Jepps Terminal 1.6.1
Except when complying with the requirements for a visual approach, when conforming to a published DME or GPS arrival procedure, or when identified and assigned an altitude by ATC, an aircraft approaching an aerodrome must not descend below the LSALT or the MSA for the route segment being flown until it has arrived over the IAF or Facicility.
So unless DME/GPS arrival, then fly over the aid or IAF before starting the APP.