Bed tower local controller and a flight instructor reported a descent below the published pattern al...

Attributes
ACN	1703444
Time
Date	201911
Local Time Of Day	1201-1800
Place
Locale Reference	BED.Tower
State Reference	MA
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Small Aircraft
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Route In Use	None
Flight Plan	VFR
Aircraft 2
Make Model Name	Helicopter
Operating Under FAR Part	Part 91
Flight Phase	Final Approach
Flight Plan	VFR
Person 2
Function	Pilot Not Flying Instructor
Qualification	Flight Crew Instrument Flight Crew Flight Instructor
Experience	Flight Crew Last 90 Days 45 Flight Crew Total 2400 Flight Crew Type 700
Events
Anomaly	ATC Issue All Types Conflict NMAC Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Published Material / Policy

Narrative:

Aircraft X entered the right downwind. A helicopter was working in the right traffic pattern for a taxiway. The helicopter proceeded on the go for the right downwind. I issued traffic to aircraft X advising him about the helicopter. He reported the traffic in sight and entered the downwind and descended to 900 feet; which is below the pattern altitude for fixed wing as per the standard operating procedures. When aircraft X got on the ground they advised ground control that they had to make an abrupt maneuver to avoid the helicopter. I would advise the helicopter about aircraft X; and let aircraft X know that pattern altitude is 1;100 feet; so in future scenarios they don't descend into traffic that they reported in sight.

Original NASA ASRS Text

Title: BED Tower Local Controller and a flight instructor reported a descent below the published pattern altitude resulting in an NMAC.

Narrative: Aircraft X entered the right downwind. A helicopter was working in the right traffic pattern for a taxiway. The helicopter proceeded on the go for the right downwind. I issued traffic to Aircraft X advising him about the helicopter. He reported the traffic in sight and entered the downwind and descended to 900 feet; which is below the pattern altitude for fixed wing as per the Standard Operating Procedures. When Aircraft X got on the ground they advised ground control that they had to make an abrupt maneuver to avoid the helicopter. I would advise the helicopter about Aircraft X; and let Aircraft X know that pattern altitude is 1;100 feet; so in future scenarios they don't descend into traffic that they reported in sight.

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.

Bed tower local controller and a flight instructor reported a descent below the published pattern altitude resulting in an near midair collision.