I know someone who ditched a twin Comanche in the Irish Sea after suspected alternate air door icing. (You always suspect running out of fuel when a twin has a double engine failure, but the AAIB still found fuel in the aircraft after it had been on the bottom of the sea for 3 months)
You have to open alternate air before you enter icing conditions.
You can’t open the alternate air door as there is no manual control of this door in the SR22 Turbo. It is automatic. On the COPA forum they suggest a leakage in the air induction system.
This is what they wrote:
I know you think the alternate air door is the culprit but this really does not add up. Why?
1) The alternate air door is on the bottom of the engine out of the slip stream of air so ice typically cannot form there.
2) The alt. air door is bathed in warm air from the engine under the cowl.
3) Loss of MP pressure in this setting is almost always a leak in the induction air system. It will resolve with a descent as the pressure differential between ambient pressure and the compressed air in the turbo decreases.
Someone else suggested a “blown up upper deck reference line” which has to do then with the Turbo.
I thought about an induction leak / turbo problem first when we talked. However, why would the alternate air door open then? You had the cockpit indication.
With respect to the writer, Aeroplus, I completely don’t understand his comments.
The alternate air door is on the bottom of the engine out of the slip stream of air so ice typically cannot form there.
The ice would form inside the air duct!
The alt. air door is bathed in warm air from the engine under the cowl.
Loss of MP pressure in this setting is almost always a leak in the induction air system. It will resolve with a descent as the pressure differential between ambient pressure and the compressed air in the turbo decreases.
An induction leak would not rob the engine of air; in fact it would be quite a useful thing in the circumstances
Peter wrote:
The air temp under the engine is the OAT (say -25C) minus the temperature rise through passing through the cylinder fins. I don’t know this delta-T (as I wrote earlier, it needs a flight test with a suitably instrument aircraft, and nobody is going to own up to having done such a flight because it can’t be done legally, and I bet nobody in the industry has ever done it anyway because nobody is going to question decades-old assumptions) but if it is say 20C then you get -5C under the engine, which is just perfect for structural icing.
I have a carb temperature gauge and even at FL200 at -35°C, the air temperature is positive
An induction leak would not rob the engine of air; in fact it would be quite a useful thing in the circumstances
He’s got a turbocharger, a leak between turbo and engine would take MP away.
“An induction leak would not rob the engine of air; in fact it would be quite a useful thing in the circumstances”
Not in a turbo
Not in a turbo
Not sure if I understand your drift right (maybe you can explain more) but even with a turbo, the engine would be making power when the turbo is not spinning. In Aeroplus’ case, AIUI, he had a total loss of power. That is consistent only with a total loss of airflow into the engine.
I have a carb temperature gauge and even at FL200 at -35°C, the air temperature is positive
That is however the carb body. Not the temp of the air flowing through it. The air temp and thus the potential for icing up objects which protrude into it, depends on how fast the air is flowing. If the -35C air is flowing fast enough, the carb body could be at +100C and you would still be below zero in the relevant bits of the airflow.
He’s got a turbocharger, a leak between turbo and engine would take MP away.
Would it take it away almost totally? At FL230 you should get maybe 30% of max rated power.
He did not say he lost all engine power, he mentioned MP 11".
Also an iced up induction would not suddenly reduce the power from full to none, it would be a gradual loss as the induction gradually turns into an orifice.
If you have such a strong turbo aircraft and operate it at high altitudes, an induction loss or turbo failure feels like an engine failure.
He did not say he lost all engine power, he mentioned MP 11".
That sounds like a windmilling engine sucking against a blockage. You won’t get zero MP (a vacuum).
Also an iced up induction would not suddenly reduce the power from full to none
Want a bet?
What actually happens with these things is that one gets caught out, because one is not watching the IAS 100% of the time.
