Search and rescue teams are hunting the Adriatic Sea for the F-16 fighter jet that went missing after it left the Aviano air base in northern Italy.
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The paralympian posted a time of two minutes and 57 seconds on Sunday.
The 17-year-old posted a supportive Instagram message accompanied by a childhood photo.
"Big Sam" was spotted letting his hair down in the seaside resort weeks after securing Premier League survival for Sunderland.