▁work ▁on ▁a ▁major ▁upgrade ▁programme ▁on ▁the ▁Douglas ▁A - 4 S ▁Sky h awk ▁attack ▁aircraft ▁then ▁in ▁service ▁with ▁the ▁Republic ▁of ▁Singapore ▁Air ▁Force ▁( RS AF ). ▁Refer red ▁to ▁as ▁the ▁A - 4 SU ▁Super ▁Sky h awk , ▁the ▁modification ▁package ▁involved ▁replacing ▁the ▁original ▁Wright ▁J 6 5 ▁tur bo jet ▁engine ▁with ▁a ▁non - after burn ing ▁model ▁of ▁the ▁newer ▁General ▁Electric ▁F 4 0 4 - GE - 1 0 0 D ▁tur bo fan ▁engine , ▁along ▁with ▁a ▁complete ▁modern isation ▁of ▁the ▁av ion ics ▁suite ▁and ▁additional ▁equipment ▁being ▁installed , ▁including ▁a ▁P ave ▁Pen ny ▁las er ▁see ker , ▁an ▁In ert ial ▁navigation ▁system ▁( IN S ), ▁a ▁T act ical ▁air ▁navigation ▁system ▁( TAC AN ), ▁fore ▁& ▁a ft ▁Rad ar ▁warning ▁rece ivers ▁( R WR ) ▁and ▁ch aff / f lare ▁counter me asures ) ▁of ▁the ▁aircraft . ▁The ▁F 4 0 4 ▁engine ▁provided ▁ 2 9 % ▁more ▁thrust , ▁resulting ▁in ▁a ▁ 3 0 % ▁reduction ▁in ▁take off ▁time ▁as ▁well ▁as ▁an ▁increase ▁in ▁us able ▁payload , ▁range ▁and ▁maximum ▁speed ▁of ▁ ▁at ▁sea ▁level . ▁In ▁total , ▁approximately ▁ 1 5 0 ▁air frames ▁( all ▁A - 4 B s ▁and ▁Cs ) ▁were ▁acquired ▁by ▁Singapore . ▁ ▁Since ▁the ▁ 1 9 9 0 s , ▁ST ▁A eros pace ▁has