Definition
A screen or filtering element installed at the air intake of a pneumatic system, typically the engine-driven vacuum or pressure pump system, that removes dust, dirt, and contaminants from the air before it enters the system and reaches the gyroscopic instruments.
Plain English
A filter that cleans the air going into the system that powers some of the cockpit instruments, so dirt does not get in and damage them.
Context Anchor
Seen in diagrams and maintenance discussions of instrument pressure or vacuum systems, such as the system shown with cockpit instruments and an air source.
Derivation
Inlet means the place where something enters. Filter comes from medieval Latin filtrum, a piece of felt used to strain liquids. Together: the strainer at the entry point.
Why Pilots Care
Ensures accurate pressure measurements for airspeed, altitude, and vertical speed by keeping the lines clear of contaminants that could cause instrument errors.
Intuition Check
Do not confuse an inlet filter with the engine air filter. Here, it filters air entering an instrument system, not air entering the engine.
Example Sentence 1
A clogged inlet filter can reduce vacuum pressure and cause the attitude indicator to become sluggish.
Example Sentence 2
A clogged inlet filter in the static system can lead to incorrect altitude indications.