14 CFR 23.1105 - Induction system screens.
If induction system screens are used -
(a) Each screen must be upstream of the carburetor or fuel injection system.
(b) No screen may be in any part of the induction system that is the only passage through which air can reach the engine, unless -
(1) The available preheat is at least 100 °F.; and
(2) The screen can be deiced by heated air;
(c) No screen may be deiced by alcohol alone; and
(d) It must be impossible for fuel to strike any screen.