Definition
A required flight crewmember on certain long-range or augmented flight crews, carried in addition to the minimum required pilots so that the pilot-in-command and second-in-command can take rest periods during the flight. A supplemental pilot must hold the certificates and ratings appropriate to relieve the pilot they are replacing at the controls.
Plain English
An extra qualified pilot carried on long flights so the main pilots can take turns resting while someone else flies the aircraft.
Context Anchor
Seen in crew assignment, air carrier operations, long flights, and discussions of crew rest or relief pilots.
Derivation
Supplemental comes from the Latin supplere, meaning 'to fill up' or 'to complete.' In this context, the pilot fills out the crew beyond the basic two-pilot minimum so the flight can legally and safely cover long durations.
Why Pilots Care
On long flights, regulations limit how many hours the pilot-in-command and second-in-command can be at the controls. Without a supplemental pilot, the flight cannot legally continue past those limits. Knowing the role matters for crew planning, duty time tracking, and understanding who is qualified to relieve whom.
Intuition Check
Do not read supplemental as meaning unofficial or optional in a loose sense. Here it means an additional qualified pilot added to the crew for a specific operational reason.
Example Sentence 1
On the twelve-hour transpacific flight, the supplemental pilot took the controls so the captain could go on rest break.
Example Sentence 2
Company policy assigns a supplemental pilot whenever the duty period exceeds the limits for a standard crew.