WX LEGALITY FOR APCH.

Narrative

AFTER A LONG DAY WORKING AS A CFI; I HAD 1 LAST NON- INSTRUCTING FLT FROM PHL TO PTW TO REPOSITION AN ACFT. WE DEPARTED PHL AT APPROX XA00 ON AN IFR PLAN. WX WAS CEILING 600 FT VISIBILITY; 3 MI IN FOG. THE FLT TO PTW WAS UNEVENTFUL. WE BROKE OUT AT ABOUT 1100 FT AND HAD A 3-4 MI VISIBILITY IN FOG. MINIMUMS WERE 820 FT AND 1 MI. PTW IS UNCTLED AND; ON THE GND; I CALLED PHL APCH TO CANCEL IFR. THE CTLR ASKED WHAT THE WX WAS LIKE ON OUR APCH BECAUSE HE HAD ANOTHER ACFT HOLDING FOR THE APCH. I LOOKED AT MY CLIPBOARD AND SAID IT WAS APPROX 600 FT AND 3 MI. THIS OF COURSE WAS THE WRONG WX. THIS WAS THE PHL WX WE HAD GOTTEN ON DEP. I DIDN'T REALIZE MY MISTAKE UNTIL LATER THAT NIGHT WHILE DRIVING HOME. THIS COULD HAVE BEEN A PROB FOR THE PLT HOLDING FOR THE APCH OR OTHER PLTS LNDG AT PTW THAT NIGHT. THEY MIGHT DIVERT THINKING THAT THE WX WAS WORSE THAN IT WAS. LEADING TO THIS MISTAKE WAS A COMMON FACTOR - A VERY LONG DAY AT THE ARPT. AS A CFI; I SPEND ALL DAY AT THE ARPT. I MAY ONLY FLY 4 HRS BUT I AM ON DUTY MAYBE 12 OR 14 HRS. THE REGS SAY 8 HRS OF FLT INSTRUCTIONS; BUT THEY DON'T MENTION DUTY TIME. THERE SHOULD BE MANDATORY REST PERIODS FOR FLT INSTRUCTORS. DUTY HRS (OFFICE-FLT-GND) SHOULD BE KEPT TRACK OF. IT IS TRUE THAT SOME CFI'S WILL DO ANYTHING FOR MONEY; BUT WE MUST POLICE OURSELVES TO AVOID DANGEROUS SITS. ADDING REGS FOR MANDATORY REST PERIODS IS A GOOD STARTING POINT.