Narrative:

The flight was a return trip on a VFR flight plan from bfl to the home base, rhv. In order to avoid lightning and showers observed over san luis reservoir and the pacheco pass area, I decided to fly over mt hamilton to reach rhv even though this would result in a nonstandard approach to the air traffic area. After receiving the ATIS, I contacted rhv tower at 10.7 NM on a bearing of 60 degrees from the airport and an altitude of 3500' MSL. The tower advised me to squawk 5300 and to enter a right downwind pattern for runway 31R following 2 other aircraft, one in the pattern and the other 2 mi north of the field. I replied, 'looking for traffic,' started scanning for traffic primarily in the area north to northeast of the airport, slowed to 80 KTS with full flaps to make a slow steep descent and turned on the taxi light. The beacon, navigation lights and strobes were on for the duration of the flight. The approach path was basically perpendicular to the runway with a small deviation to the right to permit a smooth entry into downwind at midfield. The meteorological visibility was better than 30 mi, with a slight haze and many reflections from cars. At approximately 8 NM from the field, the tower advised me of negative radar contact and asked for the transponder to be recycled. I complied and advised the tower. I can't remember if I said, 'still no contact with traffic.' a little later the tower asked for a position report. The LORAN was indicating 5.3 NM and a bearing of 060 degrees from rhv. I reported, '5 east of airport.' from the initial position report, I estimated the other aircraft to be well on downwind and started concentrating the scan in that area. I had already observed the first aircraft landing. Then #1 radio, which had been noisy before, started getting excessive interference, so I switched to radio #2. Approaching the pattern entry point I started getting real concerned about not seeing the other aircraft and advised the tower, 'still no contact,' while rocking the wings for a better look all around. The tower replied that the traffic was midfield. I hesitated for a moment, thinking that maybe the tower had the 2 aircraft confused, because I was midfield. At this point my wife spotted the other aircraft off to our immediate right and I executed a descending left turn to avoid physical contact. Based on later observations of parked aircraft at the airport, I estimate that we cleared by less than 150'. The pilot of the other aircraft advised the tower of the close call and the tower replied that they never received our squawk. Both planes landed safely west/O any further incidents, in the sequence originally specified by the tower. Comments: my perception of the problem is that it arose because of a certain amount of complacency in a radar environment and over reliance on ATC. In an uncontrolled environment I would have never gotten close to the pattern west/O seeing the other traffic. The unexpected failure of the transponder did not immediately lead to significantly increased position reporting. The tower controllers did not sound concerned, and we assumed based on the initial position report that sep would not be a problem, especially since we were approaching slowly and descending with good forward and downward visibility. Even though the tower never said so, I assumed that the tower had us in visual contact. We did not get initially alarmed at our failure to spot the other traffic and ask for position updates while still a good distance from the airport traffic pattern. The other pilot probably assumed that we were behind him and did not spot us either. The tower apparently never established visual contact with us until after the close call. The use of a nonstandard approach created additional problems. For the pilots it resulted in a much greater required scanning area. For the tower it presented a nonmoving target because we were basically flying directly to the tower. A disturbing thought is the apparent inability of the radar system to detect primary targets. Maybe too much background clutter from the hills. The only way I can see to minimize these kinds of problems in the future is to emulate uncontrolled airport procedures whenever any aircraft in the vicinity is not in continuous radar contact.

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Original NASA ASRS Text

Title: NMAC ON ENTRY TO DOWNWIND.

