Narrative:

At the above date and time, I (PNF) was flying with a student pilot on a northeast heading en route to sql at 2500 ft MSL. We were monitoring the sql tower frequency, but had not yet contacted them. Suddenly, I observed a piper aircraft at our 2 O'clock position and 1/4 mi, at our altitude, proceeding west, right to left. Before I could take evasive action, the piper crossed in front of us and missed us by about 250 ft! The piper continued toward half moon bay airport. I switched to the haf unicom frequency and heard 'cherokee, report 5 mi west of haf.' I had him in sight and am certain that was the aircraft that passed me. He gave no indication, by voice or aircraft path, that he ever saw us. The piper appeared to have at least 2 people on board, and the voice I heard was that of a male. Frankly, I don't know why I or my student didn't see the piper approaching sooner than we did. We were looking for other aircraft and not distraction by running a checklist, talking on the radio, etc. Further, we were in severe clear conditions. I will have to increase my vigilance in looking for other aircraft and teach my students to also do so.

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Original NASA ASRS Text

Title: NMAC BTWN A C172 TRAINING FLT IN LEVEL FLT AT 2500 FT UNDERNEATH CLASS B AIRSPACE AND A PIPER CHEROKEE IN LEVEL FLT XING IN FRONT OF THE C172. PLTS IN THE C172 DID NOT HAVE TIME TO REACT AND TAKE EVASIVE ACTION.

Narrative: AT THE ABOVE DATE AND TIME, I (PNF) WAS FLYING WITH A STUDENT PLT ON A NE HDG ENRTE TO SQL AT 2500 FT MSL. WE WERE MONITORING THE SQL TWR FREQ, BUT HAD NOT YET CONTACTED THEM. SUDDENLY, I OBSERVED A PIPER ACFT AT OUR 2 O'CLOCK POS AND 1/4 MI, AT OUR ALT, PROCEEDING W, R TO L. BEFORE I COULD TAKE EVASIVE ACTION, THE PIPER CROSSED IN FRONT OF US AND MISSED US BY ABOUT 250 FT! THE PIPER CONTINUED TOWARD HALF MOON BAY ARPT. I SWITCHED TO THE HAF UNICOM FREQ AND HEARD 'CHEROKEE, RPT 5 MI W OF HAF.' I HAD HIM IN SIGHT AND AM CERTAIN THAT WAS THE ACFT THAT PASSED ME. HE GAVE NO INDICATION, BY VOICE OR ACFT PATH, THAT HE EVER SAW US. THE PIPER APPEARED TO HAVE AT LEAST 2 PEOPLE ON BOARD, AND THE VOICE I HEARD WAS THAT OF A MALE. FRANKLY, I DON'T KNOW WHY I OR MY STUDENT DIDN'T SEE THE PIPER APCHING SOONER THAN WE DID. WE WERE LOOKING FOR OTHER ACFT AND NOT DISTR BY RUNNING A CHKLIST, TALKING ON THE RADIO, ETC. FURTHER, WE WERE IN SEVERE CLR CONDITIONS. I WILL HAVE TO INCREASE MY VIGILANCE IN LOOKING FOR OTHER ACFT AND TEACH MY STUDENTS TO ALSO DO SO.

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.