In order to become a pilot, should an individual have an above average mathematical ability?
In short, no.

To quote Patrick Smith, veteran pilot and author of Cockpit Confidential and the blog  "Ask the Pilot," 


  There's a lingering assumption that airline pilots are required to demonstrate some sort of Newtonian genius before every takeoff- a vestige, maybe, from the days when airmen carried slide rules and practiced celestial navigation... 
  The basics are what pilots encounter. Routine arrival assignments require some quickie mental arithmetic.


So basically, it doesn't involve super complex math. You need to be able to do some moderate arithmetic and geometry, but nothing so complex that it can't be done, as Smith says, on 


  my $6.95 calculator from CVS- the one flight-bag accessory more indispensable than an emergency checklist, aircraft deicing guide, or a bag of ramen noodles.