Wheeler,
That is correct,
if it is on the MR. If it is not on the MR then perhaps you need to take the issue up with your LAME and ascertain if you can conduct a 50 hourly check +/- 10%. If the answer is yes (under your operating system) then have him amend the MR.
Pitch Pull,
If a MR specifies the 50 hourly is to be carried out at 50 hours; and you opt to do it at 40 hours; then you will have to conduct another 50 hourly at 90 hours, or turn the aircraft in for a fresh 100 hourly with 10 hours left on the MR. Most aviation managers would prefer to run as close as possible to the 100 hourly to reduce operating costs.
GA Driver,
Section 20AA of the Act states
(3) An owner, operator, hirer (not being the Crown) or pilot of an Australian aircraft must not commence a flight or permit a flight to commence if … (b) a maintenance release under the regulations that covers the duration of the flight is not in force in respect of the aircraft and the regulations do not authorise the flight without the release. Penalty: Imprisonment for 2 years.
CAR 41 places the onus on the certificate of registration holder to undertake maintenance when required. Penalty 50 penalty units.
If your MR looks like expiring towards the end of a trip you need to roster another aircraft or arrange to ferry back and have it renewed. If it runs out mid-flight seek legal aid!
