Definition
The loss or malfunction of an aircraft system or instrument that prevents it from providing accurate information or normal operation. In the context of analog flight instruments, a system failure is the breakdown of one of the underlying sources that drive the instruments — typically the pitot-static system, the vacuum (or pressure) system, or the electrical system — causing one or more cockpit indications to become unreliable, frozen, or absent.
Plain English
Something that powers or feeds an instrument has stopped working, so the instrument is no longer giving you correct information. The dial may still be sitting there looking normal, but you can't trust what it's showing.
Context Anchor
Seen in instrument flying when discussing failures of the systems that supply or support cockpit instruments.
Why Pilots Care
A system failure removes reliable instrument data and requires immediate use of backup instruments or partial-panel techniques to keep the airplane upright.
Intuition Check
Do not assume system failure means the whole airplane has failed. In this context, it may mean one aircraft system or instrument-supporting system is no longer reliable.
Example Sentence 1
When the airspeed indicator and altimeter both began behaving oddly, the pilot suspected a pitot-static system failure rather than a single instrument problem.
Example Sentence 2
During the flight review the instructor simulated a vacuum system failure to practice instrument cross-check without the attitude indicator.