GA pilot and local controller reported an NMAC occurred when the pilot lost sight of another aircraft while maneuvering in the traffic pattern at night.
Synopsis
GA pilot and local controller reported an NMAC occurred when the pilot lost sight of another aircraft while maneuvering in the traffic pattern at night.
Narrative
We were coming in to ZZZ; cleared to land [Runway] XXR and on around a 3 mile approximated right base at 2500 MSL. A Comanche had just been cleared for a right southeast turn departure. We were told by tower that the Comanche was turning and asked if we saw the traffic. I saw the landing light turn right at us and saw on foreflight TCAS that they were 1000 feet below us at 1500 ft MSL. We told tower we had the traffic. About 30 seconds later; they turned off their landing light and we lost them. Continued looking for them again while continuing our right base and on TCAS they were now 500 feet below us climbing and headed straight towards us. We told tower that we lost sight of them; and tower said they are half a mile to your right. This was when we started to prepare for an evasion. We knew by the rules we should make a right hand turn; but if we had done that we would have turned right into them and had a head on collision. We finally saw them seconds later; they were directly to the right of our nose; they saw us the same time and evaded to the right on a steep turn and decent; we evaded to the left as to not turn into them. We were same altitude very close to each other and never heard the Comanche on the frequency after his departure turn toward us. We saw the entire belly of their plane in front of us. After we avoided them with the left turn we asked tower for vectors to final as we lost situational awareness at night due to the evasion.
Second reporter narrative
A C150 called inbound from the East; told to enter a right base for Runway XXR. A PA24 issued a right turn out and cleared for take off from Runway XXR. As PA24 started his turn and climb on course and both aircraft were approximately 5 mi apart; I issued traffic to both aircraft. C150 said they had the PA24 in sight; I acknowledged that and cleared them to land. I told the PA24 to keep an eye out for the other aircraft as they departed but that the other aircraft did have them in sight and to contact departure. A few minutes later the C150 said they 'lost the other aircraft and asked where he was'. At that point I issued traffic again and the PA24 was passing off their right side at less than 1/2 mi. In hindsight; I could have asked the Cessna again if they *still* had the airplane in sight that they said they had in sight when they were two miles apart. I also could have kept both aircraft until they passed and turned the departure or turned the arrival which all seemed unnecessary at the time because the arrival said they had the other aircraft in sight. I guess the moral of the story for me is don't trust pilots and ensure that they're doing what they say they're ding.
Source: NASA Aviation Safety Reporting System (public domain). Reports are voluntary submissions and are not verified by NASA.