Definition 1 of 2
Definition
An error in the indication of an instrument caused by the way it is mounted in the aircraft, rather than by a fault in the instrument itself. It commonly affects pitot-static instruments (airspeed indicator, altimeter, vertical speed indicator) when the static port location produces pressure readings that differ slightly from true ambient static pressure, especially at certain airspeeds, attitudes, or configurations.
Plain English
A small reading error that comes from where and how an instrument is fitted in the aircraft, not from anything wrong with the instrument itself.
Context Anchor
Seen in aircraft instrument accuracy discussions, especially with airspeed indicators, altimeters, compasses, and systems that depend on outside air pressure.
Derivation
Installation comes from a word meaning to place or set something in position. Error comes from a Latin word meaning wandering or straying. Together, the term points to a reading that strays from the truth because of where the equipment was placed.
Why Pilots Care
Leads to inaccurate airspeed, altitude, or heading data that can affect navigation and safety decisions.
Grounding Statement
If an outside air-pressure opening is placed where the airflow is slightly disturbed, the instrument connected to it can read a little high or low even though it is not broken.
Intuition Check
Installation error does not necessarily mean someone installed the instrument incorrectly. It means the installed position in that particular airplane causes a small reading error.
Example Sentence 1
The airspeed correction chart in the POH shows the installation error at various flap settings and airspeeds.
Example Sentence 2
During the post-maintenance check the pilot noted a small installation error in the altimeter at field elevation.