Narrative:

About ten-miles from ZZZ; we were cleared to descend to 1600' and cleared for the ILS xx. Weather was day; cavu (clear visibility unlimited); and we were at about 3000'; flaps 5; landing gear down; and about 175 knots. The autopilot caught the localizer and glideslope; and I disconnected the autopilot and autothrottle at about 3000'. At about 2500' on glideslope; the approach controller told us to expedite our descent for traffic at 1 to 2 o'clock. As I was hand flying; I asked for flaps 15; and began descent below the glideslope; and we could see the traffic on the horizon (appeared to be a high-wing; single-engine GA aircraft); and got a TA on TCAS. The aircraft showed 300' above us on TCAS. Shortly thereafter; we received a 'descend' RA. I increased my descent rate to comply with the guidance. I would guess I was doing about 1500 fpm descent at about 175 knots. The GA aircraft passed directly over the ILS xx final; and directly over us by less than 1000'; and probably closer to 500'. We received 'clear of conflict' at about 1300'; leveled; configured; and complied with stabilized approach criteria by 1000' AGL; so we continued the approach and informed TRACON; who said they thought ZZZ tower was trying to get him to stop his descent. I don't believe passengers were aware of the incident.airspace that provides more protection to IFR aircraft on a published instrument approach going into ZZZ. We should not be getting descend ras below 2;000' while on (or actually below) glideslope on approach into a towered airport. (Unless; of course; the GA aircraft was at fault and not compliant with regulations. Then the preventative measure would be corrective action against the pilot.)

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Original NASA ASRS Text

Title: B737 flight crew reported a near miss with a GA Aircraft on final.

Narrative: About ten-miles from ZZZ; we were cleared to descend to 1600' and cleared for the ILS XX. Weather was Day; CAVU (Clear Visibility Unlimited); and we were at about 3000'; flaps 5; landing gear down; and about 175 knots. The autopilot caught the localizer and glideslope; and I disconnected the autopilot and autothrottle at about 3000'. At about 2500' on glideslope; the Approach Controller told us to expedite our descent for traffic at 1 to 2 o'clock. As I was hand flying; I asked for flaps 15; and began descent below the glideslope; and we could see the traffic on the horizon (appeared to be a high-wing; single-engine GA aircraft); and got a TA on TCAS. The aircraft showed 300' above us on TCAS. Shortly thereafter; we received a 'DESCEND' RA. I increased my descent rate to comply with the guidance. I would guess I was doing about 1500 fpm descent at about 175 knots. The GA aircraft passed directly over the ILS XX final; and directly over us by less than 1000'; and probably closer to 500'. We received 'clear of conflict' at about 1300'; leveled; configured; and complied with stabilized approach criteria by 1000' AGL; so we continued the approach and informed TRACON; who said they thought ZZZ Tower was trying to get him to stop his descent. I don't believe Passengers were aware of the incident.Airspace that provides more protection to IFR aircraft on a published instrument approach going into ZZZ. We should not be getting DESCEND RAs below 2;000' while on (or actually below) glideslope on approach into a towered airport. (unless; of course; the GA aircraft was at fault and not compliant with regulations. Then the preventative measure would be corrective action against the pilot.)

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.