A formal compensation letter for a cancelled flight in 2026 should be concise and strictly reference EC 261/2004 (EU) or UK 261 regulations. The letter must include your Booking Reference (PNR), flight number, and the date of the incident. It should state: "I am writing to formally request compensation for flight [Number] on [Date], which was cancelled with less than 14 days' notice. Under Regulation EC 261/2004, I am entitled to €[Amount, e.g., 250, 400, or 600] based on the flight distance of [KM]." You should also attach copies of your boarding pass and receipts for any "Duty of Care" expenses you incurred, such as meals or hotel stays that the airline failed to provide. A high-value peer tip: explicitly state that the cancellation was not due to "extraordinary circumstances" if you know the cause was mechanical or crew-related. By providing a clear "paper trail" and a direct demand for payment to your IBAN or bank account, you signal to the airline's legal team that you are a "knowledgeable traveler" who won't be deterred by a standard automated rejection.