A B737NG'S AFT CARGO DOOR LIGHT ILLUMINATED AFTER TKOF. THE FLT RETURNED TO LAND OVERWEIGHT.

Narrative

TKOF WAS UNEVENTFUL UNTIL APPROX 500-1000 FT AGL WHEN THE MASTER CAUTION DOORS LIGHT ILLUMINATED; WITH THE AFT CARGO DOOR LIGHT ILLUMINATED ON THE OVERHEAD PANEL. THE DEP WAS FLOWN ON A 142 DEG HDG; WHILE CLBING TO A MODIFIED ALT OF 3000 FT MSL. THE DOOR ANNUNCIATOR CHKLIST IN THE QRH WAS ACCOMPLISHED FOLLOWED BY THE AFTER TKOF CHKLIST. AFTER CONSIDERING THE LACK OF SUITABLE ALTERNATES; THE NARROWING WINDOW OF GOOD RECOVERY WX IN ZZZ AND THE RISKS INVOLVED IN CONTINUING TO CLB TO A HIGHER ALT TO FURTHER VERIFY THE NORMAL OP OF THE PRESSURIZATION SYS; THE DECISION WAS MADE TO ACCOMPLISH AN OVERWT LNDG BACK TO ZZZ. A REQUEST WAS MADE FOR AN ILS TO RWY XXL; BUT ATC STATED IT WAS UNAVAILABLE DUE TO IT BEING USED TO PARK DEP DELAYED ACFT. AN ILS TO RWY XYL USING A 40 DEG FLAP; COUPLED APCH; TO A HAND FLOWN UNEVENTFUL LNDG WAS ACCOMPLISHED. NO FLAP 40 KT PLACARD SPDS WERE EXCEEDED. THE LNDG WAS ACCOMPLISHED AT A GROSS WT OF APPROX 158000 LBS WITH A SINK RATE OF APPROX 500 FPM. AN AFTER LNDG CHK AND UNEVENTFUL TAXI BACK TO THE GATE WAS THEN ACCOMPLISHED. THE AFT CARGO DOOR CAUTION LIGHT REMAINED ILLUMINATED UNTIL AFTER ENG SHUTDOWN AT THE GATE. WE WROTE UP THE OVERWT LNDG IN THE LOGBOOK.