A firefighter stands outside a smoldering house where a small private jet crashed in Gaithersburg, Md., Dec. 8, 2014. Marie Gemmell and her two young sons inside the home and three people on the aircraft were killed. (Jose Luis Magana/AP)

Ice on the wings brought down a twin-engine private jet that crashed into a Montgomery County house in 2014, killing three people onboard and a mother and two children who lived in the house, according to the findings in a detailed report released by the National Transportation Safety Board on Wednesday.

If the pilot, Michael Rosenberg, had turned on the plane’s de-icing system before he approached Montgomery County Airpark in Gaithersburg, he probably would have received a stall warning in time to avoid crashing into a development a half-mile from the runway, the agency said.

Rosenberg, 66, two of his passengers and the mother, Marie Gemmell, 36, and her children died when the plane crashed into the house and exploded in flames Dec. 8, 2014.

The NTSB said that “weather data indicate that the accident flight encountered clouds and was exposed to structural icing conditions while descending into the Gaithersburg area. There were numerous reports of ice from pilots flying in the area, and the accident pilot indicated that he was still in the clouds almost 15 minutes after entering them.”

The NTSB report said “had the ice protection been activated the pilot would have received an aural warning of impending stall about 20 seconds earlier.”

NTSB investigator Brian Rayner peers into the cargo door opening on the fuselage of the plane that crashed into a house in Gaithersburg, Md. (Michael S. Williamson/The Washington Post)

The Embraer EMB-500/Phenom 100’s twin jet engines continued to function normally, but the plane slowed too dramatically to reach the runway. With its flaps extended and landing gear down on final approach, the plane should have been flying at 120 mph. The cockpit data recorder showed it was going 101 mph in the final seconds of flight.

As it approached the Gemmell home, the plane went into an aerodynamic stall, with its tail sharply down and nose elevated. At that angle, normal air flow to keep it aloft ceased, and the plane lost its ability to fly.

In the final 20 seconds before the crash, according to the cockpit voice and data recorder, an automated warning in the cockpit chanted “stall-stall, stall-stall” 13 times in staccato rhythm.

One of his passengers responded, “Oh, no!” while the other said, “Whoa, Whoa.”

The plane was completing a bumpy 57-minute flight from Chapel Hill, N.C., near the Durham headquarters for Rosenberg’s medical research firm.

As it flew through Northern Virginia and into Maryland, other pilots were reporting ice attempting to form on their wings as they flew through clouds between 4,000 feet and 5,500 feet altitude.

Rosenberg turned on the plane’s de-icing system for more than two minutes as it reached its 23,000-foot cruising altitude, but then he flicked if off again for the remainder of the flight.

It remained off as he began to descend toward Gaithersburg, despite flying through clouds again.

The NTSB said that may have been a fatal mistake: “That puts the airplane in visible moisture, an essential element for ice, for approximately 15 minutes.”

[Jet plane pitched and rolled before hitting Maryland house]

Rosenberg was a highly qualified pilot, with 4,500 hours logged in control of an aircraft. He was certified as a commercial pilot and as a flight instructor. He also was rated to fly the Phenom, a sophisticated six-passenger jet that costs more than $4 million and can fly in excess of 400 mph.

But the 2014 incident was the second time that Rosenberg crashed while attempting to land at the Gaithersburg airport. Four years earlier, stall warnings sounded as he touched a single-engine turboprop plane down on the runway. When the plane drifted to the left side of the 75-foot-wide runway, Rosenberg attempted to lift off again to circle the airport for a second landing attempt.

Instead, the plane went about 100 feet to the left and crashed into trees. He escaped with a minor injury. The NTSB concluded that the cause was pilot error.

More than 1,000 small planes crash in the United States every year, and hundreds of those crashes result in fatalities, but few achieve the horrible distinction of what happened in Gaithersburg on the Monday morning of Dec. 8, 2014.

The calls began flooding into the 911 dispatcher at 10:42 a.m.

“We heard a giant explosion. . . . It looks like a house is on fire. . . . We got some people running over there to see if people are okay.”

People were not okay.

[Plane crash in Gaithersburg shattered picture of a happy family]

Rosenberg and his passengers — David Hartman, 52, and Chijioke Ogbuka, 31 — were dead. And a fire, helped along by an explosion of jet-fuel, was closing in on Marie Gemmell, 36, her son, Cole, 3, and infant, Devin. They were huddled in a second-floor bathroom — one child in Gemmell’s arms, the other tucked between her legs.

Small planes have crashed into houses or buildings in the United States over 110 times since 2000, but most of the more than 120 deaths have been pilots or passengers, not people in the sanctuary of their home.

Another call came into 911 at 10:44 a.m.:

“I just saw a jet hit a house near Montgomery Airport. When he came in on final [approach], he flamed out and went straight down into that house.”

The four-bedroom house at 19733 Drop Forge Lane sits on a cul-de-sac a bit more than a half-mile from the end of the airport runway. It is in Hunters Woods, one of many neighborhoods that developed over the years around an airport that was surrounded by farmland when it opened in 1959. The frame house with white siding, a two-car garage, a deck in the back and a tree planted in the front, was built in 1982.

[Gaithersburg grew and swallowed its semi-rural airpark]

Two years later, after several fatal plane crashes, a headline in The Washington Post read, “Some critics say it’s an accident just waiting to happen.” The 1984 article quoted a man who lived nearby: “It’s inevitable that a plane will fall out of the sky.”

That did not happen with the tragic consequences that the man envisioned until 30 years later. People who live in Hunters Woods have developed a certain expertise about small planes after years of watching them take off and land.

One of them was a man who was standing in his driveway and saw the jet go down. His call to 911 gave the first inking of what had gone wrong aboard the plane:

“I watched it go over. It was wobbling from side to side.”

The blue-and-white wreckage of the airplane tumbled into the front yard. The house, as firefighters are prone to say, was “fully engaged” by flames. Gemmell and her children were overcome by smoke and died.