GA SMA TOOK OFF 20 MINS BEFORE SUNSET FOR 1 LAST SUNSET PARACHUTE JUMP IN AN ACFT CERTIFICATED DAY VFR ONLY.

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IT WAS THE LAST JUMP OF THE DAY; THE COVETED 'SUNSET JUMP' AND THE 5 SKYDIVERS WERE TAKING LONGER THAN USUAL TO GET TO THE PLANE. I DECIDED TO REVIEW MY SHORT FIELD PROCS; REQUIRED RWY LENGTHS; VERT SPDS. THEY ARRIVED AT XA40 AND I TAXIED MIDFIELD FOR TKOF. THE SMA REQUIRED 2800 FT TO CLR A 50 FT OBSTACLE (TREES; FOR ME) AND I HAD 4500 FT AHEAD AND THE PLANE HAD BEEN RUNNING STRONG AND COOL ALL DAY. I THOUGHT IT WAS A FAIRLY SAFE DECISION. WE WERE CLBING THROUGH 4000 BEFORE I STARTED TO HAVE DOUBTS. SUNSET WAS AT XB00 AND I HAD TO DROP THEM AS HIGH AS I COULD AND STILL GET DOWN AND PARKED BY SUNSET AS THE ARPT IS UNLIGHTED. ALL OF A SUDDEN CLOUDS; TWRING CUMULUS; WERE ROLLING IN GETTING TALLER AND FASTER (TOWARDS THE RWY) AT AN UNUSUAL RATE. THERE WERE 2 PLANES ABOVE ME DOING THE SAME THING FOR THEIR JUMPERS AND INSTEAD OF ASKING FOR A WX RPT/TOPS AT 11000 FT THEIR ALT; I DECIDED THAT IF THEY WERE OPERATING THEN THERE MUST BE LEGAL HOLES UP THERE SOMEWHERE. I ALSO FIGURED THAT IT WAS MOVING SO FAST THAT BY THE TIME I WAS AT 7000 (MY ESTIMATE TO MAKE MY LNDG LEGAL) IT WOULD HAVE CLRED. THE OTHER 2 PLTS (FRIENDS) HEARD ME CLBING AND DIDN'T ISSUE ANY CAUTION -- ANOTHER ASSUMPTION THAT IT WOULD BE OK. BY 7000 FT ALL MY ASSUMING HAD PUT ME IN AN UNCOMFORTABLE POS. I MADE 1 PASS OVER THE DROP ZONE AND THE JUMPERS SAID CLOUDS WERE THERE BUT MOVING FAST AND TO GAR FOR A SECOND TRY. I KNEW THIS FLT WAS TIGHT BUT I FELT BAD FOR THEM AND DID A QUICK GAR. CLOUD CLRNC WAS STILL ILLEGAL AND I STARTED DSNDING IMMEDIATELY. I THOUGHT I COULD DROP THEM OUT AT 2000 FT (BASE 2600 FT) AS I FLEW A PATTERN FOR RWY 8 (WINDS ENE 20-30 HIGHER) BUT AS I DSNDED BELOW THE CLOUDS I COULD SEE THAT THE SUN HAD ALMOST SET AND DARKNESS HAD FALLEN. I TOLD THEM TO TIGHTEN THEIR SEATBELTS AS I WAS GOING TO DSND FOR RWY 26 AS IT WOULD BE FASTER -- NO TIME FOR JUMPING. AT 1500 MY WINDSHIELD STARTED TO FOG UP; I REALIZED MY LNDG LIGHT HAD GONE OUT AND IT WAS HARD TO SEE THE RWY WITH NO DEPTH PERCEPTION/LIGHTING ANYWHERE. I ADVISED MY PAX THAT IT MIGHT BE A HARD LNDG AND TO HOLD ON. WE LANDED LONG WITH THE TAILWIND AND WE TAXIED TO THE RAMP WITHOUT INCIDENT. LOOKING UP; ALL THE CLOUDS HAD LEFT THE AREA -- CLR SKIES; SUN DOWN; STARS STARTING TO PEEK OUT AT XB08. WHAT CAUSED THE PROBLEM? ME. IF I HADN'T BEEN SO EXCITED TO GET MY JUMPERS OUT FOR THEIR SPECIAL JUMP; I COULD HAVE SEEN THE WARNING SIGNS. I HAD 2 PLTS ABOVE ME THAT COULD HAVE TOLD ME WX WAS CLOSING IN AND I COULD HAVE LET THEM OUT AROUND 4000 FT. ALSO; SINCE THE ACFT WAS DAY VFR ONLY; I ONLY CHKED THE LIGHTS AT THE BEGINNING OF EACH MONTH. I NEVER THOUGHT I'D ACTUALLY NEED THEM. I ALSO FOUND ON THE GND THAT THE BEACON HAD GONE OUT. LASTLY; THE WINDSHIELD FOGGING UP WOULDN'T HAVE BEEN AS BIG A PROBLEM IF I HAD CLEANED THE WINDSHIELD THAT MORNING. ALL I WAS THINKING WAS HOW HIGH I COULD LEGALLY GET MY SKYDIVERS. JUST BECAUSE THEY DON'T PAY ME ON THE GND DOESN'T MEAN THAT I CAN BE LAZY OR NEGLECTFUL ON THE GND (LIGHTS; WINDSHIELD).