Civil Aviation Act: Part 1
Australian aircraft means:
(a) aircraft registered in Australia;
(it USED to say "on the Civil Aircraft Register" - which is VH only)
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CASA Aircraft Register Procedures Manual
2. Registration of Australian Civil Aircraft
2.3.2 Registration of Ultralight Aircraft
Ultralight aircraft are identified by a series of unique numbers constituted by the prefixes “10-“, “19-“, “24-“, “25-“, “28-“, “32-“, “55-“, followed by 4 digits. Theses prefixes are assigned according to the classification defined in the CAOs, 95.10, 95.55, 95.32, 101.28 and 101.55.
Whilst ultralights do not use the ICAO issued Australian prefix “VH” and they are not
registered in accordance with the provisions of the CASRs, CARs or this Manual, ultralight aircraft are considered to be Australian aircraft.
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Can you use it (RA-Aus machine) for AFR as the question relates?
Is it an aircraft? YES.
The RPL is about skills demonstration, competency based they call it. You can equally demonstrate those skills in a VH or RA-Aus aircraft. Your level of competency will not change.