Narrative: THE FLT WAS A RETURN TRIP ON A VFR FLT PLAN FROM BFL TO THE HOME BASE, RHV. IN ORDER TO AVOID LIGHTNING AND SHOWERS OBSERVED OVER SAN LUIS RESERVOIR AND THE PACHECO PASS AREA, I DECIDED TO FLY OVER MT HAMILTON TO REACH RHV EVEN THOUGH THIS WOULD RESULT IN A NONSTANDARD APCH TO THE ATA. AFTER RECEIVING THE ATIS, I CONTACTED RHV TWR AT 10.7 NM ON A BEARING OF 60 DEGS FROM THE ARPT AND AN ALT OF 3500' MSL. THE TWR ADVISED ME TO SQUAWK 5300 AND TO ENTER A RIGHT DOWNWIND PATTERN FOR RWY 31R FOLLOWING 2 OTHER ACFT, ONE IN THE PATTERN AND THE OTHER 2 MI N OF THE FIELD. I REPLIED, 'LOOKING FOR TFC,' STARTED SCANNING FOR TFC PRIMARILY IN THE AREA N TO NE OF THE ARPT, SLOWED TO 80 KTS WITH FULL FLAPS TO MAKE A SLOW STEEP DSCNT AND TURNED ON THE TAXI LIGHT. THE BEACON, NAV LIGHTS AND STROBES WERE ON FOR THE DURATION OF THE FLT. THE APCH PATH WAS BASICALLY PERPENDICULAR TO THE RWY WITH A SMALL DEVIATION TO THE RIGHT TO PERMIT A SMOOTH ENTRY INTO DOWNWIND AT MIDFIELD. THE METEOROLOGICAL VIS WAS BETTER THAN 30 MI, WITH A SLIGHT HAZE AND MANY REFLECTIONS FROM CARS. AT APPROX 8 NM FROM THE FIELD, THE TWR ADVISED ME OF NEGATIVE RADAR CONTACT AND ASKED FOR THE TRANSPONDER TO BE RECYCLED. I COMPLIED AND ADVISED THE TWR. I CAN'T REMEMBER IF I SAID, 'STILL NO CONTACT WITH TFC.' A LITTLE LATER THE TWR ASKED FOR A POS RPT. THE LORAN WAS INDICATING 5.3 NM AND A BEARING OF 060 DEGS FROM RHV. I RPTED, '5 E OF ARPT.' FROM THE INITIAL POS RPT, I ESTIMATED THE OTHER ACFT TO BE WELL ON DOWNWIND AND STARTED CONCENTRATING THE SCAN IN THAT AREA. I HAD ALREADY OBSERVED THE FIRST ACFT LNDG. THEN #1 RADIO, WHICH HAD BEEN NOISY BEFORE, STARTED GETTING EXCESSIVE INTERFERENCE, SO I SWITCHED TO RADIO #2. APCHING THE PATTERN ENTRY POINT I STARTED GETTING REAL CONCERNED ABOUT NOT SEEING THE OTHER ACFT AND ADVISED THE TWR, 'STILL NO CONTACT,' WHILE ROCKING THE WINGS FOR A BETTER LOOK ALL AROUND. THE TWR REPLIED THAT THE TFC WAS MIDFIELD. I HESITATED FOR A MOMENT, THINKING THAT MAYBE THE TWR HAD THE 2 ACFT CONFUSED, BECAUSE I WAS MIDFIELD. AT THIS POINT MY WIFE SPOTTED THE OTHER ACFT OFF TO OUR IMMEDIATE RIGHT AND I EXECUTED A DSNDING LEFT TURN TO AVOID PHYSICAL CONTACT. BASED ON LATER OBSERVATIONS OF PARKED ACFT AT THE ARPT, I ESTIMATE THAT WE CLRED BY LESS THAN 150'. THE PLT OF THE OTHER ACFT ADVISED THE TWR OF THE CLOSE CALL AND THE TWR REPLIED THAT THEY NEVER RECEIVED OUR SQUAWK. BOTH PLANES LANDED SAFELY W/O ANY FURTHER INCIDENTS, IN THE SEQUENCE ORIGINALLY SPECIFIED BY THE TWR. COMMENTS: MY PERCEPTION OF THE PROB IS THAT IT AROSE BECAUSE OF A CERTAIN AMOUNT OF COMPLACENCY IN A RADAR ENVIRONMENT AND OVER RELIANCE ON ATC. IN AN UNCTLED ENVIRONMENT I WOULD HAVE NEVER GOTTEN CLOSE TO THE PATTERN W/O SEEING THE OTHER TFC. THE UNEXPECTED FAILURE OF THE TRANSPONDER DID NOT IMMEDIATELY LEAD TO SIGNIFICANTLY INCREASED POS RPTING. THE TWR CTLRS DID NOT SOUND CONCERNED, AND WE ASSUMED BASED ON THE INITIAL POS RPT THAT SEP WOULD NOT BE A PROB, ESPECIALLY SINCE WE WERE APCHING SLOWLY AND DSNDING WITH GOOD FORWARD AND DOWNWARD VIS. EVEN THOUGH THE TWR NEVER SAID SO, I ASSUMED THAT THE TWR HAD US IN VISUAL CONTACT. WE DID NOT GET INITIALLY ALARMED AT OUR FAILURE TO SPOT THE OTHER TFC AND ASK FOR POS UPDATES WHILE STILL A GOOD DISTANCE FROM THE ARPT TFC PATTERN. THE OTHER PLT PROBABLY ASSUMED THAT WE WERE BEHIND HIM AND DID NOT SPOT US EITHER. THE TWR APPARENTLY NEVER ESTABLISHED VISUAL CONTACT WITH US UNTIL AFTER THE CLOSE CALL. THE USE OF A NONSTANDARD APCH CREATED ADDITIONAL PROBS. FOR THE PLTS IT RESULTED IN A MUCH GREATER REQUIRED SCANNING AREA. FOR THE TWR IT PRESENTED A NONMOVING TARGET BECAUSE WE WERE BASICALLY FLYING DIRECTLY TO THE TWR. A DISTURBING THOUGHT IS THE APPARENT INABILITY OF THE RADAR SYS TO DETECT PRIMARY TARGETS. MAYBE TOO MUCH BACKGROUND CLUTTER FROM THE HILLS. THE ONLY WAY I CAN SEE TO MINIMIZE THESE KINDS OF PROBS IN THE FUTURE IS TO EMULATE UNCTLED ARPT PROCS WHENEVER ANY ACFT IN THE VICINITY IS NOT IN CONTINUOUS RADAR CONTACT.

Data retrieved from NASA's ASRS site as of August 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.