B737 captain reported being vectored off the approach to avoid a light twin pilot that could not or ...

Narrative:

I am writing this report because of a safety concern; there were no mistakes or concerns with our flight just a light twin that was trying to fly the rnp approach and could not complete it or follow ATC instructions.we were about to start the approach when we heard approach control trying to get the light twin to stay on assigned heading and climb. Over and over he had to tell him; you are turning the wrong way; you are not climbing. He cleared us for approach and I got a visual on him of my left wing; again ATC was trying to get him on heading and altitude. I was getting concerned about being close to the guy and asked ATC to keep us away from him; a short time after that we were told to make a right turn off the approach and climb to 4000'. He then told the guy; just fly straight. He asked him to go to a VFR field; land and get it together and try the approach later. The guy said no; he was then told he couldn't do the rnp again and tried the localizer next.we were back on the approach at that point and had an uneventful landing. I would like to add that the approach controller did a great job dealing with the other pilot.my concern is having light twins flown by pilots that shouldn't be flying IFR (due to lack of experience) being in the same place that we are flying. The result is that it makes for a tense and stressful situation. Again I am only writing this to point out a safety concern.

Original NASA ASRS Text

Title: B737 Captain reported being vectored off the approach to avoid a light twin pilot that could not or would not comply with ATC instruction.

Narrative: I am writing this report because of a safety concern; there were no mistakes or concerns with our flight just a light twin that was trying to fly the RNP Approach and could not complete it or follow ATC instructions.We were about to start the approach when we heard Approach Control trying to get the light twin to stay on assigned heading and climb. Over and over he had to tell him; you are turning the wrong way; you are not climbing. He cleared us for approach and I got a visual on him of my left wing; again ATC was trying to get him on heading and altitude. I was getting concerned about being close to the guy and asked ATC to keep us away from him; a short time after that we were told to make a right turn off the approach and climb to 4000'. He then told the guy; just fly straight. He asked him to go to a VFR field; land and get it together and try the approach later. The guy said no; he was then told he couldn't do the RNP again and tried the LOC next.We were back on the approach at that point and had an uneventful landing. I would like to add that the Approach Controller did a great job dealing with the other Pilot.My concern is having light twins flown by Pilots that shouldn't be flying IFR (due to lack of experience) being in the same place that we are flying. The result is that it makes for a tense and stressful situation. Again I am only writing this to point out a safety concern.

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.

Attributes
ACN	1477158
Time
Date	201708
Local Time Of Day	1201-1800
Place
Locale Reference	SCT.TRACON
State Reference	CA
Environment
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Initial Approach
Flight Plan	IFR
Aircraft 2
Make Model Name	Small Aircraft Low Wing 2 Eng Retractable Gear
Flight Phase	Initial Approach
Person 1
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	No Specific Anomaly Occurred All Types

B737 captain reported being vectored off the approach to avoid a light twin pilot that could not or would not comply with ATC instruction.