GA Aircraft ditching - Irish Sea - 16th Dec
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Quote: The only thing that can cause a prop overspeed is a failure of both governors within the CSU. Not quite true, lose of pressure (Nitrogen/air) in the prop dome will cause and over speed as well
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Big Blue Scuba Divers in Port Vila,Vanuatu have recently sunk a twin engine Pipe Comanche Twin engine aircraft for recreational divers to enjoy while also creating an artificial reef for marine life to enjoy!
YouTube - Big Blue Vanuatu
YouTube - Big Blue Vanuatu
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Six months is a long while between ditching and recovery plus there is likely to be quite a bit of recovery damage, it will be very interesting to see what is found wrong with the aircraft.
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My understanding is one must slow the aircraft down to the point where the RPM on the fine stops is within the target range in governor failure modes such as described. There is no indication in the narrative this was attempted.
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If there is enough airflow (speed) to overspeed a prop which is against its fine pitch stop, with the throttle shut, then surely shutting down that engine is not going to make much of an additional improvement.
As you say, one needs to slow down a bit.
As you say, one needs to slow down a bit.
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Prop runaway: options
Easy to judge from the couch and not being in danger:
vyse and zero thrust on the engine will keep the prop well below max. RPM when the propeller is at it's most fine position with no pressure against oil pressure.
Some reduced positive thrust will be possible at blue line with max. RPM.
Shutting down the engine doesn't help at all, because the propeller continues windmilling. You can't feather a runaway prop unless cutting oil pressure and having left some opposing pressure (nitrogen or spring). Windmilling engine creates its own oil pressure.
Even a very lightly loaded TwinCo will hardly hold 3000 ft with a windmilling prop.
These thoughts are no judgements for the decissions on this flight, but should help others in a similar case.
Regards and safe flying,
Andi
vyse and zero thrust on the engine will keep the prop well below max. RPM when the propeller is at it's most fine position with no pressure against oil pressure.
Some reduced positive thrust will be possible at blue line with max. RPM.
Shutting down the engine doesn't help at all, because the propeller continues windmilling. You can't feather a runaway prop unless cutting oil pressure and having left some opposing pressure (nitrogen or spring). Windmilling engine creates its own oil pressure.
Even a very lightly loaded TwinCo will hardly hold 3000 ft with a windmilling prop.
These thoughts are no judgements for the decissions on this flight, but should help others in a similar case.
Regards and safe flying,
Andi
