Glossary
Definition: Circadian rhythm is the body’s natural 24-hour internal clock that regulates sleep-wake cycles, hormone release, and other physiological processes. Long-haul air travel disrupts this rhythm, causing jet lag.
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Term at a glance
| Term | Circadian Rhythm |
|---|---|
| One-liner | Circadian rhythm is the body’s natural 24-hour internal clock that regulates sleep-wake cycles, hormone release, and other physiological processes. Long-haul air travel disrupts… |
| Where it matters | Premium-cabin booking decisions, fare-rules interpretation, airline-product comparison. |
| Related concepts | Jet Lag · Lie-Flat Seat · Red-Eye Flight · Boeing 787 Dreamliner · Turn-Down Service |
| Last verified | 2026-05-07 |
Your circadian rhythm is controlled by a cluster of cells in the brain’s hypothalamus that respond primarily to light cues. When you travel across time zones, these cells need time to adjust to the new light-dark cycle, creating the misalignment that causes jet lag symptoms.
Airlines and travellers employ various strategies to manage circadian disruption. Many business class passengers adjust their sleep schedule before departure, use melatonin to encourage sleep at the destination’s nighttime, and maximise light exposure at strategic times after arrival.
In premium cabins, airlines support circadian adjustment through meal timing (serving dinner when it’s evening at the destination), cabin lighting that simulates day/night cycles, and lie-flat seats that allow sleeping at the appropriate time. Modern aircraft like the 787 and A350 feature LED lighting systems that gradually shift through a spectrum of colours to support natural sleep-wake transitions.
In booking practice
At a Glance
| Term | Quick definition | Reference |
|---|---|---|
| Chauffeur Drive | Chauffeur drive is a complimentary ground transfer service offered by select airlines to first and business… | Read |
| Club Suite (British Airways) | British Airways' refreshed business class product, replacing the previous Club World cabin. Features 1-2-1… | Read |
| Change Fee | A fee charged by airlines to modify a booking after purchase — typically applied to non-refundable fares.… | Read |
| Codeshare | A codeshare is a commercial arrangement where two or more airlines sell seats on the same flight under… | Read |
| Carrier Surcharge (YQ) | A cash-fee component charged by certain carriers on award redemptions, on top of government taxes and the… | Read |
| Companion Ticket | A companion ticket (or companion certificate) is a benefit that allows an elite frequent flyer or credit card… | Read |
Related Terms
Chauffeur drive is a complimentary ground transfer service offered by select airlines to first and business class passengers, providing a luxury car and driver to take you to or from the airport.
British Airways' refreshed business class product, replacing the previous Club World cabin. Features 1-2-1 reverse herringbone configuration with full sliding doors, direct aisle access from every seat, and a 23-inch IFE screen.
A fee charged by airlines to modify a booking after purchase — typically applied to non-refundable fares. Most major US airlines eliminated change fees on most international tickets in 2020-2021, though some restrictions returned in 2024-2025 on the deepest discount fare buckets.
A codeshare is a commercial arrangement where two or more airlines sell seats on the same flight under different flight numbers, allowing each airline to market the flight as its own.
A cash-fee component charged by certain carriers on award redemptions, on top of government taxes and the mileage cost. Carrier surcharges (often coded YQ on tickets) reflect fuel-cost recovery in the historic IATA fare construction; the actual fee rarely correlates with current fuel prices in 2026.
A companion ticket (or companion certificate) is a benefit that allows an elite frequent flyer or credit card holder to book a second ticket for free or at a deep discount when purchasing a full-fare ticket.
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