Watch the skies: Here’s why there’s a low-flying helicopter buzzing over Boston this weekend

As the city gears up for the 127th annual Boston Marathon, security officials are conducting low-altitude helicopter flights over downtown and the Marathon route.

According to the U.S. Department of Energy’s National Nuclear Security Administration (NNSA), a twin-engine Bell 412 helicopter, which is equipped with radiation-sensing technology, will fly in a grid pattern at about 150 feet above the ground during daytime hours this weekend. 

The NNSA, which oversees the U.S. nuclear stockpile, nonproliferation, naval propulsion, and emergency response, uses the aircraft to measure expected background radiation to protect public health and safety on Marathon Day.

The chopper will travel at about 80 mph during the flyovers, which will take about two hours to complete each day. The flights began on Friday and will run through race day. 

“These surveys are a normal part of security and emergency preparedness activities. NNSA is making the public aware of the upcoming flights so citizens who see the low-flying aircraft are not alarmed,” the NNSA said in a press release. 

Morgan Rousseau

Morgan Rousseau is a freelance writer for Boston.com, where she reports on a variety of local and regional news.

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