Narrative:

I was departing sfo on the afternoon of jul/xa/99. The WX at the takeoff end was clear, and the WX at the departure end and to the west was 1200 ft overcast with 10 mi visibility. I was given a VFR clearance to turn right to a 350 degree heading and to remain at or below 2000 ft. That heading would keep me clear of the overcast layer. Shortly after takeoff and the turn towards 350 degrees, the tower told me to 'keep the highway on your right.' I was confused because the first highway I saw had a hill to its left that I would have hit because it was covered by the stratus layer. I saw another highway going west under the overcast that I could keep on my right. I then asked the tower if he still wanted me on a 350 degree heading and he said no. I then followed the wbound highway to the west. The tower had expected me to follow a different highway and called when he saw I was wbound. He then had some difficulty arranging a handoff because the overcast had me at 1000 ft and below his radar coverage. Because of an ambiguous instruction and my failure to adequately clarify it, I didn't do what the tower expected of me. I had done this procedure scores of times in the past and had been switched to a wbound heading before but had never been asked to follow a highway, so I was somewhat surprised by the instruction. I tried to follow the instruction to follow the highway while ensuring my own safety by not coming too close to the terrain. My response when I was confused should have been that I didn't understand what was expected of me and then that I couldn't comply because of the cloud cover.

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Original NASA ASRS Text

Title: A COMMERCIAL RATED PLT FLYING A TWIN ENG TURBOPROP CHARTER FROM SFO DEPARTS VFR AND IS UNABLE TO MAINTAIN THE CLRNC THAT ATC ISSUED.

Narrative: I WAS DEPARTING SFO ON THE AFTERNOON OF JUL/XA/99. THE WX AT THE TKOF END WAS CLR, AND THE WX AT THE DEP END AND TO THE W WAS 1200 FT OVCST WITH 10 MI VISIBILITY. I WAS GIVEN A VFR CLRNC TO TURN R TO A 350 DEG HDG AND TO REMAIN AT OR BELOW 2000 FT. THAT HEADING WOULD KEEP ME CLR OF THE OVCST LAYER. SHORTLY AFTER TKOF AND THE TURN TOWARDS 350 DEGS, THE TWR TOLD ME TO 'KEEP THE HWY ON YOUR R.' I WAS CONFUSED BECAUSE THE FIRST HWY I SAW HAD A HILL TO ITS L THAT I WOULD HAVE HIT BECAUSE IT WAS COVERED BY THE STRATUS LAYER. I SAW ANOTHER HWY GOING W UNDER THE OVCST THAT I COULD KEEP ON MY R. I THEN ASKED THE TWR IF HE STILL WANTED ME ON A 350 DEG HDG AND HE SAID NO. I THEN FOLLOWED THE WBOUND HWY TO THE W. THE TWR HAD EXPECTED ME TO FOLLOW A DIFFERENT HWY AND CALLED WHEN HE SAW I WAS WBOUND. HE THEN HAD SOME DIFFICULTY ARRANGING A HDOF BECAUSE THE OVCST HAD ME AT 1000 FT AND BELOW HIS RADAR COVERAGE. BECAUSE OF AN AMBIGUOUS INSTRUCTION AND MY FAILURE TO ADEQUATELY CLARIFY IT, I DIDN'T DO WHAT THE TWR EXPECTED OF ME. I HAD DONE THIS PROC SCORES OF TIMES IN THE PAST AND HAD BEEN SWITCHED TO A WBOUND HEADING BEFORE BUT HAD NEVER BEEN ASKED TO FOLLOW A HWY, SO I WAS SOMEWHAT SURPRISED BY THE INSTRUCTION. I TRIED TO FOLLOW THE INSTRUCTION TO FOLLOW THE HWY WHILE ENSURING MY OWN SAFETY BY NOT COMING TOO CLOSE TO THE TERRAIN. MY RESPONSE WHEN I WAS CONFUSED SHOULD HAVE BEEN THAT I DIDN'T UNDERSTAND WHAT WAS EXPECTED OF ME AND THEN THAT I COULDN'T COMPLY BECAUSE OF THE CLOUD COVER.

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.