Narrative:

WX at myf was reporting approximately 2000 AGL ceiling (broken); with see and rnm reporting sct 3000 AGL. The significant differences in the WX at such close airports was; I believe; due to the coastal marine stratus layer and the cold front then passing through. The planned flight was from myf to F70 with route myf-see-vpslj-rnm-F70-hmt-F70. Marginal VMC existed at myf (ceiling) with VMC for the remainder of the route; and no flight plan was filed for the part 91 personal flight. I expected that I would have to depart at a lower than normal altitude until I was east of see; at which point I would be able to climb to a more comfortable altitude for the remainder of the flight. Normally; I would climb to 2500 MSL on an eastbound departure from myf to remain above see class D. As I departed runway 23 at myf; I made a turn to left downwind and climb out. I leveled at 2000 MSL to remain clear of clouds and began my eastbound departure. As I departed myf class D; I was told to 'remain clear of class B; clear to switch.' this is the standard 'clear to switch' call for all aircraft departing myf. I immediately switched frequencys to see tower and requested to transition the north side of the class B airspace for nkx until I reached vpslj; at which point I was to turn northwards toward rnm and climb to 3500 MSL. As I evaluated the clouds; I determined that I could safely climb to 2500 MSL (above see class D) and did so; although I also evaluated that conditions to the north were not as forecast; with lowering ceilings and rising terrain. I decided to cancel the flight and return to myf. Once east of the see class D; I turned south to join the mt helix approach for myf at 2500 MSL. I completed a normal approach to runway 23 at myf; with a go around on the first pass due to excessive float and a normal landing on the second pass. As I replayed the flight in my mind; I realized that my visual cues may have been off and that I may have inadvertently passed just inside the southern edge of the nkx class B (at the 1800 MSL floor; aircraft altitude of 2000 MSL). A review of my chart and my visual memory indicated that I remained clear. I was also in continuous contact with either myf or see tower; neither of which advised me that I had strayed into the class B. However; the fact that there is doubt in my mind is enough to prompt this submission. What did I do wrong: a) I launched into marginal VMC with the expectation that it would get better further east. B) in launching; I deviated from my normal route/altitude of flight to remain VFR without fully evaluation my plan. Although I did plan to call see to transition their airspace; I did not choose enough landmarks to carefully track my progress that close to the class B. C) once I made the decision to divert; I lost focus on my immediate ground track while planning my return ground track. The wind drift (pushing the aircraft northeast) and the natural left turning tendency of the aircraft may have pushed me into the class B while I was thinking too far ahead. What did I do right: a) stayed in contact with tower(south) while I was in the vicinity and properly obtained permission to transition see class D. B) made a good decision to cancel and return when the visual indicated that the WX was not as expected. How will I keep it from happening again: a) as a low time pilot; I had set a personal minimum of 2000 ft AGL for ceilings. Since this experience indicates that this is inadequate; especially in the san diego area with class B airspace; significant terrain; and numerous other aircraft; I have reset my personal minimum to 2500 AGL to provide a more comfortable margin. B) on the san diego terminal area chart; I have mapped several routes with more explicit visual and VOR/DME cues to maintain the aircraft clear of the class B coming in and out of myf.

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Original NASA ASRS Text

Title: A C172 PLT PLANNED AND FLEW A VFR FLT IN MARGINAL VFR CONDITIONS. HE MAY HAVE INTRUDED ON SAN CLASS B AIRSPACE.

