Recent study has sorted out few reasons behind why are we scared of Friday the 13th.

It was also reported that another reason behind this belief is that Friday used to be called hanging day as it was customary to execute criminals on this day. There were 13 steps up to the scaffold, 13 turns in a hangman's noose and 13 pence and a halfpenny paid to the hangman.
According to Flight comparison website Jetcost.co.uk, flight inquiries for this particular day dropped by up to 27 percent as people are frightened to travel in aeroplanes on Friday the 13th.
Meanwhile, insurance company Norwich Union revealed that they received more accident claims for Friday the 13th than on any other day.
It has also been revealed that more murders are committed on Friday the 13th.
Source-ANI