C150 pilot misinterps controller's visual navigation reference.

Attributes
ACN	571945
Time
Date	200301
Day	Sun
Place
Locale Reference	navaid : sfo.vor
State Reference	CA
Altitude	msl single value : 1400
Environment
Flight Conditions	VMC
Weather Elements	other
Light	Daylight
Aircraft 1
Controlling Facilities	tower : oak.tower
Operator	general aviation : personal
Make Model Name	Cessna 150
Operating Under FAR Part	Part 91
Flight Phase	cruise : level
Flight Plan	None
Person 1
Affiliation	other
Function	flight crew : single pilot
Qualification	pilot : private pilot : instrument
Experience	flight time last 90 days : 15 flight time total : 1226 flight time type : 80
ASRS Report	571945
Person 2
Affiliation	government : faa
Function	controller : local
Events
Anomaly	non adherence : clearance other spatial deviation
Independent Detector	other controllera
Resolutory Action	controller : issued advisory controller : issued new clearance
Consequence	faa : reviewed incident with flight crew
Supplementary
Problem Areas	Flight Crew Human Performance ATC Human Performance Airspace Structure
Primary Problem	Flight Crew Human Performance

Narrative:

I flew my C150H from sonoma skypark (0q9) to palo alto (pao), ca. The WX was very hazy, with some clouds at 1500 ft. Therefore, I elected to fly direct oakland, then pao, to stay low. This was my first trip along this route. After passing oak, the tower controller told me to fly to the 'midspan of the san mateo bridge.' this bridge has a long part which is very low, and a high part, where ships pass under. I assumed that the 'midspan' was the high part, flanked on both sides by lower parts of the bridge. Once I could see the bridge in the haze I flew towards the high part, thinking this was the 'midspan' I should head towards. However, this high part is in the class B airspace of sfo. Fortunately, the 'extremely helpful!' oak tower controller caught me heading towards the class B boundary and gave me a 20 degree vector to the left to avoid class B airspace. The direct cause for nearly entering class B was not knowing the local terminology: 'midspan' refers literally to the middle of a bridge, not the distinct part where it is high above the water.

Original NASA ASRS Text

Title: C150 PLT MISINTERPS CTLR'S VISUAL NAV REF.

Narrative: I FLEW MY C150H FROM SONOMA SKYPARK (0Q9) TO PALO ALTO (PAO), CA. THE WX WAS VERY HAZY, WITH SOME CLOUDS AT 1500 FT. THEREFORE, I ELECTED TO FLY DIRECT OAKLAND, THEN PAO, TO STAY LOW. THIS WAS MY FIRST TRIP ALONG THIS RTE. AFTER PASSING OAK, THE TWR CTLR TOLD ME TO FLY TO THE 'MIDSPAN OF THE SAN MATEO BRIDGE.' THIS BRIDGE HAS A LONG PART WHICH IS VERY LOW, AND A HIGH PART, WHERE SHIPS PASS UNDER. I ASSUMED THAT THE 'MIDSPAN' WAS THE HIGH PART, FLANKED ON BOTH SIDES BY LOWER PARTS OF THE BRIDGE. ONCE I COULD SEE THE BRIDGE IN THE HAZE I FLEW TOWARDS THE HIGH PART, THINKING THIS WAS THE 'MIDSPAN' I SHOULD HEAD TOWARDS. HOWEVER, THIS HIGH PART IS IN THE CLASS B AIRSPACE OF SFO. FORTUNATELY, THE 'EXTREMELY HELPFUL!' OAK TWR CTLR CAUGHT ME HEADING TOWARDS THE CLASS B BOUNDARY AND GAVE ME A 20 DEG VECTOR TO THE L TO AVOID CLASS B AIRSPACE. THE DIRECT CAUSE FOR NEARLY ENTERING CLASS B WAS NOT KNOWING THE LCL TERMINOLOGY: 'MIDSPAN' REFERS LITERALLY TO THE MIDDLE OF A BRIDGE, NOT THE DISTINCT PART WHERE IT IS HIGH ABOVE THE WATER.

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.