No to alterante air, for me
Kevin Horton said:
I am aware of two RVs that had off-field landings after the air filter was clogged with snow. The anemic Van's carb heat system did not provide enough heat to melt the snow. I am also aware of an aircraft (not an RV) that was downed by hitting something in flight that clogged the air filter. I believe every RV should have an air filter bypass.
I agree with Kevin but don't agree with his conclusion. I don't fly in snow so my opinion is you don't need it. I only know of one blockage that occurred, regardless it is YOUR OPTION.
Keep in mind there is "Impact Blockage" like snow and Carb Ice, two different things.
My rational, any weather condition that could block the filter, like snow, can be counteracted by applying CARB HEAT. The carb heat door blocks the outside air and eliminates any chance of snow blocking or "Impacting" the filter.
It's obvious when you are in snow or any precipitation, so it's not a burden to remember to use carb heat when in rain, snow, sleet or freezing fog/drizzle/rain. However if you are in any of these conditions, especially for a VFR pilot, you may be in deep dodo already, regardless of bypass air or not.
I am leaving it off for now, but I did order it. I can always add it later. VFR flying no, not needed. IFR flying? Yea worthy of consideration, but the above carb heat anti-blockage procedure still applies.
The old magnetic bypass set-up was worthless, however the new version bypass, the cable operated one looks better, but keep in mind any hardware that can get loose could go directly into the engine. The by pass is right there under the throat of the carb or FI body and with no filter. I don't have my installation instructions handy but you need to assure the hardware you install on the FAB bottom for the bypass can not get loose or sucked into the engine. I leaving it off because of weight, worry of ingestion of parts and I don't fly in snow, if I did I have a fall back, carb heat door blocking the snow from blocking the filter.
There was one case of a bird getting sucked into the scoop of a RV, true story and its documented in a back issue of the RVator. Things can happen but the chance is so small it's not worth the effort to install. According to Van's that is their conclusion if you read the service bulletin, it is dependant on the weather you plan on flying in.