ICING FROST FORMING ON WINGS DURING GND LAYOVER.

Narrative

THE ACFT; A B-757; HAD FLOWN IN TO PIT FROM SFO; ON A RED-EYE. IT HAD BEEN CLEANED; SVCED AND A MAINT TRANSIT CHK HAD BEEN APPLIED TO THE ACFT. IT HAD BEEN ON THE GND FOR ABOUT AN HR. THE WX WAS CLR; CALM WINDS; WITH A TEMP OF 26 DEGS F. THE FO RPTED THAT THE PREFLT WALK AROUND CHK HAD BEEN COMPLETED SATISFACTORILY! THE ACFT WAS RPTED 'OK' FOR FLT! AS WE TAXIED OUT FOR OUR FLT TO DCA; THE FLT ATTENDANT CAME FORWARD AND RPTED THAT ONE OF 'OUR' DEADHEADING PLTS RPTED SOME FROST/ICE CONTAMINATION ON TOP OF THE WING. I SENT THE FO BACK TO INSPECT THE WINGS; AND HE RETURNED; INDICATING THAT THERE WERE TRACES OF ICE/FROST NOW FORMING OVER THE TOP OF WING; BUT THAT THE LEADING EDGES REMAINED TOTALLY CLEAN. I DECIDED TO PROCEED TO THE DEICING STATION; AND GET THE FROST REMOVED (PROBABLY A RESULT OF A COLD-SOAKED WING; FREEZING CONDENSATION FORMED WHEN THE ACFT WAS FUELED). WE DEPARTED UNEVENTFULLY WITH A SAFE TRIP TO DCA! RECOMMENDATIONS: 1) APPLY TYPE I FLUID ANY TIME THE TEMP IS BELOW 32 DEGS F/0 DEGS C; EVEN THOUGH IT IS CLR WITH A LOW TEMP/DEWPOINT. 2) REQUIRE A PRE-TKOF CONTAMINATION CHK; ANY TIME THE TEMP IS BELOW 50 DEGS F/10 DEGS C; EVEN IN CLR WX CONDITIONS! IN OUR CASE; FROST BEGAN TO FORM ON TAXI OUT TO THE RWY. IT CAN HAPPEN IN CLR WX CONDITIONS; WITH A LOW DEWPOINT! 3) CURRENT COMPANY PROC IS TO ONLY DO A PRE-TKOF CONTAMINATION CHK; IF THE CONDITION(S) EXIST! ANY TIME THE TEMP IS BELOW 32 DEGS F/0 DEGS C; REGARDLESS OF NO PRECIPITATION OR CLR SKIES; A PRE-TKOF CHK SHOULD BE REQUIRED!