alternate air in visible moisture

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bd32322
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alternate air in visible moisture

Post by bd32322 »

Anyone read or know if alternate air should be used in visible moisture? The POH indicates use of alternate air only if primary induction air is blocked e.g. in icing. But my CFI quoting a well known book/source says to use alternate air in visible moisture - which makes no sense to me.

Any info?

Thanks
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Re: alternate air in visible moisture

Post by jb642DA »

"The POH indicates......"
You didn't say which plane you are flying???!!!


Check the plane's AFM - Systems description section and normal/emergency procedures sections say a fair amount about ALTERNATE AIR use. All the Diamond Aircraft Flight Manuals are available online. They are also "required equipment" in each aircraft!.

From DA62 AFM - some statements regarding Alternate Air for engine -

When safe climb is established:
ALTERNATE AIR.....................OPEN; in rain, snow or visible
moisture
(YES, your CFI is right)


4A.6.18 FLIGHT IN RAIN
1. ALTERNATE AIR...................OPEN

CAUTION
During operation on ground ALTERNATE AIR must be
CLOSED.
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Re: alternate air in visible moisture

Post by ememic99 »

Since the question is posted in DA42 forum, I would assume OP flies DA42 :)

DA42 POH specifies opening alternate air in icing conditions which means low temperatures (I would say slightly above 0C and lower) and visible moist. I encountered airframe icing anywhere from +2 to -25 degrees C. I don't see reason why to open alternate air in case of rain at high temperature.
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Re: alternate air in visible moisture

Post by bd32322 »

Yeah this is for a DA42 - thanks for the replies ..
Yeah I was unable to find anything in service manuals or POH that would indicate opening alt air in visible moisture much above freezing
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Re: alternate air in visible moisture

Post by jb642DA »

ememic99 wrote: Fri Jul 12, 2019 4:50 pm Since the question is posted in DA42 forum, I would assume OP flies DA42 :)

DA42 POH specifies opening alternate air in icing conditions which means low temperatures (I would say slightly above 0C and lower) and visible moist. I encountered airframe icing anywhere from +2 to -25 degrees C. I don't see reason why to open alternate air in case of rain at high temperature.
Sorry Emir - I should have asked TDi vs Austro.

I didn't find the "visible moisture" reference in the AFM for the 42TDi - I only found the "visible moisture" statement in the 42/62 Austro engine AFMs.
Last edited by jb642DA on Sat Jul 13, 2019 12:45 pm, edited 1 time in total.
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Re: alternate air in visible moisture

Post by ememic99 »

jb642DA wrote: Sat Jul 13, 2019 12:37 pm
ememic99 wrote: Fri Jul 12, 2019 4:50 pm Since the question is posted in DA42 forum, I would assume OP flies DA42 :)

DA42 POH specifies opening alternate air in icing conditions which means low temperatures (I would say slightly above 0C and lower) and visible moist. I encountered airframe icing anywhere from +2 to -25 degrees C. I don't see reason why to open alternate air in case of rain at high temperature.
Sorry Emir - I should have asked TDi vs Austro.
:D Can you explain the difference since you have experience with both engine types? Why would be Austro be more susceptible to moist above freezing level than CD?
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Re: alternate air in visible moisture

Post by jb642DA »

I never looked into the "why" part of the differences between the TDi engine (Theilert 2.0 in our case) and the Austro. I just try to operate it per the "Normal procedures" section.

Would be interesting to know the "why" though!
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Re: alternate air in visible moisture

Post by jb642DA »

Emir - Is your 42 a TDi/CD or Austro engine plane?
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Re: alternate air in visible moisture

Post by ememic99 »

CD-155 Crosby conversion.
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Re: alternate air in visible moisture

Post by jb642DA »

Nice!
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