The twin-engine Huey, still guarding US missile fields half a century on. Live UH-1N positions.
The UH-1N is the twin-engine development of the Huey, and the US Air Force examples on this page are doing two jobs that keep them unusually visible: security patrols over the intercontinental ballistic missile fields in Montana, North Dakota and Wyoming, and VIP transport around Washington.
The missile field aircraft fly long, methodical patrols over open country, which is exactly the profile ADS-B picks up well — high enough and far enough from terrain to be heard. Serials in the 69- and 74- ranges give the fleet age away.
Replacement by the MH-139 Grey Wolf, a militarised AW139, has begun but is running years behind schedule.
It is a later member of the same family. The single-engine UH-1H is the aircraft most associated with Vietnam; the UH-1N is the twin-engine version that followed, and the airframes flying now date mostly from around 1970.
They provide security and response for the intercontinental ballistic missile silos spread across the northern plains. It requires covering very large, empty areas, which is why the tracks are so long.
The Boeing MH-139A Grey Wolf, based on the Leonardo AW139. Deliveries have been repeatedly delayed, so the Hueys continue.