I’ve bolded a relevant part for the turbo alternate air box to avoid discussing over 22 pages how ice particles turn around corners and freeze the flap shut.
Serials w/o Perspective Avionics: Induction air enters the engine through a filter mounted on the left, forward side of the engine then flows into the induction duct assembly mounted center, forward on the engine. The induction duct assembly employs a flapper valve which, in the case of filter blockage, or induction ice, allows alternate air to enter the induction duct body via a flexible duct open to the RH cylinder area beneath the baffling of the engine. The alternate air valve is manually controlled from the cabin by pulling a control knob mounted on the left side of the center console.
From the induction duct body, induction air
flows to the throttle body after which the air is distributed to each cylinder via the intake manifold and separate intake tubes.
Serials 22-0002 w/ Perspective Avionics: Induction air enters the engine through a filter mounted on the right, forward side of the engine. In the case of filter blockage, or induction ice, a flapper valve assembly allows alternate air to enter the engine via a flexible duct open to the RH cylinder area beneath the baffling of the engine. The alternate air valve is manually controlled from the cabin by pulling a control knob mounted on the left side of the center console. From the filter, induction air flows to the throttle body after which the air is distributed to each cylinder via the intake manifold and separate intake tubes.
Serials 22T-0001 & subs: Induction air enters the engine compartment through two NACA ducts located in the lower LH and RH cowls. The induction air is ducted to the air boxes which house dual air filters. From the air filters, the air flows through the intercoolers to the throttle body, and is then distributed to each cylinder via the intake manifold and separate intake tubes. An overboost valve, located on the outlet tube of the LH intercooler, provides overboost protection if the manifold pressure becomes too high.
In the case of filter blockage, or induction ice, alternate air can enter the engine via the alternate air assembly. A tube from each air box leads to the alternate air assembly at the front of the engine. A blast tube connected to the heat exchanger provides heat to keep alternate air assembly flap from freezing. Under normal conditions, the alternate air assembly flap is held closed by a strip of magnets. When the air flow decreases, a vacuum is created that overcomes the pull of the magnets and allows the flap to open. After receiving a signal from a switch mounted to the alternate air assembly, the PFD will display “ALT AIR OPEN” in a yellow caution box. 28 VDC for the digital instrument operation is supplied through the 2-amp
ENGINE INSTR circuit breaker on the Essential Bus.
PA46 POH
Of course but I can recall several incidents where it wasn’t used leading to problems.
You must be referring to the springloaded alternate air doors in the (or at least some) turbo SR22. On most other airplanes, alternate air is controlled from the cockpit.
where in the POH have you find this? All I see in SR22 POH is
DA40-180 POH says to use alternate air in visible moisture, rain, snow.
DA42 POH (Diesel) too. And I can tell it is for good reason.
