The bucket system
Every seat on a flight is sold through booking classes — single letters, each tied to a fare with its own price and conditions. Traditionally, F is full-fare first, J full-fare business, W or premium-economy letters sit in the middle, and Y is full-fare economy, with the rest of the alphabet (B, H, K, L, M, N, Q, S, V, Z and friends) cascading down through progressively cheaper, more restricted economy fares.
Every seat on a flight is sold through booking classes — single letters, each tied to a fare with its own price and conditions. Traditionally, F is full-fare first, J full-fare business, W or premium-economy letters sit in the middle, and Y is full-fare economy, with the rest of the alphabet (B, H, K, L, M, N, Q, S, V, Z and friends) cascading down through progressively cheaper, more restricted economy fares.
Crucially, the letters describe the fare, not the seat. A passenger in 24A on a Y ticket and a passenger in 24B on a Q ticket get the same physical seat and meal — but the Y passenger paid perhaps three times more for a ticket that's refundable, changeable, and earns full miles.
Airlines vary the exact letters, but the logic is universal: every carrier publishes a ladder of fares per cabin, and availability opens and closes bucket by bucket.
Revenue management: the pricing engine
Behind the buckets sits revenue management — the discipline, and the software, that decides how many seats to release in each bucket on each departure. The goal is to fill the plane at the highest average fare: sell too cheap too early and the plane fills with low-yield passengers; hold out too long and seats fly empty.
Behind the buckets sits revenue management — the discipline, and the software, that decides how many seats to release in each bucket on each departure. The goal is to fill the plane at the highest average fare: sell too cheap too early and the plane fills with low-yield passengers; hold out too long and seats fly empty.
The models ingest booking pace, historical demand, seasonality, events and competitor pricing, and re-optimise constantly. That's why the fare you saw on Tuesday is gone by Friday — not because "prices went up" in the abstract, but because the cheapest buckets closed as the flight's bookings tracked ahead of forecast.
It also explains the classic patterns: fares rising in the last few weeks before departure (cheap buckets long gone), and eye-watering prices on the last seats (only full-fare buckets remain, priced for business travellers whose companies pay).
What your bucket buys you
The fare rules attached to your bucket govern almost everything after purchase. Refundability and change fees: deep-discount buckets are typically use-it-or-lose-it, while full-fare buckets change and refund freely. Baggage and seat selection: the cheapest "light" or "basic" buckets strip both.
The fare rules attached to your bucket govern almost everything after purchase. Refundability and change fees: deep-discount buckets are typically use-it-or-lose-it, while full-fare buckets change and refund freely. Baggage and seat selection: the cheapest "light" or "basic" buckets strip both.
Mileage earning varies by bucket too — many airlines award a percentage of flown miles based on booking class, so the cheapest fares may earn 25% or nothing at all. And when things go wrong, full-fare buckets get rebooked first and most flexibly; the fine print of your bucket is the fine print of your disruption rights.
Buckets and upgrades
Upgrade instruments — miles, vouchers, or airport standby lists — almost always work bucket-first. Airlines typically only upgrade from eligible booking classes, and the eligible classes are rarely the cheapest ones. This is the catch behind "upgrade with miles from £X" marketing: the cheap fare you bought may be ineligible, while a mid-price bucket two rungs up qualifies.
Upgrade instruments — miles, vouchers, or airport standby lists — almost always work bucket-first. Airlines typically only upgrade from eligible booking classes, and the eligible classes are rarely the cheapest ones. This is the catch behind "upgrade with miles from £X" marketing: the cheap fare you bought may be ineligible, while a mid-price bucket two rungs up qualifies.
Operational upgrades — when economy is oversold and passengers are moved forward for free — also follow a pecking order: status first, then fare bucket, then check-in time. It's one more way the humble letter on your booking follows you to the gate.