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I've recently come across the same question in both the IREX book and the BT online exams, but each gave a different answer.
"You are establishing a lowest safe altitude tolerance area prior to take-off for a flight from Alpha to Bravo. The route does not appear on the ERC. Alpha has an NDB, but Bravo has no navigation aid. If the distance from Alpha to Bravo is 60nm, the tolerance area must include a semicircle centred on Bravo.
The radius of this semicircle would be closest to - "
The book says its 15.3nm (due to the 5nm buffer) but the online exam says 10.3nm (since the question did not specifically ask for the 5nm buffer).
Any thoughts on whether the 5nm buffer should be added if the question did not specifically ask for it?
You can be sure that in a CASA exam, the question will make it clear whether or not to include the 5nm buffer. Remember that if the question asks for the 'tolerance area', it would always include the 5nm buffer.