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My IFR ATC-601 (only certain software versions), is displaying an UELM test and a DELM test but when the tests are run, why do the tests fail?

April 26, 2017atc-601 certain displaying IFR Software Test tests versions

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My IFR ATC-601 (only certain software versions), is displaying an UELM test and a DELM test but when the tests are run, why do the tests fail?

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It is a FAR Part 43 appendix F test requirement to test UF24 & DF24, where supported by the transponder. The transponder must be at least level 3 to support UF24 UELM (Up-link Extended Length Messages) and level 4 to support DF24 DELM (Down-link Extended Length Messages). The transponder must be connected to a suitable subsystem to either receive and/or supply data for multi-segment transfers. Most transponders do not support this service at this time. Failure of the test will not cause an Auto Test failure. If in doubt regarding the installed transponder capabilities, consult either the airframe manufacturer or the transponder manufacturer. Version 3.04 code uses the transponder capability report to determine if level 3 (UELM) is supported. If level 3 is not reported the IFR ATC-601 will not run the UELM test.