Narrative:

The line attendant pulled the caravan from the hangar for an XA35 scheduled departure. Rain changes to light snow as the aircraft is chocked. Outside air temperature was 34 degrees F. Snow melted upon contact. XA20 truck arrives. Crew begins loading the aircraft. Outside air temperature now 32 degrees F. About 1/4 inch of very wet slush has accumulated on the ground and on the aircraft. Line attendant swept wings clean, I removed slush from windscreen. XA30 ATIS was advertising runway 28R for departure. Normally, I use runway 28L because it sits immediately adjacent to the ramp. However, runway 28L is 3800 ft in length versus 10528 ft runway 28R. In light of the deteriorating WX, I decided I would request the longer runway. (I had taxied to runway 28R perhaps 3 times in the last 2 yrs, never at night.) ground frequency and tower frequency were being handled by the same operator, and I had been monitoring both frequencys for about 2 mins. It sounded to me like tower was trying to re-establish contact with a VFR pilot who was now flying in what was virtually an IFR environment at night. I wondered if I should intrude on ground frequency at which I perceived as a high stress/high workload time for the lone controller. Eventually, I called for clearance and taxi instructions, and was instructed to taxi to runway 28R. However, no taxi routing was given. At XA35, I turned on the taxi light, signaling the marshaler that I was ready to leave, and discovered that slush had obstructed my forward vision. In addition to this outside impediment, condensation covered the inside of the windscreen, which I wiped clean. The application of windscreen de-ice gave me a small field of vision through the heat plate, and I taxied about 100 yards to taxiway G. I was still having a hard time seeing. I stopped the aircraft and ran up the engine, blowing slush from the windscreen. The inside of the windscreen collected more condensation, which was wiped away, but the defrost provision proved most ineffective, and manual wiping would continue until takeoff. At XA36, I know taxiway J had been closed due to construction, but decided to get a confirmation from ground that I was cleared to runway 28R via taxiway G, taxiway F, and taxiway a. Ground responded in the affirmative. This was a double mistake. Taxiway F should not be a part of the taxi route. I do not know why I didn't catch this, but I didn't. I can only speculate as to why ground approved an erroneous request. His plate was full with the missing airborne aircraft. At XA37, I reached the intersection of taxiway G, taxiway TA, and runway 7/25, and made an 80 degree right turn onto what I thought was taxiway a. It should have been a 120 degree turn. I was on runway 7/25. Ground recognized the situation and instructed me to exit at taxiway F, which I did. Runway 7/25 was not the active runway at the time, but I believe this would still be considered a runway incursion. I believe this incident occurred because: 1) my attention was distraction by the events surrounding a possible missing aircraft, 2) I could not see very well due to snow, interior condensation and night condition, 3) the turn point from taxiway G to taxiway a is shared by an intersecting runway, and 4) I was confused over the wrongly requested and wrongly assigned taxi instructions regarding taxiway F.

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Original NASA ASRS Text

Title: C208 PLT HAS RWY INCURSION AT BIL.

