Narrative:

I was plting a C150 on a short VFR flight from sdl to chd in the east phoenix metropolitan area, underneath the phoenix class B airspace. This flight was conducted in day VFR conditions, and I had a single passenger on board at the time. Northwest of ffz, and outside their class D airspace, I had a close encounter with other traffic that created a safety of flight issue. At the time of the incident, I had called ffz tower approximately 8 mi northwest at 2700 ft to advise them that I would be passing sbound just outside their class D airspace en route to chd. This transition would occur under the 3000 ft floor of the phx class B airspace, thus I was not in contact with phx approach at the time. The tower controller on duty approved my transition request at or above 2700 ft, and then advised me of eastbound type-unknown traffic at the same altitude. I advised that I observed the eastbound traffic, and I estimated this traffic at around 3 mi distant. The aircraft type appeared to be a single-engine cessna, thus I assumed his airspeed to be comparable to mine. At the time of observation, I expected to pass in front of this traffic at least 1 mi in front of him, and thus estimated him not to be a conflict factor. At that time, the opposing traffic also called ffz tower, and idented himself as an eastbound-transitioning cessna caravan en route to iwa. He would have just emerged from the phx class B airspace's surface -- 10000 ft segment (ending at dobson road), and was probably just released from radar contact by phx approach. The caravan pilot also advised the ffz tower controller that he had me in sight. At this point, we were beginning to rapidly converge, and I was beginning to realize that the caravan was far faster than I had anticipated, and separation was a potential problem. However, I realized that I was presented with a set of restrs that made an avoidance maneuver decision difficult: quickly climbing to avoid the closing traffic would very possibly violate the phoenix class B 10000-3000 ft segment without clearance. Since the recent opening of the third runway at phx, their arrs often descend very close to this 3000 ft floor, so I didn't want to risk a climb. Turning right to avoid the traffic risked violating the 10000 ft, sfc part of the class B airspace. Also, I would have had to turn towards him, and I was not certain that the turn radius would be short enough to avoid head-on conflict. Ffz tower approved my transition at or above 2700 ft. A descent would have immediately violated this restr (although I technically was not in his class D airspace), and I was not certain that the space below would be clear for my use. I chose to proceed straight ahead and hope that the caravan pilot would pass behind me. He appeared to do this, and I would estimate that he passed behind me by approximately 1/2 mi and slightly above. The ffz tower controller once again asked me if I had the traffic in sight, and I advised that it was no longer a factor. In retrospect, I could have descended to avoid traffic contrary to ATC instructions per part 91.123. I did not do this because of uncertainty of possible traffic below. The airspace within which I've described this incident is often crowded, with little open maneuvering space for transitioning VFR traffic. Another option for this transition would have been to overfly ffz at 3500 ft. This is not a direct routing for the path I needed to fly, but would have allowed room for decision and action. One other option to study for preventing future incidents of this sort may be to publish some form of alternate transition altitudes for close corridors/intxns like this, such as east/west at 2500 ft, north/south at 2800 ft, and so forth.

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Original NASA ASRS Text

Title: A C150 AND A C208 IN VISUAL CONDITIONS TRANSITING THE CLASS E AIRSPACE NEAR THE COMPLICATED PHX CLASS B AIRSPACE AND ITS UNDERLYING CLASS D AIRSPACE BECOME TFC CONFLICT PROBS FOR EACH OTHER.

