Singapore Airlines said it will be vigilant on costs as it warned yet again that the weak operating outlook is likely to persist amid excess capacity and aggressive pricing by competitors. The prospects in most major economies remain “tepid,” while passenger airline business continued to be impacted by geopolitical uncertainty and weak global economic conditions, Singapore Air said Thursday. The premium carrier reported its first quarterly slump in two years, saying passenger and cargo yields -- a key measure of profitability in the industry -- continue to be under stress. Singapore Air and its other premium rival Cathay Pacific are fighting to revive profit growth as Middle Eastern carriers, offering comforts such as in-flight shower, lure first- and business-class passengers away, while budget carriers chip away at the economy end. Both the Asian airlines have warned of tougher days ahead, while Cathay said last month that it is conducting a “critical review” of its business after scrapping its profit outlook. “How they arrest the declining yields will be the key issue for Singapore Airlines,” said Shukor Yusof, founder of aviation consulting firm Endau Analytics. “Singapore Air faces extreme competition and is suffering as much as Cathay. They are banking on flights to the US going forward.” Singapore Air said Thursday that net income tumbled 70% to S$64.9m (US$46.8m) in the three months through September from a year earlier. Sales fell about 5% to S$3.65b. The yield dropped 3.8% to 10 cents in the quarter.<br/>