Narrative: THE LINE ATTENDANT PULLED THE CARAVAN FROM THE HANGAR FOR AN XA35 SCHEDULED DEP. RAIN CHANGES TO LIGHT SNOW AS THE ACFT IS CHOCKED. OUTSIDE AIR TEMP WAS 34 DEGS F. SNOW MELTED UPON CONTACT. XA20 TRUCK ARRIVES. CREW BEGINS LOADING THE ACFT. OUTSIDE AIR TEMP NOW 32 DEGS F. ABOUT 1/4 INCH OF VERY WET SLUSH HAS ACCUMULATED ON THE GND AND ON THE ACFT. LINE ATTENDANT SWEPT WINGS CLEAN, I REMOVED SLUSH FROM WINDSCREEN. XA30 ATIS WAS ADVERTISING RWY 28R FOR DEP. NORMALLY, I USE RWY 28L BECAUSE IT SITS IMMEDIATELY ADJACENT TO THE RAMP. HOWEVER, RWY 28L IS 3800 FT IN LENGTH VERSUS 10528 FT RWY 28R. IN LIGHT OF THE DETERIORATING WX, I DECIDED I WOULD REQUEST THE LONGER RWY. (I HAD TAXIED TO RWY 28R PERHAPS 3 TIMES IN THE LAST 2 YRS, NEVER AT NIGHT.) GND FREQ AND TWR FREQ WERE BEING HANDLED BY THE SAME OPERATOR, AND I HAD BEEN MONITORING BOTH FREQS FOR ABOUT 2 MINS. IT SOUNDED TO ME LIKE TWR WAS TRYING TO RE-ESTABLISH CONTACT WITH A VFR PLT WHO WAS NOW FLYING IN WHAT WAS VIRTUALLY AN IFR ENVIRONMENT AT NIGHT. I WONDERED IF I SHOULD INTRUDE ON GND FREQ AT WHICH I PERCEIVED AS A HIGH STRESS/HIGH WORKLOAD TIME FOR THE LONE CTLR. EVENTUALLY, I CALLED FOR CLRNC AND TAXI INSTRUCTIONS, AND WAS INSTRUCTED TO TAXI TO RWY 28R. HOWEVER, NO TAXI ROUTING WAS GIVEN. AT XA35, I TURNED ON THE TAXI LIGHT, SIGNALING THE MARSHALER THAT I WAS READY TO LEAVE, AND DISCOVERED THAT SLUSH HAD OBSTRUCTED MY FORWARD VISION. IN ADDITION TO THIS OUTSIDE IMPEDIMENT, CONDENSATION COVERED THE INSIDE OF THE WINDSCREEN, WHICH I WIPED CLEAN. THE APPLICATION OF WINDSCREEN DE-ICE GAVE ME A SMALL FIELD OF VISION THROUGH THE HEAT PLATE, AND I TAXIED ABOUT 100 YARDS TO TXWY G. I WAS STILL HAVING A HARD TIME SEEING. I STOPPED THE ACFT AND RAN UP THE ENG, BLOWING SLUSH FROM THE WINDSCREEN. THE INSIDE OF THE WINDSCREEN COLLECTED MORE CONDENSATION, WHICH WAS WIPED AWAY, BUT THE DEFROST PROVISION PROVED MOST INEFFECTIVE, AND MANUAL WIPING WOULD CONTINUE UNTIL TKOF. AT XA36, I KNOW TXWY J HAD BEEN CLOSED DUE TO CONSTRUCTION, BUT DECIDED TO GET A CONFIRMATION FROM GND THAT I WAS CLRED TO RWY 28R VIA TXWY G, TXWY F, AND TXWY A. GND RESPONDED IN THE AFFIRMATIVE. THIS WAS A DOUBLE MISTAKE. TXWY F SHOULD NOT BE A PART OF THE TAXI RTE. I DO NOT KNOW WHY I DIDN'T CATCH THIS, BUT I DIDN'T. I CAN ONLY SPECULATE AS TO WHY GND APPROVED AN ERRONEOUS REQUEST. HIS PLATE WAS FULL WITH THE MISSING AIRBORNE ACFT. AT XA37, I REACHED THE INTXN OF TXWY G, TXWY TA, AND RWY 7/25, AND MADE AN 80 DEG R TURN ONTO WHAT I THOUGHT WAS TXWY A. IT SHOULD HAVE BEEN A 120 DEG TURN. I WAS ON RWY 7/25. GND RECOGNIZED THE SIT AND INSTRUCTED ME TO EXIT AT TXWY F, WHICH I DID. RWY 7/25 WAS NOT THE ACTIVE RWY AT THE TIME, BUT I BELIEVE THIS WOULD STILL BE CONSIDERED A RWY INCURSION. I BELIEVE THIS INCIDENT OCCURRED BECAUSE: 1) MY ATTN WAS DISTR BY THE EVENTS SURROUNDING A POSSIBLE MISSING ACFT, 2) I COULD NOT SEE VERY WELL DUE TO SNOW, INTERIOR CONDENSATION AND NIGHT CONDITION, 3) THE TURN POINT FROM TXWY G TO TXWY A IS SHARED BY AN INTERSECTING RWY, AND 4) I WAS CONFUSED OVER THE WRONGLY REQUESTED AND WRONGLY ASSIGNED TAXI INSTRUCTIONS REGARDING TXWY F.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.