Narrative: I WAS PLTING A C150 ON A SHORT VFR FLT FROM SDL TO CHD IN THE E PHOENIX METROPOLITAN AREA, UNDERNEATH THE PHOENIX CLASS B AIRSPACE. THIS FLT WAS CONDUCTED IN DAY VFR CONDITIONS, AND I HAD A SINGLE PAX ON BOARD AT THE TIME. NW OF FFZ, AND OUTSIDE THEIR CLASS D AIRSPACE, I HAD A CLOSE ENCOUNTER WITH OTHER TFC THAT CREATED A SAFETY OF FLT ISSUE. AT THE TIME OF THE INCIDENT, I HAD CALLED FFZ TWR APPROX 8 MI NW AT 2700 FT TO ADVISE THEM THAT I WOULD BE PASSING SBOUND JUST OUTSIDE THEIR CLASS D AIRSPACE ENRTE TO CHD. THIS TRANSITION WOULD OCCUR UNDER THE 3000 FT FLOOR OF THE PHX CLASS B AIRSPACE, THUS I WAS NOT IN CONTACT WITH PHX APCH AT THE TIME. THE TWR CTLR ON DUTY APPROVED MY TRANSITION REQUEST AT OR ABOVE 2700 FT, AND THEN ADVISED ME OF EBOUND TYPE-UNKNOWN TFC AT THE SAME ALT. I ADVISED THAT I OBSERVED THE EBOUND TFC, AND I ESTIMATED THIS TFC AT AROUND 3 MI DISTANT. THE ACFT TYPE APPEARED TO BE A SINGLE-ENG CESSNA, THUS I ASSUMED HIS AIRSPD TO BE COMPARABLE TO MINE. AT THE TIME OF OBSERVATION, I EXPECTED TO PASS IN FRONT OF THIS TFC AT LEAST 1 MI IN FRONT OF HIM, AND THUS ESTIMATED HIM NOT TO BE A CONFLICT FACTOR. AT THAT TIME, THE OPPOSING TFC ALSO CALLED FFZ TWR, AND IDENTED HIMSELF AS AN EBOUND-TRANSITIONING CESSNA CARAVAN ENRTE TO IWA. HE WOULD HAVE JUST EMERGED FROM THE PHX CLASS B AIRSPACE'S SURFACE -- 10000 FT SEGMENT (ENDING AT DOBSON ROAD), AND WAS PROBABLY JUST RELEASED FROM RADAR CONTACT BY PHX APCH. THE CARAVAN PLT ALSO ADVISED THE FFZ TWR CTLR THAT HE HAD ME IN SIGHT. AT THIS POINT, WE WERE BEGINNING TO RAPIDLY CONVERGE, AND I WAS BEGINNING TO REALIZE THAT THE CARAVAN WAS FAR FASTER THAN I HAD ANTICIPATED, AND SEPARATION WAS A POTENTIAL PROB. HOWEVER, I REALIZED THAT I WAS PRESENTED WITH A SET OF RESTRS THAT MADE AN AVOIDANCE MANEUVER DECISION DIFFICULT: QUICKLY CLBING TO AVOID THE CLOSING TFC WOULD VERY POSSIBLY VIOLATE THE PHOENIX CLASS B 10000-3000 FT SEGMENT WITHOUT CLRNC. SINCE THE RECENT OPENING OF THE THIRD RWY AT PHX, THEIR ARRS OFTEN DSND VERY CLOSE TO THIS 3000 FT FLOOR, SO I DIDN'T WANT TO RISK A CLB. TURNING R TO AVOID THE TFC RISKED VIOLATING THE 10000 FT, SFC PART OF THE CLASS B AIRSPACE. ALSO, I WOULD HAVE HAD TO TURN TOWARDS HIM, AND I WAS NOT CERTAIN THAT THE TURN RADIUS WOULD BE SHORT ENOUGH TO AVOID HEAD-ON CONFLICT. FFZ TWR APPROVED MY TRANSITION AT OR ABOVE 2700 FT. A DSCNT WOULD HAVE IMMEDIATELY VIOLATED THIS RESTR (ALTHOUGH I TECHNICALLY WAS NOT IN HIS CLASS D AIRSPACE), AND I WAS NOT CERTAIN THAT THE SPACE BELOW WOULD BE CLR FOR MY USE. I CHOSE TO PROCEED STRAIGHT AHEAD AND HOPE THAT THE CARAVAN PLT WOULD PASS BEHIND ME. HE APPEARED TO DO THIS, AND I WOULD ESTIMATE THAT HE PASSED BEHIND ME BY APPROX 1/2 MI AND SLIGHTLY ABOVE. THE FFZ TWR CTLR ONCE AGAIN ASKED ME IF I HAD THE TFC IN SIGHT, AND I ADVISED THAT IT WAS NO LONGER A FACTOR. IN RETROSPECT, I COULD HAVE DSNDED TO AVOID TFC CONTRARY TO ATC INSTRUCTIONS PER PART 91.123. I DID NOT DO THIS BECAUSE OF UNCERTAINTY OF POSSIBLE TFC BELOW. THE AIRSPACE WITHIN WHICH I'VE DESCRIBED THIS INCIDENT IS OFTEN CROWDED, WITH LITTLE OPEN MANEUVERING SPACE FOR TRANSITIONING VFR TFC. ANOTHER OPTION FOR THIS TRANSITION WOULD HAVE BEEN TO OVERFLY FFZ AT 3500 FT. THIS IS NOT A DIRECT ROUTING FOR THE PATH I NEEDED TO FLY, BUT WOULD HAVE ALLOWED ROOM FOR DECISION AND ACTION. ONE OTHER OPTION TO STUDY FOR PREVENTING FUTURE INCIDENTS OF THIS SORT MAY BE TO PUBLISH SOME FORM OF ALTERNATE TRANSITION ALTS FOR CLOSE CORRIDORS/INTXNS LIKE THIS, SUCH AS E/W AT 2500 FT, N/S AT 2800 FT, AND SO FORTH.

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.