G'Day 'ACMS',
I think you may find that the 727 concerned descended into Pingelly NDB,
ident at the time, 'PGL', instead of the locator at Parkerville, ident 'PRL'.....
Yep - he 'misappeared'.....low enough to be out of VHF comms - but popped back up again and continued to PH.
Pingelly NDB ident changed to 'PIY' soon after....
Whew!!