Narrative:

We began the published ILS approach to runway 17 at jyo leesburg; beginning at the initial approach fix still. This was our final approach for the evening; as we had completed night currency; and 2 ILS approaches at ZZZ. As we intercepted the localizer at still; I noticed M-20 approaching still behind us; about 5 miles away; and 500 ft. Above us; on a heading of 210 degrees. We continued the approach; with the PIC under the hood; and I continued to monitor for traffic. I was monitoring CTAF for leesburg; and had announced our arrival at still; and announced that we were on a 9 mile final for 17 as we passed the jotup intersection. We intersected jotup at 2;300 ft. To avoid the dulles bravo airspace floor at 2;500 ft.; and then descended to 2;100 ft. To intersect the glide slope at danmo; intending to fly the rest of the approach. During the transition from jotup to danmo; M-20 intersected the localizer at still; and rapidly closed the distance behind us. I attempted to contact the other aircraft on CTAF but got no response. As we reached danmo; I realized evasive action was needed because we were being overtaken by M-20; and would likely be collided with if we remained on the approach. I instructed the PIC to break off the approach; descend to 1;500 ft.; and do a right 360 to avoid the closing aircraft. As we began the right 360; M-20 finally announced on CTAF that they were on the ILS to leesburg. I tried to contact them again; informing them that they had just blown by us on approach; but received no acknowledgment. We completed the turn and again intersected danmo; and heard M-20's 'clear of runway 17' call; observing them taxiing off of the runway. I again tried to raise them on CTAF and received no response. We landed; and spoke with the pilots of M-20; and they said they were on an IFR flight plan; and that the potomac approach controller handed them off to CTAF at still; and told them that there was another aircraft ahead of them that they weren't talking to. The pilots said they didn't see our aircraft in front of them; despite our strobes; landing; navigation; and beacon lights being on; but that they saw an aircraft pass left to right as they did their approach.I suspect they were handed off to CTAF when they arrived at still; but waited too long afterwards to tune in the correct frequency and make their traffic announcements. They didn't make their first radio call until they were at danmo; and assumed that there was no traffic ahead of them on the ILS; or in the pattern because it was night.while I find it hard to believe they couldn't see us; there is a marked increase in the number of lights around the airport at leesburg; so it is easier to loose aircraft lights in the background of the new store and stadium lights. I also believe based on the nonchalant attitude of both pilots when I described what had occurred that there was an element of complacency as well. I don't believe it is nearly enough to make one radio call on CTAF that you're on the ILS; not even give a distance; and then make no further calls until clearing the runway. I feel like contacting CTAF after the hand-off from potomac approach was an afterthought at best.with the tower closed; traffic separation is solely the responsibility of pilots; and without the onboard ads-B capability in my G1000; I would have had no way to determine that there was an aircraft at my six o'clock rapidly approaching on a collision course.

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Original NASA ASRS Text

Title: Small aircraft pilot reported experiencing a NMAC with an IFR aircraft during final approach after the Tower had closed.

Narrative: We began the published ILS approach to Runway 17 at JYO Leesburg; beginning at the initial approach fix STILL. This was our final approach for the evening; as we had completed night currency; and 2 ILS approaches at ZZZ. As we intercepted the localizer at STILL; I noticed M-20 approaching STILL behind us; about 5 miles away; and 500 ft. above us; on a heading of 210 degrees. We continued the approach; with the PIC under the hood; and I continued to monitor for traffic. I was monitoring CTAF for Leesburg; and had announced our arrival at STILL; and announced that we were on a 9 mile final for 17 as we passed the JOTUP Intersection. We intersected JOTUP at 2;300 ft. to avoid the Dulles Bravo airspace floor at 2;500 ft.; and then descended to 2;100 ft. to intersect the glide slope at DANMO; intending to fly the rest of the approach. During the transition from JOTUP to DANMO; M-20 intersected the localizer at STILL; and rapidly closed the distance behind us. I attempted to contact the other aircraft on CTAF but got no response. As we reached DANMO; I realized evasive action was needed because we were being overtaken by M-20; and would likely be collided with if we remained on the approach. I instructed the PIC to break off the approach; descend to 1;500 ft.; and do a right 360 to avoid the closing aircraft. As we began the right 360; M-20 finally announced on CTAF that they were on the ILS to Leesburg. I tried to contact them again; informing them that they had just blown by us on approach; but received no acknowledgment. We completed the turn and again intersected DANMO; and heard M-20's 'Clear of Runway 17' call; observing them taxiing off of the runway. I again tried to raise them on CTAF and received no response. We landed; and spoke with the pilots of M-20; and they said they were on an IFR flight plan; and that the Potomac Approach Controller handed them off to CTAF at STILL; and told them that there was another aircraft ahead of them that they weren't talking to. The pilots said they didn't see our aircraft in front of them; despite our strobes; landing; NAV; and beacon lights being on; but that they saw an aircraft pass left to right as they did their approach.I suspect they were handed off to CTAF when they arrived at STILL; but waited too long afterwards to tune in the correct frequency and make their traffic announcements. They didn't make their first radio call until they were at DANMO; and assumed that there was no traffic ahead of them on the ILS; or in the pattern because it was night.While I find it hard to believe they couldn't see us; there is a marked increase in the number of lights around the airport at Leesburg; so it is easier to loose aircraft lights in the background of the new store and Stadium lights. I also believe based on the nonchalant attitude of both pilots when I described what had occurred that there was an element of complacency as well. I don't believe it is nearly enough to make one radio call on CTAF that you're on the ILS; not even give a distance; and then make no further calls until clearing the runway. I feel like contacting CTAF after the hand-off from Potomac Approach was an afterthought at best.With the Tower closed; traffic separation is solely the responsibility of pilots; and without the onboard ADS-B capability in my G1000; I would have had no way to determine that there was an aircraft at my six o'clock rapidly approaching on a collision course.

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.