Date: 201606
Local time of day: 1201-1800
Location: BED.Tower, MA
Flight conditions: VMC
Light: Daylight
Aircraft: Small Aircraft; High Wing; 1 Eng; Fixed Gear
Operator: FBO
Operating under: Part 91
Flight plan: VFR
Mission: Personal
Flight phase: Final Approach
Airspace: Class D BED
ATC / advisory: Tower BED
Second aircraft: Helicopter
Reporter organization: Government
Reporter function: Local; Instructor
Reporter qualification: Air Traffic Control Fully Certified
Human factors: Training / Qualification; Workload; Situational Awareness; Communication Breakdown; Distraction
Second reporter function: Trainee; Local
Anomaly: ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Returned To Clearance; Flight Crew Took Evasive Action
Contributing factors: Procedure; Human Factors
Primary problem: Procedure

Narrative: I was training a developmental that had 140 plus hours on local control. RWY 23 was active and Aircraft X was in the right downwind. Aircraft Y was on the right base to RWY 23. Aircraft X was instructed to make a left 360 when they were midfield. As they were rolling out of the 360 I pointed the aircraft out to the developmental. She instructed them to make another tight left 360 and they acknowledged. We did not tell Aircraft Y about Aircraft X in a 360 abeam the numbers. We did tell Aircraft X about Aircraft Y and they would be number 3 to follow. I told the trainee traffic for one is traffic for another but we never called it on frequency.We had an aircraft on short final so I scanned gear and the RWY. A helicopter was operating on the east side of the airspace. They called up to tell us they were tracking RT3 northbound and they were going to be hovering on about a 3 mile final for RWY23. As I scanned back to the northwest; Aircraft Y keyed up and said they had traffic directly ahead and inquired what they were doing. They also said they took evasive maneuvers to avoid. At this point I keyed up let Aircraft Y know the traffic was now behind them and they were cleared to land. I told Aircraft X they were #2 and cleared to land. I saw out the window what was happening but the helicopter was still talking blocking the frequency. Aircraft X flew at least another mile in the downwind from when being instructed to make a 360 and when they started it. Aircraft X complied with the first 360 appropriately.The ATM and two people for an ECV audit were upstairs. Additionally; the CIC/GC/FD positions were combined and there was a position relief briefing in progress. A90 had called twice over the shout line to coordinate an arrival to RWY29 at the same time. Change my scanning techniques. I saw Aircraft X abeam the numbers and they went to the rwy. The helicopter called so I looked and scanned their flight path before going back to Aircrafts X and Y. I could've reached out on guard to see if either aircraft were monitoring.


Second narrative: [Report narrative contained no additional information.]


Synopsis: BED Tower controllers reported an aircraft was supposed to make a 360 on downwind; but did not and caused a conflict with a helicopter.