If you’re not operating under a Minimum Equipment List that requires one, and the typical General Aviation pilot in the USA is not, then “No” is the answer to your posted question. There is no requirement for a VSI under FAR 91.205 hence no specific VSI inspection requirement is stated.
Note that in the USA prior to conducting flight under Instrument Flight ...
PPDM is Payload Power Distribution Module
SPMA is Sensor Processor Modem Assembly
RCM is Rabbitcore microprocessor Core Module
RVT Encoder is a Remote Video Terminal Encoder
As for what they do, that is at least For Official Use Only. You could always submit an FOIA request.
Hydrogen has to be in gaseous state to burn. The boiling point of hydrogen is ~20 kelvins, while oxygen boils at about 90 kelvins and freezes to solid at ~54 kelvins. It is therefore impossible to mix these two for combustion if hydrogen is in liquid state.
A non scientific answer to pumping liquid hydrogen directly to the combustion chamber is, that it will ...
In this youtube video showing landing gear maintenance operations on an ATR42, I'd say about 11 seconds for both extension and retraction.
A more precise timing could be gathered from an uninterrupted cockpit video, measuring from gear lever action action to "three green" on.