Pilot reported a near mid air collision with a helicopter near hln airport.

Attributes
ACN	1668198
Time
Date	201907
Local Time Of Day	0601-1200
Place
Locale Reference	HLN.Airport
State Reference	MT
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Small Aircraft High Wing 1 Eng Fixed Gear
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	None
Flight Plan	VFR
Aircraft 2
Make Model Name	Helicopter
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Commercial Flight Crew Instrument Flight Crew Multiengine
Experience	Flight Crew Last 90 Days 258 Flight Crew Total 580 Flight Crew Type 258
Events
Anomaly	Conflict NMAC
Miss Distance	Horizontal 500 Vertical 0

Narrative:

Flying a survey line approximately 4 miles northwest of hln at 7400 ft. MSL. East to west lines. Monitoring tower frequency to give constant updates of our position near the airport. We were operating outside of the class D that ends at 6400 ft. MSL. We were advised there was helicopter traffic departing from hln. My camera operator was sitting in the right seat and advised me that there was a helicopter extremely close to us. Do not know the type of helicopter. I did not see the helicopter but the helicopter advised the tower seconds after my operator alerted me of a near miss with our airplane. Since I did not have visual before or after they advised a near miss I cannot estimate the distance between aircraft. Afterwards I asked my operator how close she estimated the helicopter to be and she could not determine but was at least closer than 500 ft. She explained she had seen the helicopter flying parallel to our flight path before turning towards us and calling the near miss.

Original NASA ASRS Text

Title: Pilot reported a near mid air collision with a helicopter near HLN airport.

Narrative: Flying a survey line approximately 4 miles northwest of HLN at 7400 ft. MSL. East to west lines. Monitoring Tower frequency to give constant updates of our position near the airport. We were operating outside of the Class D that ends at 6400 ft. MSL. We were advised there was helicopter traffic departing from HLN. My camera operator was sitting in the right seat and advised me that there was a helicopter extremely close to us. Do not know the type of helicopter. I did not see the helicopter but the helicopter advised the Tower seconds after my operator alerted me of a near miss with our airplane. Since I did not have visual before or after they advised a near miss I cannot estimate the distance between aircraft. Afterwards I asked my operator how close she estimated the helicopter to be and she could not determine but was at least closer than 500 ft. She explained she had seen the helicopter flying parallel to our flight path before turning towards us and calling the near miss.

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.