R44 instructor reported a precautionary landing in a field due to power fluctuations.

Attributes
ACN	1473503
Time
Date	201708
Local Time Of Day	1201-1800
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	Robinson R44
Operating Under FAR Part	Part 91
Flight Phase	Cruise
Route In Use	None
Flight Plan	None
Component
Aircraft Component	Engine
Person 1
Function	Instructor Pilot Flying
Qualification	Flight Crew Flight Instructor Flight Crew Commercial Flight Crew Instrument Flight Crew Rotorcraft
Experience	Flight Crew Last 90 Days 90 Flight Crew Total 1450 Flight Crew Type 415
Events
Anomaly	Aircraft Equipment Problem Critical

Narrative:

While transitioning back to [departure airport]; the engine started making a loud banging noise. I scanned the instrument cluster and saw the RPM's surging and manifold pressure spiking. I decided that we could not make it back to [departure airport] and lowered collective and picked a field to land in to check it out. I make an expeditious descent and land with power at the bottom with no other damage to the helicopter. Upon landing I saw white smoke coming from behind us; so I told my student to get out and see if we are on fire as I rapidly shut down the helicopter and pull fuel. There was no fire; just smoke from oil burning on the muffler.

Original NASA ASRS Text

Title: R44 Instructor reported a precautionary landing in a field due to power fluctuations.

Narrative: While transitioning back to [departure airport]; the engine started making a loud banging noise. I scanned the instrument cluster and saw the RPM's surging and manifold pressure spiking. I decided that we could not make it back to [departure airport] and lowered collective and picked a field to land in to check it out. I make an expeditious descent and land with power at the bottom with no other damage to the helicopter. Upon landing I saw white smoke coming from behind us; so I told my student to get out and see if we are on fire as I rapidly shut down the helicopter and pull fuel. There was no fire; just smoke from oil burning on the muffler.

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.