Narrative:

I was flying VFR in VMC during the daytime along the beach; having departed about 10 minutes prior from ZZZ. I was monitoring approach and guard on 121.5 during this phase of flight but had not called in to request VFR flight following as I normally do. As I was flying along the coast; I planned an altitude of 3;000 feet MSL/AGL; so I could obtain proper engine performance without having to fly required VFR altitudes above 3;000 feet AGL per part 91.159 (which would reduce required engine performance for this flight). I was using the current altimeter setting as broadcast by the ZZZ AWOS; 30.14. As I climbed to 3;000 feet just prior to crossing the harbor; I noticed a B737 about two to three miles ahead of me at or near my altitude flying perpendicular to my route (it was heading towards the ocean). The B737 then began a sharp left turn towards my position; which put its path almost directly in conflict with my aircraft. As the B737 turned toward me; it then made a steep pitch up in what appeared to be an effort to climb in order to maintain separation from my aircraft. Our paths crossed with the B737 passing above and just behind my aircraft at what I would guess to be 800-1000 feet vertical distance and possibly lesser horizontal distance. I maintained visual contact with the B737; noticed its [company] livery; and prepared to make a quick turn and descent away from it to avoid it; though evasive action on my part was unnecessary due to the B737's climb and turn. Still; I was surprised that a controlled commercial aircraft on approach to ZZZ1 would be permitted to get this close to my aircraft. My aircraft is equipped with 1090 es ads-B out; so my altitude and position were being transmitted to ATC. I confirmed this by running an FAA papr report for this particular flight; which showed no in-flight transmission error.because I did not hear any transmissions on the radio between B737 and approach; I pulled up the ATC recording later that evening and also looked at its flight track on flight aware once I learned the call sign. On the tape; I heard the controller instructing B737 to descend and maintain 3;000 feet. A few minutes later the controller instructed B737 to turn left to 120 degrees. The controller then advised the B737 to maintain 3;000 feet and advised it of a VFR aircraft at 7 o'clock; type unknown; 3 miles away at 2;100 feet. B737 replied; 'looking.' a minute or so later; ATC instructed B737 to turn to 330 degrees. Then shortly after ATC instructed it to continue a left turn to 300. B737 acknowledged the instruction; then ATC ordered it to turn immediately due to traffic at 1 o'clock and 2 miles at 3;000 feet (presumably my aircraft). B737 responded 'looking.' the controller did not instruct B737 to climb; but according to its flight track on flight aware the aircraft made a +1250/min climb at this point in time; which corresponds with the steep pitch angle I noticed when it neared my aircraft. ATC then instructed B737 to continue direct to ZZZ1 (presumably after our aircraft passed each other). Prior to initiating its climb; aircraft Y was indicating approximately 2;800 feet per flight aware so there may have been a deviation from its assigned altitude; though this may have been its uncorrected pressure altitude.while it is entirely possible that no separation minima were violated in this instance; I feel there are a few lessons to be learned. First; even though I had just departed an uncontrolled field 10 minutes prior; it is important for me to request VFR flight following when flying towards a relatively busy approach path so I can be routed around conflicting traffic. Second; I feel that earlier action by either the controller or the B737 pilots (if they were equipped with TCAS) would have allowed better separation; since my steady heading and altitude were being broadcast to the controller. Third; this instance has motivated me to equip my aircraft with ads-B in so I can have advance warning of otheraircraft near me and take corrective advance to avoid situations like this one.

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Original NASA ASRS Text

Title: Piper 32 pilot reported an NMAC with a B737 aircraft.

Narrative: I was flying VFR in VMC during the daytime along the beach; having departed about 10 minutes prior from ZZZ. I was monitoring Approach and guard on 121.5 during this phase of flight but had not called in to request VFR flight following as I normally do. As I was flying along the coast; I planned an altitude of 3;000 feet MSL/AGL; so I could obtain proper engine performance without having to fly required VFR altitudes above 3;000 feet AGL per Part 91.159 (which would reduce required engine performance for this flight). I was using the current altimeter setting as broadcast by the ZZZ AWOS; 30.14. As I climbed to 3;000 feet just prior to crossing the harbor; I noticed a B737 about two to three miles ahead of me at or near my altitude flying perpendicular to my route (it was heading towards the ocean). The B737 then began a sharp left turn towards my position; which put its path almost directly in conflict with my aircraft. As the B737 turned toward me; it then made a steep pitch up in what appeared to be an effort to climb in order to maintain separation from my aircraft. Our paths crossed with the B737 passing above and just behind my aircraft at what I would guess to be 800-1000 feet vertical distance and possibly lesser horizontal distance. I maintained visual contact with the B737; noticed its [company] livery; and prepared to make a quick turn and descent away from it to avoid it; though evasive action on my part was unnecessary due to the B737's climb and turn. Still; I was surprised that a controlled commercial aircraft on approach to ZZZ1 would be permitted to get this close to my aircraft. My aircraft is equipped with 1090 ES ADS-B out; so my altitude and position were being transmitted to ATC. I confirmed this by running an FAA PAPR report for this particular flight; which showed no in-flight transmission error.Because I did not hear any transmissions on the radio between B737 and Approach; I pulled up the ATC recording later that evening and also looked at its flight track on Flight Aware once I learned the call sign. On the tape; I heard the Controller instructing B737 to descend and maintain 3;000 feet. A few minutes later the controller instructed B737 to turn left to 120 degrees. The Controller then advised the B737 to maintain 3;000 feet and advised it of a VFR aircraft at 7 o'clock; type unknown; 3 miles away at 2;100 feet. B737 replied; 'looking.' A minute or so later; ATC instructed B737 to turn to 330 degrees. Then shortly after ATC instructed it to continue a left turn to 300. B737 acknowledged the instruction; then ATC ordered it to turn immediately due to traffic at 1 o'clock and 2 miles at 3;000 feet (presumably my aircraft). B737 responded 'looking.' The controller did not instruct B737 to climb; but according to its flight track on Flight Aware the aircraft made a +1250/min climb at this point in time; which corresponds with the steep pitch angle I noticed when it neared my aircraft. ATC then instructed B737 to continue direct to ZZZ1 (presumably after our aircraft passed each other). Prior to initiating its climb; Aircraft Y was indicating approximately 2;800 feet per Flight Aware so there may have been a deviation from its assigned altitude; though this may have been its uncorrected pressure altitude.While it is entirely possible that no separation minima were violated in this instance; I feel there are a few lessons to be learned. First; even though I had just departed an uncontrolled field 10 minutes prior; it is important for me to request VFR flight following when flying towards a relatively busy approach path so I can be routed around conflicting traffic. Second; I feel that earlier action by either the controller or the B737 pilots (if they were equipped with TCAS) would have allowed better separation; since my steady heading and altitude were being broadcast to the controller. Third; this instance has motivated me to equip my aircraft with ADS-B in so I can have advance warning of otheraircraft near me and take corrective advance to avoid situations like this one.

Data retrieved from NASA's ASRS site 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.