UK Stocks-Factors to watch on Sept 22

Sept 22 (Reuters) - Britain's FTSE 100 index is seen opening down 23 points at 7,241.1 on Friday, according to financial bookmakers. * RIO TINTO: Flush with cash, Rio Tinto said it would buy back an additional $2.5 billion worth of its shares, dishing out the proceeds from a sale of coal assets earlier than some had expected. * RYANAIR: Ryanair boss Michael O'Leary on Thursday scrambled to placate pilots and reassure investors as the airline's annual general meeting was dominate