Commercial Fixed Wing
Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument
Situational Awareness; Communication Breakdown
Conflict Ground Conflict; Critical; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Flight Crew Executed Go Around / Missed Approach; Flight Crew Took Evasive Action
Human Factors
We were on a night ILS 13 approach at MDT with the FO as pilot flying. He has less than 200 hours Part 121 jet time logged. Weather was misty and Approach had abandoned Visual approaches and begun conducting ILS approaches while we were on their frequency because people weren't picking out the field in time. Around 1;500 AGL; I completed the Landing Checklist and we had already been cleared to land. I started looking outside again. I noticed what looked like strobe lights on the runway and said 'Is that a plane on the runway? The FO said 'No; just the runway lights.' I kept looking and it seemed to be slowly moving relative so I said; 'No; I'm pretty sure there's an airplane there. Are they departing someone?' We had not noted any other radio calls but ours since switching to Tower frequency. Transmitting; I said to Tower; 'Is there an airplane on the runway?' Harrisburg Tower called out to a Aircraft Y [small aircraft] 'no delay; turn left on Taxiway D!'About now; we passed through 500 feet and I made the normal call out but it did not seem like this other airplane was going to clear the runway in time. I do not know at what altitude but lower than I should have I called for my FO to go-around and we did. I reported Go-Around to Tower and he was still trying to talk to Aircraft Y so we just climbed runway heading. Only at about 1;800 feet did Tower tell us to climb to 3;000; turn left 040 and contact departure. We did and returned for a normal landing.Aircraft Y was lost and never turned off the runway. We do not know how long they were there. Tower did not notice it and cleared us to land on an occupied runway. If Tower saw as we thought we saw that Aircraft Y would not clear in time they could have canceled our landing clearance and ordered Go-Around but they did not. We were the last line of defense and broke the chain that could have led to an accident by being alert and not landing.
I was pilot flying. We were cleared to land by Tower. At approximately 1;000 feet AGL the Captain saw the lights of Aircraft Y (small aircraft) flashing on the approach end of the runway. The aircraft was stationary. He queried the tower who immediately told the Aircraft Y to expedite off the runway. Aircraft Y started to slowly roll forward; and as we descended to approximately 500 feet and both realized that there was no way the aircraft would clear the runway in time the Captain called for a go-around. We announced to tower what we were doing and executed the go-around procedure. At approximately 2;500 feet Tower assigned us a heading and altitude; switched us to departure; and we came around for a second ILS and landed. Private pilot at MDT failed to clear the runway; despite him landing minutes before us. Tower cleared us to land while he was still stationary on the runway.
Air carrier flight crew reported a small aircraft was still at the end of the runway during their final approach to MDT.  The flight crew decided to execute a go-around at 500 feet AGL.