[EXPRESS.CO.UK] They coded their language with musical references, often referring to “hits”. The conversation included boasts that a song would “climb up the charts” – a veiled reference to increases in jihadi recruits once the attacks had been launched.

It is thought the pilots were preparing to smuggle in explosive devices or chemical weapons. The messages were intercepted as they flew from a European airport, thought to be Schiphol, in Amsterdan, to Middle Eastern destinations.

They were unaware that Channel 121, the Mayday channel used to broadcast emergencies, was being monitored.
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It is believed that at least one of the airlines involved had already been placed on a UK aviation watchlist.