Small transport taxied onto active runway without clearance. Visibility was one-eighth mile in fog.

Attributes
ACN	174569
Time
Date	199103
Day	Wed
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : hvn
State Reference	CT
Altitude	agl bound lower : 0 agl bound upper : 0
Environment
Flight Conditions	IMC
Light	Dusk
Aircraft 1
Operator	common carrier : air taxi
Make Model Name	Small Transport, Low Wing, 2 Recip Eng
Flight Phase	ground other : taxi
Flight Plan	IFR
Person 1
Affiliation	Other
Function	flight crew : single pilot
Qualification	pilot : atp pilot : commercial
Experience	flight time last 90 days : 100 flight time total : 1630 flight time type : 220
ASRS Report	174569
Person 2
Affiliation	government : faa
Function	controller : local
Qualification	controller : non radar
Events
Anomaly	incursion : runway non adherence : clearance non adherence : far
Independent Detector	other flight crewa
Resolutory Action	controller : issued new clearance
Consequence	Other
Supplementary
Primary Problem	Flight Crew Human Performance
Air Traffic Incident	Pilot Deviation

Narrative:

Flight plan filed to dud (home base). Began to taxi bush out to runway 2. WX now was 100' and 1/8 mi in fog. This was to be my lowest takeoff ever and I was very upset to boot. After called tower that I was ready, tower changed my takeoff instructions. I challenged them, and after a few conversations back and forth, I began a back-taxi on runway 2. I don't remember the exact words, but I told tower I was back-taxiing. Tower responded that he did not clear me into the runway and asked if I was on the runway. He could not see me and I knew at this point I had misunderstood his takeoff instructions to be cleared for takeoff. I had to tell him that I was indeed on the runway because I felt it was the only safe thing to do. If there was an inbound, there could have been a serious accident. I could have avoided any possible violations by simply taxiing back and telling the tower I was ready, 'at the intersection' tower responded to taxi-back anyway and cleared me for takeoff using, I believe, the words, 'go ahead--now you are already on the runway.' I took off and flew home.

Original NASA ASRS Text

Title: SMT TAXIED ONTO ACTIVE RWY WITHOUT CLRNC. VISIBILITY WAS ONE-EIGHTH MILE IN FOG.

Narrative: FLT PLAN FILED TO DUD (HOME BASE). BEGAN TO TAXI BUSH OUT TO RWY 2. WX NOW WAS 100' AND 1/8 MI IN FOG. THIS WAS TO BE MY LOWEST TKOF EVER AND I WAS VERY UPSET TO BOOT. AFTER CALLED TWR THAT I WAS READY, TWR CHANGED MY TKOF INSTRUCTIONS. I CHALLENGED THEM, AND AFTER A FEW CONVERSATIONS BACK AND FORTH, I BEGAN A BACK-TAXI ON RWY 2. I DON'T REMEMBER THE EXACT WORDS, BUT I TOLD TWR I WAS BACK-TAXIING. TWR RESPONDED THAT HE DID NOT CLR ME INTO THE RWY AND ASKED IF I WAS ON THE RWY. HE COULD NOT SEE ME AND I KNEW AT THIS POINT I HAD MISUNDERSTOOD HIS TKOF INSTRUCTIONS TO BE CLRED FOR TKOF. I HAD TO TELL HIM THAT I WAS INDEED ON THE RWY BECAUSE I FELT IT WAS THE ONLY SAFE THING TO DO. IF THERE WAS AN INBND, THERE COULD HAVE BEEN A SERIOUS ACCIDENT. I COULD HAVE AVOIDED ANY POSSIBLE VIOLATIONS BY SIMPLY TAXIING BACK AND TELLING THE TWR I WAS READY, 'AT THE INTXN' TWR RESPONDED TO TAXI-BACK ANYWAY AND CLRED ME FOR TKOF USING, I BELIEVE, THE WORDS, 'GO AHEAD--NOW YOU ARE ALREADY ON THE RWY.' I TOOK OFF AND FLEW HOME.

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.