Gate card: KLM Royal Dutch Airlines (KL)

The airline's policy: “Flying as a passenger of size (KLM's own page title); extra seat sold as an 'additional adjacent seat'”

KLM frames the extra seat as optional, not mandatory: 'For those who prefer more personal space, we offer the option to purchase an additional adjacent seat at a discounted rate.' The page also publishes armrest spacing and belt lengths so passengers can self-assess, and notes you need to be able to move your seat's armrests up and down. Separately, KLM sells check-in-time comfort products ('Empty Seat' to block adjacent seats, and 'My Extra Space' to block your whole row).

Refunds: Not published for the customer-service-arranged additional seat. For the 'Empty Seat'/'My Extra Space' check-in products, KLM states you automatically get a refund if the seat is needed to accommodate other passengers or becomes unavailable for operational reasons.