US lawmakers are calling on federal regulators to ground Boeing's 737 Max 8 after the plane model was involved in its second deadly crash in less than five months.

Sen. Dianne Feinstein, a Democrat representing California, asked the Federal Aviation Administration to ground the plane until an investigation could be completed.

"I write to ask that all Boeing 737 Max 8 series aircraft be grounded until their safe use has been confirmed," she said in a letter to the air-safety agency on Monday, citing the similarities between Sunday's crash of Ethiopian Airlines Flight 302 and the Lion Air disaster from October.

"Continuing to fly an airplane that has been involved in two fatal crashes within just six months presents an unnecessary, potentially life-threatening risk to the traveling public," Feinstein added.

While a handful of countries, including the United Kingdom, China, and Australia, have grounded the plane pending further investigation into the latest crash, the United States has not.

The FAA said on Monday evening that the plane was still safe for flight and that there was no data to "draw any conclusions" between the two disasters.

Still, the agency recommended design changes to the airplane as well as updates to its training requirements and operations checklists. Fifty-nine airlines around the world operate the plane, according to the FAA.

Other lawmakers pushing the FAA to temporarily ground the aircraft include Democratic Sen. Richard Blumenthal of Connecticut, the presidential candidate Sen. Elizabeth Warren, Mitt Romney, Ted Cruz, and Rep. Peter DeFazio, a Republican from New York.

President Donald Trump also weighed in on the crash Tuesday morning, calling some new planes "too complex to fly," despite years of technological upgrades to passenger aircraft that have been proven to make flights safer.

"Airplanes are becoming far too complex to fly," he tweeted. "Pilots are no longer needed, but rather computer scientists from MIT. I see it all the time in many products. Always seeking to go one unnecessary step further, when often old and simpler is far better."

He added: "All of this for great cost yet very little gain. I don't know about you, but I don't want Albert Einstein to be my pilot. I want great flying professionals that are allowed to easily and quickly take control of a plane!"

More about the Boeing 737 Max 8 and the Ethiopian Airlines disaster: