Definition
Equipment, instruments, or items installed on an aircraft that are not required for the safe operation of the specific flight being conducted under the applicable regulations, aircraft type certificate, and operating conditions. Items in this category may be inoperative for a flight provided the aircraft is operated in accordance with an approved Minimum Equipment List (MEL) or, where no MEL exists, the inoperative equipment provisions of 14 CFR 91.213(d).
Plain English
Things on the aircraft that don't have to be working for this particular flight to be legal and safe. They can be broken or missing as long as the rules for flying with them inoperative are followed.
Context Anchor
Seen when deciding whether an airplane may be flown with an item that is not working.
Derivation
From Latin essentia (the necessary nature of something) with the prefix non- (not). 'Nonessential' literally means 'not necessary' — here, not necessary for this specific flight under the rules that apply to it.
Why Pilots Care
Determines whether a flight can legally continue with certain equipment inoperative, directly affecting go/no-go decisions and maintenance scheduling.
Intuition Check
Do not read “nonessential” as “ignore it.” It means “not required for this specific flight,” and the item still has to be dealt with correctly before flying.
Example Sentence 1
Because the cabin reading light was classified as nonessential equipment, the pilot deferred the repair under the MEL and departed on schedule.
Example Sentence 2
Before accepting the aircraft, the crew verified that all nonessential equipment failures were properly documented and did not affect required systems.