What (a) percentage of South Africa’s aviation fleet was grounded in terms of rules and regulations implemented by the Civil Aviation Authority on (i) 31 March 2013, (ii) 30 September 2012, (iii) 31 March 2012 and (iv) 31 March 2011, (b) were the reasons for the grounding of the aircraft on each date and (c) percentage of aircraft on each date were grounded for safety considerations?