Narrative:

During our visual approach to runway 30L into sjc; we were advised at approximately 7 mile final of traffic 1 mile ahead altitude and type unknown and tower was not talking to them. We both scanned visually for traffic and also looked at the TCAS display. Neither of us saw traffic nor was there any indication of traffic on TCAS as we continued our visual approach. At approximately 500 feet AGL; tower ordered us to go-around; that there was additional traffic on short final that wasn't talking to him. First officer (first officer)/ pilot flying (PF) initiated the go-around and I responded to tower that we were going around and that we didn't see anybody or have anybody on our TCAS. He said there was a plane on short final he wasn't talking to and he could see them. We executed the go around normally; ran all appropriate check lists; advised the flight attendants (flight attendant) and passengers and set up for another visual approach to runway 30L. The approach and landing continued without incident.as we taxied to the gate; I asked the controller if he ever got ahold of the other aircraft; and he said they were on the phone with her now and he offered a phone number to call in case I wanted more information. I called the tower and he told me that basically they received a call from an FBO on the field advising they received a phone call from a [small aircraft] with an electrical emergency and they were inbound to the airport. Tower then called the pilot's cell phone and the pilot advised them they were on short final for 30L. This was at the same time we were on short final for 30L. It was then that he told me that in fact he didn't see the other aircraft; but they decided to send us around anyways. Being at night; with the other aircraft having no lights or transponder they could have been in front of us; behind us; above us or below us. We never saw them; and the tower didn't either. This could have been a very tragic incident had they been above us when we executed the go-around. The other aircraft neglected to follow procedures to enter the traffic pattern without first establishing contact with the tower and using light gun signals.

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Original NASA ASRS Text

Title: Small NORDO aircraft at night caused a go around for an inbound flight at a major airport.

Narrative: During our visual approach to runway 30L into SJC; we were advised at approximately 7 mile final of traffic 1 mile ahead altitude and type unknown and tower was not talking to them. We both scanned visually for traffic and also looked at the TCAS display. Neither of us saw traffic nor was there any indication of traffic on TCAS as we continued our visual approach. At approximately 500 feet AGL; tower ordered us to go-around; that there was additional traffic on short final that wasn't talking to him. First Officer (FO)/ Pilot Flying (PF) initiated the go-around and I responded to tower that we were going around and that we didn't see anybody or have anybody on our TCAS. He said there was a plane on short final he wasn't talking to and he could see them. We executed the go around normally; ran all appropriate check lists; advised the Flight Attendants (FA) and passengers and set up for another visual approach to runway 30L. The approach and landing continued without incident.As we taxied to the gate; I asked the controller if he ever got ahold of the other aircraft; and he said they were on the phone with her now and he offered a phone number to call in case I wanted more information. I called the tower and he told me that basically they received a call from an FBO on the field advising they received a phone call from a [small aircraft] with an electrical emergency and they were inbound to the airport. Tower then called the pilot's cell phone and the pilot advised them they were on short final for 30L. This was at the same time we were on short final for 30L. It was then that he told me that in fact he DIDN'T see the other aircraft; but they decided to send us around anyways. Being at night; with the other aircraft having no lights or transponder they could have been in front of us; behind us; above us or below us. We never saw them; and the tower didn't either. This could have been a very tragic incident had they been above us when we executed the go-around. The other aircraft neglected to follow procedures to enter the traffic pattern without first establishing contact with the tower and using light gun signals.

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.