Recently I was asked to comment on the Latvian TV show “Bez Tabu” about the practice of the airlines on changing the aircraft. A fragment of that interview can be seen here.
Usually, per T&C of the airline, they reserve the right to change aircraft type (or even have another airline service the flight per wet lease). In this case, no compensation can be requested, but some airlines offer discount vouchers for future flights.
In case additional pre-purchased services where not delivered, such as meal, seating, the passengers can request a refund.
In the flight is delayed, per EC regulation passengers can claim compensation. I have described in detail how to do this here.