Narrative: WX AT MYF WAS REPORTING APPROX 2000 AGL CEILING (BKN); WITH SEE AND RNM REPORTING SCT 3000 AGL. THE SIGNIFICANT DIFFERENCES IN THE WX AT SUCH CLOSE ARPTS WAS; I BELIEVE; DUE TO THE COASTAL MARINE STRATUS LAYER AND THE COLD FRONT THEN PASSING THROUGH. THE PLANNED FLT WAS FROM MYF TO F70 WITH ROUTE MYF-SEE-VPSLJ-RNM-F70-HMT-F70. MARGINAL VMC EXISTED AT MYF (CEILING) WITH VMC FOR THE REMAINDER OF THE ROUTE; AND NO FLT PLAN WAS FILED FOR THE PART 91 PERSONAL FLIGHT. I EXPECTED THAT I WOULD HAVE TO DEPART AT A LOWER THAN NORMAL ALT UNTIL I WAS EAST OF SEE; AT WHICH POINT I WOULD BE ABLE TO CLB TO A MORE COMFORTABLE ALT FOR THE REMAINDER OF THE FLT. NORMALLY; I WOULD CLB TO 2500 MSL ON AN EBOUND DEP FROM MYF TO REMAIN ABOVE SEE CLASS D. AS I DEPARTED RWY 23 AT MYF; I MADE A TURN TO L DOWNWIND AND CLBOUT. I LEVELED AT 2000 MSL TO REMAIN CLEAR OF CLOUDS AND BEGAN MY EBOUND DEPARTURE. AS I DEPARTED MYF CLASS D; I WAS TOLD TO 'REMAIN CLEAR OF CLASS B; CLEAR TO SWITCH.' THIS IS THE STANDARD 'CLEAR TO SWITCH' CALL FOR ALL ACFT DEPARTING MYF. I IMMEDIATELY SWITCHED FREQS TO SEE TOWER AND REQUESTED TO TRANSITION THE NORTH SIDE OF THE CLASS B AIRSPACE FOR NKX UNTIL I REACHED VPSLJ; AT WHICH POINT I WAS TO TURN NORTHWARDS TOWARD RNM AND CLB TO 3500 MSL. AS I EVALUATED THE CLOUDS; I DETERMINED THAT I COULD SAFELY CLB TO 2500 MSL (ABOVE SEE CLASS D) AND DID SO; ALTHOUGH I ALSO EVALUATED THAT CONDITIONS TO THE NORTH WERE NOT AS FORECAST; WITH LOWERING CEILINGS AND RISING TERRAIN. I DECIDED TO CANCEL THE FLT AND RETURN TO MYF. ONCE EAST OF THE SEE CLASS D; I TURNED SOUTH TO JOIN THE MT HELIX APCH FOR MYF AT 2500 MSL. I COMPLETED A NORMAL APCH TO RWY 23 AT MYF; WITH A GAR ON THE FIRST PASS DUE TO EXCESSIVE FLOAT AND A NORMAL LNDG ON THE SECOND PASS. AS I REPLAYED THE FLT IN MY MIND; I REALIZED THAT MY VISUAL CUES MAY HAVE BEEN OFF AND THAT I MAY HAVE INADVERTENTLY PASSED JUST INSIDE THE SOUTHERN EDGE OF THE NKX CLASS B (AT THE 1800 MSL FLOOR; ACFT ALT OF 2000 MSL). A REVIEW OF MY CHART AND MY VISUAL MEMORY INDICATED THAT I REMAINED CLEAR. I WAS ALSO IN CONTINUOUS CONTACT WITH EITHER MYF OR SEE TWR; NEITHER OF WHICH ADVISED ME THAT I HAD STRAYED INTO THE CLASS B. HOWEVER; THE FACT THAT THERE IS DOUBT IN MY MIND IS ENOUGH TO PROMPT THIS SUBMISSION. WHAT DID I DO WRONG: A) I LAUNCHED INTO MARGINAL VMC WITH THE EXPECTATION THAT IT WOULD GET BETTER FURTHER EAST. B) IN LAUNCHING; I DEVIATED FROM MY NORMAL ROUTE/ALT OF FLT TO REMAIN VFR WITHOUT FULLY EVALUATION MY PLAN. ALTHOUGH I DID PLAN TO CALL SEE TO TRANSITION THEIR AIRSPACE; I DID NOT CHOOSE ENOUGH LANDMARKS TO CAREFULLY TRACK MY PROGRESS THAT CLOSE TO THE CLASS B. C) ONCE I MADE THE DECISION TO DIVERT; I LOST FOCUS ON MY IMMEDIATE GROUND TRACK WHILE PLANNING MY RETURN GROUND TRACK. THE WIND DRIFT (PUSHING THE ACFT NE) AND THE NATURAL LEFT TURNING TENDENCY OF THE ACFT MAY HAVE PUSHED ME INTO THE CLASS B WHILE I WAS THINKING TOO FAR AHEAD. WHAT DID I DO RIGHT: A) STAYED IN CONTACT WITH TOWER(S) WHILE I WAS IN THE VICINITY AND PROPERLY OBTAINED PERMISSION TO TRANSITION SEE CLASS D. B) MADE A GOOD DECISION TO CANCEL AND RETURN WHEN THE VISUAL INDICATED THAT THE WX WAS NOT AS EXPECTED. HOW WILL I KEEP IT FROM HAPPENING AGAIN: A) AS A LOW TIME PLT; I HAD SET A PERSONAL MINIMUM OF 2000 FT AGL FOR CEILINGS. SINCE THIS EXPERIENCE INDICATES THAT THIS IS INADEQUATE; ESPECIALLY IN THE SAN DIEGO AREA WITH CLASS B AIRSPACE; SIGNIFICANT TERRAIN; AND NUMEROUS OTHER ACFT; I HAVE RESET MY PERSONAL MINIMUM TO 2500 AGL TO PROVIDE A MORE COMFORTABLE MARGIN. B) ON THE SAN DIEGO TERMINAL AREA CHART; I HAVE MAPPED SEVERAL ROUTES WITH MORE EXPLICIT VISUAL AND VOR/DME CUES TO MAINTAIN THE ACFT CLEAR OF THE CLASS B COMING IN AND OUT OF MYF.

Data retrieved from NASA's ASRS site as of January 2009 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.