reporting equipment having a Mode C capability that automatically replies to Mode C interrogations by transmitting pressure altitude information in 100-foot increments.

Link to the complete FAR 91.215

§ 91.217   Data correspondence between automatically reported pressure altitude data and the pilot's altitude reference.

(a) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder—

(1) When deactivation of that equipment is directed by ATC;

(2) Unless, as installed, that equipment was tested and calibrated to transmit altitude data corresponding within 125 feet (on a 95 percent probability basis) of the indicated or calibrated datum of the altimeter normally used to maintain flight altitude, with that altimeter referenced to 29.92 inches of mercury for altitudes from sea level to the maximum operating altitude of the aircraft; or

(3) Unless the altimeters and digitizers in that equipment meet the standards of TSO-C10b and TSO-C88, respectively.

(b) No person may operate any automatic pressure altitude reporting equipment associated with a radar beacon transponder or with ADS–B Out equipment unless the pressure altitude reported for ADS–B Out and Mode C/S is derived from the same source for aircraft equipped with both a transponder and ADS–B Out.

§ 91.413   ATC transponder tests and inspections.

(a) No persons may use an ATC transponder that is specified in 91.215(a), 121.345(c), or §135.143(c) of this chapter unless, within the preceding 24 calendar months, the ATC transponder has been tested and inspected and found to comply with appendix F of part 43 of this chapter; and

(b) Following any installation or maintenance on an ATC transponder where data correspondence error could be introduced, the integrated system has been tested, inspected, and found to comply with paragraph (c), appendix E, of part 43 of this chapter.

(c) The tests and inspections specified in this section must be conducted by—

(1) A certificated repair station properly equipped to perform those functions and holding—

(i) A radio rating, Class III;

(ii) A limited radio rating appropriate to the make and model transponder to be tested;

(iii) A limited rating appropriate to the test to be performed;

(2) A holder of a continuous airworthiness maintenance program as provided in part 121 or §135.411(a)(2) of this chapter; or

(3) The manufacturer of the aircraft on which the transponder to be tested is installed, if the transponder was installed by that manufacturer.

Please contact us for more info.