The US Air Force issued Temporary Flight Restrictions near Havre, Montana on 12 Feb 2023, until 0020Z.
The region was near and overlapped with the pre-existing Hays MOA. Military Operations Areas are airspaces where military aircraft conduct various testing and training operations. At the same time, a US Air Force KC-135 was in the area.
The region included KHVR, the regional airport in Havre, which had been expecting Cape Air Flight 110 out of Billings at about dusk on Saturday afternoon. As a result of the flight restrictions, the flight returned to Billings. The plane had been in the air for about 24 minutes, and was roughly halfway to Havre, before it turned back.
Cape Air holds Essential Air Service contracts for several Montana communities and uses the Tecnam Traveller, a two-engine propeller craft that seats 9. The unpressurized plane typically operates at FL100 and most flights last less than an hour. It is usually operated by a single pilot. Among other things, that pilot would not want to run into a KC-135, or anything else being refuelled, while descending over the Bearpaw Mountains.
Traditionally if the MOA is active, that information is provided to the pilot at a pre-flight briefing, indicating that the Air Force’s operations Saturday night were either extremely urgent and/or not communicated to the FAA in the usual manner. An unidentified object flying between ground level and FL340 is not likely to be a weather-type balloon, unless the balloon is taking off or landing.