Airline unit revenue and unit cost: RASK and CASK
Yield, fares, RASK, CASK and CASK ex-fuel.
By Surojit Chakraverti, founder of L3VLUP and an investor running a long-short healthcare and technology equities strategy.
On this subject: airline unit revenue and unit cost: rask and cask.Updated 22 October 2026
What it does
An airline is judged per seat kilometre. Revenue is passengers times the average fare, which is the yield (revenue per RPK) times the distance flown, plus ancillary revenue per passenger and cargo carried in the hold; over ASK it is RASK. Costs are built from what causes them: crew and maintenance by the block hour, airport charges by the departure and the passenger, navigation by the kilometre, overheads by the seat kilometre; over ASK they are CASK. CASK ex-fuel strips out the one cost the airline does not set, which makes it the measure of how well it is run. RASK less CASK, times ASK, is operating profit.
Where it lives
The same schedule in each model that carries it, with the rows to open. Open a model in the browser, go to the sheet, and click the lines.
- Assumptions, rows 37–42: Narrowbody yield, FY0A, Widebody yield, FY0A, Yield change, base case, Ancillary revenue per passenger, FY0A…
- Assumptions, rows 52–62: Unit cost inflation, annual, Narrowbody: crew cost per block hour, FY0A, Widebody: crew cost per block hour, FY0A, Narrowbody: maintenance per block hour, FY0A…
- Revenue, rows 15–20: Narrowbody: yield, base case, Narrowbody: yield, selected scenario, Narrowbody: average fare, Widebody: yield, base case…
- Revenue, rows 23–30: Narrowbody: passenger revenue, Widebody: passenger revenue, Passenger revenue, Ancillary revenue per passenger…
- Revenue, rows 33–35: Passenger yield, both fleets, Passenger revenue per ASK (PRASK), Revenue per ASK (RASK)
- Costs, rows 15–23: Unit cost index, Crew, Maintenance, Airport charges per passenger…
- Costs, rows 33–40: EBITDAR, EBITDAR margin, EBITDA, EBITDA margin…
- Costs, rows 43–49: Total operating costs, Cost per ASK (CASK), Fuel per ASK, CASK ex-fuel…
What a reviewer looks for
- Every cost driven from ASK, so a longer stage length looks no cheaper per seat kilometre.
- CASK compared across airlines without stripping fuel.
- Yield read as the fare, without the distance flown.