I seem to remember that the BO105 had an air pressure switch to indicate a fan drive failure. A simple system to give the pilot cockpit information about the fans condition.
The reason being that originally there was no ram air for the coolers (engine and gearbox).
The aircraft was modified to provide a ram air system.
The 139 MRGB has no ram air system (the engine oil systems being fuel cooled). The 139 is not alone in this respect. It seems a little extreme to loose an aircraft for the want of air when it is passing by at 100+ knots.
Last edited by ericferret; 7th May 2017 at 11:07.