wilyflier:
"We all know the difference Viscount/Brit and Dart/Proteus but both engines were reverse (air) flow".
In words of one syllable (or maybe two) - boll*cks.
The Proteus as fitted to the Britannia was indeed a reverse flow engine but the RR Dart was most certainly not.
For those of you who are unfamiliar with reverse flow turbo prop engines, here comes a simple explanation.
The only reason to have a reverse flow engine is to reduce the length of the engine and make it more compact (like the PT-6). So, the airflow enters the intake behind the prop and then goes through a 180 degree bend before entering the compressor. Then it goes through another 180 degrees before the combustion stage and then exiting through the turbine stage.
On the Britannia, the Proteus engines used to ice-up badly on the first U-bend and this caused the aircraft to be years and years late on entering service.
Even then, the problem was never satisfactorily solved. The civilian Brits had heating skins (B skins) fitted but their use caused a 10% loss in thrust. Even then, the engines were for ever shutting down and restarting (called "bumping") in icing conditions and this ensured that the crew never were allowed to go to sleep.
The RAF had a cowl heat system fitted but this resulted (so I'm told) in a 25% loss in thrust every time the system was used.
I will now move on to the RR Dart; I flew the Argosy for ten years and also the Viscount 802/806.
The Dart was a conventional engine in that there was no reversal of flow. It simply went: compression stage, combustion stage and then turbine stage. That is why the Dart was such a long and slim engine.
In fact, the engine was developed in a very simple fashion. When the Da 6 was not powerful enough, compression and turbine stages were added and so it was that the cowlings got longer right up to the Da 10.
I have never heard of four Darts failing at once through icing. I have personally had four inches of jagged ice on the engine intakes after an engine antice fault and not one of them even murmured.