SNA Tower controllers reported that a general aviation aircraft overshot the centerline of the parallel runway; creating a conflict with an air carrier aircraft who took evasive action to avoid a possible collision.

Report 1 | Narrative: I was working Aircraft X on final. I had previously handed off Aircraft Y who was inbound from the west for pattern work to the Local Control (LC2) controller. I had cleared him to land and told him about traffic on the downwind for the parallel runway. I told Aircraft X that traffic had him in sight and would maintain visual separation when Aircraft X was about 4 mile final and there was about 2 miles between him and Aircraft Y.

I had heard the controller working Aircraft Y tell Aircraft Y to maintain visual separation and caution wake turbulence which is how I knew that Aircraft Y reported Aircraft X in sight.I noticed that Aircraft Y was flying a shallower downwind than was usual and was doing about 120 kt. on the downwind which is considerable faster than what similar aircraft do on the downwind. I told the controller who was working Aircraft Y to 'watch for the slop over' because of the way Aircraft Y was flying. I then observed Aircraft Y turn base wide and 'slopped over' or veer into the path of Aircraft X.

I could not tell who was in front or behind from my perspective; but I then saw Aircraft X turn sharply to the right as if he was afraid that Aircraft Y was going to impact his left side. I then told the controller that Aircraft Y was too close to Aircraft X. The controller then proceeded to instruct Aircraft Y to start a climb and go around. Aircraft X then said that Aircraft Y was way too close to which I just replied 'Roger.' About 30 seconds later Aircraft X said he was executing missed approach so I issued the standard missed approach instructions which is heading 195 and climb and maintain 3000.I would strongly recommend to suspend all flight training at SNA.

The runways at SNA are 500 ft. apart which is extremely close. We are depending on low time or student pilots to turn the base in such a manner as to avoid colliding with airlines and jet traffic inbound on Runway 20R. The AFD instructs pilots to do a 15-degree offset dog leg for base to final turn. That is a lot to ask a pilot who is training or who just got the license. It's a complicated maneuver to begin with but it is a vital necessity due to the proximity of the runways.I see it constantly where the pattern workers on Runway 20L will slop over and veer into the final for Runway 20R.

It happens constantly and no matter how many times we tell pilots not to do it or correct the pilots; it happens on a regular basis. Luckily when there has been slop over; either nobody is on final for Runway 20R or the inbound traffic is far enough in front or behind the pattern worker to take enough corrective action. It is my own personal belief that someday a small aircraft will slop over and collide with an airliner or business jet inbound on Runway 20R. In my mind; if flight training is allowed to continue; it's not a question of 'IF' but a question of 'WHEN' a catastrophe will occur.

Mixing commercial jet traffic and VFR pattern workers who are either learning or have low time at SNA is a recipe for disaster that will cost a lot of people their lives. There are a number of neighboring airports where the student pilots can go and do their flight training without putting the lives of airline passengers at risk; I believe that right to live of 200 plus passengers on an airliner supersedes the right of a student pilot to learn to fly at SNA.

Report 2 | Narrative: Aircraft Y; in the traffic pattern and on the downwind leg; reported Aircraft X in sight. Pilot stated that he would maintain visual separation from Aircraft X. Aircraft Y was then cleared for the option" on Runway 20L. Aircraft X was on short final; arriving Runway 20R; which is 500 ft. laterally separated from the parallel Runway 20L.Runway 20R is the air carrier and primary IFR runway here at SNA at 5;700x150 ft. Runway 20L is the primary traffic pattern / light GA runway here at SNA at 2;887x75.

Aircraft Y turned final to Runway 20L off the left wing of Aircraft X; but overshot the centerline of Runway 20L; flying too-wide of a turn; and nearly cutting off Aircraft X; who had to take an evasive turning maneuver to avoid an NMAC. Aircraft X executed a go-around. John Wayne Orange County Airport (SNA) is a very busy Class C airspace air carrier airport in Southern California. The airport handles about 11.5 million passengers per year; while handling a high volume of arrivals and departures daily between XA:00 and XQ:00. The airport has two parallel runways (see above); and is situated on a 500-acre plot of land.

The airport has a large terminal that has 22 regularly used airline gates. It also has a ramp just south of the terminal used for air cargo operations. The airport has 3 FBOs on the field with a very high volume of corporate and private jet traffic.Through the years; there have been several close calls between pattern working light GA aircraft and airliners. There have been many light GA airplane incidents that have been attributed to wake turbulence. In my years at SNA; I have witnessed several very close calls between airliners and small aircraft conducting flight training.

As a controller; and as one who worked this high volume of traffic daily; I am baffled by the pressing need by these local flight schools to conduct flight training here at a busy air carrier facility. It is not uncommon to have 6 or 7 low time student pilots in the traffic pattern; right next to arriving and departing large and heavy aircraft. The airspace and airfield is so limited in space that it is a requirement for departing GA aircraft off Runway 20L to conduct an immediate left 15-degree offset turn to avoid "drifting" into departing jets off Runway 20R. The margin for error here at SNA is virtually none.

Airline pilots and passengers should not be put in this dangerous situation day to day. It is a common occurrence here to see student pilots soloing for the first time; in close quarters with airliners.I rarely feel the need to file a report regarding anything that will hinder the flying public in any way; but I've seen enough here at SNA to prompt me to do something to look out for peoples' lives. I highly recommend that SNA suspend flight training indefinitely. VFR itinerate traffic; no problem. Furthermore; to increase safety here; I recommend that Runway 20L be permanently decommissioned and recommissioned as a taxiway.

Furthermore; I recommend that an EMAS be installed at the departure ends of Runway 20R and Runway 02L. I would also recommend that a displaced threshold be built at the approach end of Runway 20R in order to increase the length of takeoff rolls for larger aircraft. The current 5;700-foot runway; in my opinion; is not enough of a safety margin when the land space currently exits for a displaced threshold for departures."

Report 1 | Synopsis: SNA Tower controllers reported that a general aviation aircraft overshot the centerline of the parallel runway; creating a conflict with an air carrier aircraft who took evasive action to avoid a possible collision.