Detailed Instructions: Given a travel related situation, and given a specific question about the situation, summarize the question into a title
Q: Today I've received the following email from Air France in regards to my request for compensation under EU flight delay rules:

We are really sorry to learn our flight AF379 delay on 15th August 2018 disrupted your travel plans. We understand that delays inconvenience our passengers, so we do all we can to limit them. However, we sometimes face extraordinary circumstances when Air Traffic Control delays a flight's departure or arrival. These Air Traffic Control delays are beyond our control.

As you may be aware, compensation is laid down and paid in accordance with the EC regulation 261/2004. In line with this regulation - and our General Conditions of Carriage - I must respectfully decline your request for compensation on this occasion. I am sorry for any disappointment this may cause.

How can I verify if ATC is in fact the cause for the delay of my flight?

A:
How can I verify if an airline is telling the truth about the reason for the flight's delay, in the context of EU delay compensation?