R22 & R44 Pitot-Static Drain Plugs

The R22 & R44 systems section of the POH describes the pitot-static system and talks about plastic drain plugs, accessible through an inspection panel on the belly of the fuselage. Because of their location, most pilots don’t get to see these plugs, and it is a maintenance function to drain the lines if needed.

See below image from the R44 pitot-static system, with the inspection panel removed and the the drain plugs installed:

And here we see the same R44 pitot-static system, with one of the drain plugs removed:

As the POH describes, the purpose of the drain plugs is to remove water that has collected in the system, especially if the airspeed or altimeter reading seems erratic. I have personally witnessed this a few times and it was caused by water in the system after a heavy storm.