Their international competitors may be cheering tumbling oil prices, but the collapse in the ruble has meant major financial turbulence for Russian airlines who have expenses in foreign currencies, AFP reported. The ruble has slumped by 40% this year against the dollar and euro, mostly due to crude oil prices falling by half in the past six months as Russia’s economy is heavily dependent upon oil exports. As jet fuel accounts for upwards of a quarter of the cost for flights, most airlines are set to see a boost to earnings.