how many times has an areoplane got hit with lighting?

Question: how many times has an areoplane got hit with lighting?
- Keywords:
  aeroplane,
  hit,
  lightning,
  plane,
  times
Asked by pricej to rhysphillips on 11 Jun 2011. This question was also asked by 07martindev.
- Rhys Phillips answered on 11 Jun 2011:
  
  Each commercial aeroplane (the ones you’d use for your holiday) is hit by lightning approximately once every year – more often than most people realise!

Question: how many times has an areoplane got hit with lighting?