One excuse that is used a lot is that the plane can’t be de-iced. A scenario in which a flight is cancelled because the temperatures fall below zero and there is no de-icing agent was often declared as “extraordinary circumstances” by the airlines in the past. Fortunately, court judgments are now available holding the airline responsible for the lack of de-icing. Airlines have to have a sufficient supply of de-icing agent available and use it in good time to ensure that flights can run to schedule. Often, weather-related delays also mean that the crew members end up exceeding the maximum permitted working hours, which is why flights are cancelled. Again, these are not extraordinary circumstances and passengers are entitled to compensation.Extreme weather conditions almost always release the airlines from their obligation to pay compensation. There are, however, a few special cases in which passengers have received compensation. The following judgments were made in passengers’ favour.

• Anti-freeze: Airlines have to have enough anti-freeze or de-icing agent on hand to cope with heavy snowfall or sleet. If a flight is significantly delayed because there is no de-icing agent or the de-icing process took a considerable length of time, then this cannot be described as “extraordinary circumstances". Passengers are entitled to compensation. These conditions are based on the Local Court (Amtsgericht) of Frankfurt confirmed previous court decisions (judgment of 22 May 2015, case ref.29 C 286/15 [85]).

Cannot find a link to the case....interesting reading I am sure though. Follow up is interest sake rather than compensation as I appreciate a de iced plane is a safe plane.