Why counting flights and seats from SSIM is harder than it looks

“How many flights a week, and how many seats?” is the first question anyone asks of a schedule, and the one most often answered wrongly. The figures look simple. They aren’t, because an SSIM file never states them: each flight leg record describes a pattern — a period, some weekdays, an aircraft, a cabin — and the numbers only exist once those patterns are turned into actual departures in an actual week.

Every step of that turns out to have a trap.

The traps

• Which week? A schedule covers a season. Pick the wrong week — one with a holiday, a schedule change or the tail of the season — and the “typical week” isn’t typical.
• Whose clock? Days of operation are stated on a clock. Count them on another and a late-evening departure moves to the next day, shifting frequencies between days and, at the edges, between weeks.
• Code shares counted twice. One aircraft can carry several flight numbers. Count every flight number as a departure and a busy route can appear a third larger than it is. Wet leases and shared designations blur the line further.
• Seats that aren’t stated. Many records state the cabin configuration; some don’t, and some state a placeholder. Fill the gaps carelessly and the seat count drifts.
• Surface and non-passenger legs. Trucks, trains and freighters can sit in the same file as passenger flights. Leave them in and capacity is overstated.
• Multi-leg flights. A flight that stops on the way is several legs and several segments. Count the wrong one and a route gains — or loses — seats it doesn’t have.

None of these produces an error. Each produces a plausible number.

Why it matters

Frequencies and seats are the basis of market share, competitive analysis, capacity planning and airport forecasts. A figure that is quietly inflated by double-counted code shares, or shifted by a day boundary, leads to decisions made on capacity that doesn’t exist — and to comparisons between airlines that aren’t like for like.

The question to ask of any capacity figure is not “is this roughly right?” but “can I trace it back to the records it came from?”

Where SSIM Toolkit fits

SSIM Toolkit counts departures, seats and seat-kilometres for the period, airlines and clock you choose — operated flights only unless you ask otherwise, estimated seats marked as estimated — and every figure traces back to its records. Markets, competition and capacity pages build on the same counts, so they always agree with each other.

See your own schedule counted properly. SSIM Toolkit comes with a 30-day free trial.

FAQ

Why do two tools give different frequencies for the same schedule? Usually because they made different choices about the week, the clock, code shares or non-passenger legs. Each choice is defensible; mixing them is not.

Are seats in an SSIM file always exact? No. When a record doesn’t state its configuration, seats have to be estimated from the aircraft type, and that estimate should be labelled as one.

Do code shares count as frequencies? For the operating airline’s capacity, no — the same departure would be counted once per flight number. For a marketing view they may be wanted, but kept apart.