GAITHERSBURG, Md. — Residents of a suburban community adjacent to a small, regional airport said they don’t give much thought to the jets that fly over their homes daily.

But the sound they heard Monday — a plane flying much too low and struggling to remain aloft — was different. It was followed by a horrifying scene on the ground.

A mother and her two young sons, one of them just a month old, were killed Monday morning when a private jet crashed into their two-story wood-frame home, which was engulfed in a fireball immediately, authorities and witnesses said. All three people on board the plane also died.

Marie Gemmell, 36, tried to protect 3-year-old Cole and 1-month-old Devon from the smoke and fire, but there was nothing she could do, Montgomery County police spokesman Capt. Paul Starks said. Her body was found in a second-floor bathroom, lying on top of her sons.

The jet’s fuselage crashed into the front lawn of an adjacent home, which was heavily damaged by fire, and investigators believe one of its wings, which had fuel inside, sheared off and tore through the front of the Gemmell home, said Robert Sumwalt, a National Transportation Safety Board member.

Witnesses reported seeing and hearing a secondary explosion after the plane hit the ground.