▁div v ied ▁up ▁across ▁its ▁routes ▁according ▁to ▁many ▁different ▁method ologies — by ▁the ▁number ▁of ▁fl ights ▁on ▁that ▁route ▁during ▁that ▁time ▁period , ▁by ▁the ▁number ▁of ▁flight ▁hours ▁on ▁that ▁route , ▁etc . ▁There ▁is ▁not ▁necessarily ▁any ▁right ▁method ▁for ▁making ▁such ▁cost ▁alloc ations , ▁but ▁it ▁is ▁important ▁when ▁making ▁compar isons ▁across ▁air lines ▁that ▁if ▁an ▁allocation ▁method ology ▁is ▁relevant ▁( i . e . ▁less ▁than ▁the ▁entire ▁of ▁each ▁air line ▁is ▁being ▁compared ) ▁then ▁the ▁same ▁allocation ▁method ology ▁is ▁used ▁with ▁each ▁air line ▁being ▁compared . ▁ ▁For ▁a ▁simple ▁example ▁of ▁the ▁calculation ▁of ▁C AS M , ▁in ▁the ▁second ▁quarter ▁of ▁ 2 0 1 1 , ▁South west ▁Airlines ▁( including ▁its ▁Air T ran ▁Air ways ▁subs idi ary ) ▁had ▁operating ▁costs ▁of ▁$ 3 . 9 2 9 ▁b n ▁and ▁ 3 1 . 4 5 7 ▁b n ▁AS M s , ▁as ▁reflected ▁in ▁South west ' s ▁SE C ▁Form ▁ 1 0 - Q ▁for ▁that ▁period . ▁South west ' s ▁system ▁C AS M ▁for ▁the ▁second ▁quarter ▁of ▁ 2 0 1 1 ▁was ▁then : ▁▁▁▁▁▁▁▁▁▁▁▁ ▁C AS M ▁= ▁Direct ▁Oper ating ▁Cost ▁/ ▁Av ailable ▁Se at ▁M ile ▁= ▁$ 3 . 9 2 9 ▁billion ▁/ ▁ 3 1 . 4 5 7 ▁billion ▁= ▁ 1 2 . 4 9 ▁c ents ▁