Neither pilot held an instrument rating or IMC qualification. The right seat pilot held a night rating.
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Passengers who had flown with the pilots on a previous trip to Le Touquet reported that they had briefly entered cloud during that flight, but on that occasion the aircraft had continued without incident.
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gradual normalization of a risky situation under the assumption that entering a cloud is no big deal, beacuse "I have done it earlier without any problems.".