KeepItStraight said:
Induction icing is unlikely to cause a power lose due to the location of the intake plus the Comanche is fitted with automatically opening alternate air doors which can be also opened manually.
You may well be right, and this could well have no bearing at all on the accident in question.
However, it is certainly interesting to note that the alternate air door design in the the PA30 is poor and has been responsible for engine failures (and, I understand, double engine failures) through air inlet blockage in the past. From an air accident report:
The original design of the alternate air door on the normally aspirated PA30's and PA39's puts the door downstream of the air filter and in an area of high vibration. A failure of the door hinge or shaft will lead to an immediate engine failure. A modification exists to move this door to a lower vibration area on the lid of the air filter. If not modified, this door should be inspected thoroughly and frequently (we have had an Australian fatality due to this).
And from a separate Twin Comanche incident arising from alternate air door failure:
I was flying my PA-30 over water together with my friend Michael in his PA-39. My position was some 200 ft behind and to his right side (we flew many thousands of miles that way, with the leading aircraft calling for both as "Comanche Formation"). All of a sudden it looked like he applied brakes: His aircraft slowed down and in a second I was at his level. I throttled back and we exchanged ideas about what went wrong, as all gauges were normal. All of a sudden he started to accelerate and soon operation was normal. This repeated itself several times to our amazement. However, he was able to make it safely to destination. After landing we started to look for a possible cause and it did not take long to find that one of these doors got loose and partially blocked the air passage. When it moved back and forth the size of the free passage was changed. Fortunately, there was never a full block.
Thus the lack of prop RPM stability through a wildly fluctuating manifold pressure could be explained! Of course, as I said, this could well have no bearing at all on the accident in question.