Compensation is due. Staffing is the airline's own responsibility.
Check your flightA missing crew member, a crew that has run out of legal duty hours, or a roster that did not work out is the airline's own problem. Staffing an aircraft is part of running an airline, so a delay or cancellation caused by crew shortage is not an extraordinary circumstance and compensation is payable.
The same applies to the most common cause of all, which airlines describe in various ways: the inbound aircraft arrived late. A knock-on delay from an earlier rotation is the airline's responsibility, because how tightly it schedules its fleet is its own commercial decision.
There is one thing to check. If the original delay in that chain was itself caused by something extraordinary, such as a storm earlier in the day, the airline may be able to carry that defence through to your flight. It has to prove the connection, and the further down the day your flight sits, the harder that gets.
Compensation is a flat amount set by distance, not by ticket price: €250 up to 1,500 km, €400 for longer flights inside the EU and for 1,500–3,500 km, and €600 beyond 3,500 km. The UK equivalents are £220, £350 and £520.
Distance is measured in a straight line from your original departure airport to your final destination, which on a connecting itinerary often lands you in a higher band than you would expect.
Duty of care is separate from compensation and does not depend on the cause. Once you are delayed two hours or more the airline owes you meals and drinks, two phone calls, and a hotel plus transfers if you are stuck overnight. This applies in bad weather, during ATC strikes, and in every other situation where no compensation is payable.
Airlines frequently provide none of this during major disruption. Buy your own, keep every receipt, and claim the cost back afterwards.
Work out what you are owed