Narrative:

I was pilot in command of an ec-130b4 conducting a [company] air tour flight from ZZZ to [a national park]. Four passengers were on board the aircraft plus myself. Prior to the flight; I conducted a pre-flight briefing and did not find any notams or airport recordings regarding area closures that would have alerted me to the situation I was about to encounter. Prior to my aircraft's departure; a us marshal prisoner transport plane was present on the ramp and not parked in its typical location; but much closer to the helicopter landing area and parking pads. The prisoner transport plane was in a parking place commonly used by other aircraft; so the presence of an aircraft at that location was not unusual. The us marshals' aircraft and officers had been present on the ramp for at least 15 to 20 minutes before [company] helicopters started departing the ramp. Two other [company] helicopters were also scheduled for departures and departed without incident about 5 to 10 minutes ahead of my aircraft; using the same departure. I lifted off the southern ramp parking pad and hover taxied to the helipad on the southeast corner of the ramp; the departure helipad used by [company]. Arriving at the helipad; I started a right 360 degree clearing pedal turn; looking above for inbound helicopter tour traffic. During the clearing turn I initiated contact with tower; requesting a...departure from the...ramp; which is standard procedure. In the midst of this call and with the helicopter passing through a northerly heading; I observed two men in plain clothes walking from the us marshal's aircraft toward my helicopter with what appeared to be ar-15 assault rifles pointed at the helicopter. The men waved me back with weapons pointed.... The men were approximately 100 feet from my helicopter and the us marshals' plane was approximately 200 feet north of my location.with guns pointed at my aircraft; I was concerned for the passengers' safety and backed the helicopter away from the armed men; repositioned; and landed near the [company] parking pads in an orientation where I could see further instructions from the men. During this repositioning I communicated my actions with the control tower and asked tower to have [local] police respond to my location in the interest of establishing communication and deescalating the situation. Police responded about ten to fifteen minutes after the request. While waiting for police to arrive; I remained at the controls with the helicopter running and stayed in communication with the tower. Once police arrived on scene; I shut down the helicopter and began offloading passengers.... I asked the officer to approach the us marshals and help establish constructive communication between me and the us marshals. The officer walked over to the us marshals and; when he returned; explained that the us marshals refused to speak with me. Shortly thereafter; the us marshals departed the area. The safety of my passengers; myself and any traffic in the vicinity was endangered; as during a clearing turn in a standard departure; I was forced to unexpectedly maneuver the helicopter in a low hover to gain distance from us marshals pointing assault rifles at the aircraft. There was no notice given that could have helped avoid this situation.

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Original NASA ASRS Text

Title: Helicopter pilot; doing a clearing turn on the ramp in the vicinity of a U.S. Marshal aircraft; was approached by two men pointing assault rifles at the helicopter. After a call for assistance to local police; the situation was resolved.

Narrative: I was pilot in command of an EC-130B4 conducting a [Company] air tour flight from ZZZ to [a National Park]. Four passengers were on board the aircraft plus myself. Prior to the flight; I conducted a pre-flight briefing and did not find any NOTAMs or airport recordings regarding area closures that would have alerted me to the situation I was about to encounter. Prior to my aircraft's departure; a US Marshal prisoner transport plane was present on the Ramp and not parked in its typical location; but much closer to the helicopter landing area and parking pads. The prisoner transport plane was in a parking place commonly used by other aircraft; so the presence of an aircraft at that location was not unusual. The US Marshals' aircraft and officers had been present on the ramp for at least 15 to 20 minutes before [Company] helicopters started departing the ramp. Two other [Company] helicopters were also scheduled for departures and departed without incident about 5 to 10 minutes ahead of my aircraft; using the same departure. I lifted off the southern ramp parking pad and hover taxied to the helipad on the southeast corner of the ramp; the departure helipad used by [Company]. Arriving at the helipad; I started a right 360 degree clearing pedal turn; looking above for inbound helicopter tour traffic. During the clearing turn I initiated contact with Tower; requesting a...Departure from the...Ramp; which is standard procedure. In the midst of this call and with the helicopter passing through a northerly heading; I observed two men in plain clothes walking from the US Marshal's aircraft toward my helicopter with what appeared to be AR-15 assault rifles pointed at the helicopter. The men waved me back with weapons pointed.... The men were approximately 100 feet from my helicopter and the US Marshals' plane was approximately 200 feet north of my location.With guns pointed at my aircraft; I was concerned for the passengers' safety and backed the helicopter away from the armed men; repositioned; and landed near the [Company] parking pads in an orientation where I could see further instructions from the men. During this repositioning I communicated my actions with the Control Tower and asked Tower to have [local] Police respond to my location in the interest of establishing communication and deescalating the situation. Police responded about ten to fifteen minutes after the request. While waiting for Police to arrive; I remained at the controls with the helicopter running and stayed in communication with the Tower. Once Police arrived on scene; I shut down the helicopter and began offloading passengers.... I asked the officer to approach the US Marshals and help establish constructive communication between me and the US Marshals. The officer walked over to the US Marshals and; when he returned; explained that the US Marshals refused to speak with me. Shortly thereafter; the US Marshals departed the area. The safety of my passengers; myself and any traffic in the vicinity was endangered; as during a clearing turn in a standard departure; I was forced to unexpectedly maneuver the helicopter in a low hover to gain distance from US Marshals pointing assault rifles at the aircraft. There was no notice given that could have helped avoid this situation.

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.