SINGAPORE: Singapore Airlines (SIA) said on Thursday its full-year net profit more than doubled on higher income from investments and reduced losses from associate companies as fuel expenses fell due to lower oil prices. A refund for a fine paid by the carrier’s cargo arm in the previous financial year also bolstered earnings, but the airline said the competitive environment remained ‘challenging’ due to weak global economic growth and expanding capacity. Group net profit for the year ending March 31 came in at 804.4 million Singapore dollars ($587 million), up 118.5 per cent from the year before. Revenue eased 2.2 per cent to 15.23 billion Singapore dollars, SIA said in a filing with the Singapore Exchange.