AMC 25J1093(b) Essential APU air intake system de-icing and anti-icing provisions

1.General In establishing compliance with the requirements of CS 25J1093(b), reference should be made to AMC 25.1093(b). All the reference made to “engine” may be transposed to “essential APU”. Engine test (especially CS-E 780) may refer to essential APU icing test done for the APU certification, if any. When the air intake is assessed separately, it should be shown that the effects of air intake icing would not invalidate the icing tests of CS-APU. Factors to be considered in such evaluation are: a. Distortion of the airflow and partial blockage of the air intake. b. The shedding into the APU of air intake ice of a size greater than the APU has been shown to ingest. c. The icing of any APU sensing devices, other subsidiary air intakes or equipment contained within the air intake. d. The time required to bring the protective system into full operation

2.Operating limitations The conditions defined in CS 25J1093(b)(2), in terms of time and temperature, should be considered as limitations necessary for the safe operation in freezing fog, and made available to the crew in the Aeroplane Flight Manual (refer to CS 25.1581). Nevertheless, the applicant may use an analysis to substantiate safe operation of the APU at temperatures below the demonstrated minimum temperature. No limitation would then be required in the Aeroplane Flight Manual. Any additional substantiation provided by the applicant to demonstrate the capability of an extended exposure beyond the conditions defined in CS 25J1093(b)(2), based on further testing and/or analysis, will be considered by the Agency.

[Amdt 25/1]

[Amdt 25/16]