Boeing CEO Dave Calhoun speaks with reporters on Capitol Hill in Washington on Wednesday.

Boeing CEO Dave Calhoun said on Wednesday the planemaker will only support the operation of its airplanes if it is “100%” confident in their safety.

“We don’t put planes in the air that we don’t have 100% confidence in,” Calhoun told reporters in Washington before one of a series of meetings with US senators on the grounding of the company’s 737 Max 9 jets in the U.S. Calhoun added that Boeing fully understands “the gravity of the situation.”

The US Federal Aviation Administration (FAA) grounded most of those jets for checks after a plug replacing an unused exit door tore off an Alaska Airlines plane on Jan. 5, forcing an emergency landing.

Calhoun said senators had a lot of questions and vowed to be as transparent as possible in discussing the Alaska Airlines incident.

He referred a question about a Seattle Times report that Boeing had removed a component called a door plug that blew out on that Alaska Airlines MAX 9 to the National Transportation Safety Board (NTSB), which did not comment.

“We believe in our airplanes,” Calhoun said. “We have confidence in the safety of our airplanes.”

FAA Administrator Mike Whitaker told Reuters this month that the agency was “going through a process to work out how to restore confidence in the integrity of these plug doors.”

Boeing said on Tuesday it will hold a “quality stand down” on Thursday at the Seattle-area location where it makes the 737 MAX jets, pausing production and delivery operations for a day.

Calhoun will also meet with U.S. Senator Maria Cantwell, who chairs the Senate Commerce Committee. She said last week that she planned to hold a hearing after the FAA grounded 171 MAX 9 airplanes. A spokesperson for Cantwell said she was meeting with Calhoun at Boeing’s request.

Cantwell and Senator Ted Cruz, the committee’s top Republican, held a closed-door briefing last week on the grounding with FAA Administrator Mike Whitaker and NTSB Chair Jennifer Homendy. Cruz will meet with Calhoun on Thursday.

On Tuesday, United Airlines CEO Scott Kirby said the airline, which has ordered 277 MAX 10 jets with options for another 200, would build a new fleet plan that does not include a model already mired in regulatory and delivery delays.

Alaska Airlines CEO Ben Minicucci told NBC News the airline found “some loose bolts on many” Boeing 737 MAX 9 jets during inspections. The FAA is still reviewing data from an initial group of 40 planes.

The FAA’s Whitaker told CNBC on Tuesday that “it’s been difficult to predict, so we’ve sort of stopped trying ... But as soon as we get it sorted out it’ll be up again.”

Late on Sunday, the FAA urged operators of 737-900ER planes with the same door plug to immediately inspect them after some airlines had noted “findings with bolts” during maintenance inspections.

South Korean aero parts supplier KP Aero Industries said on Wednesday it plans to invest $20 million in a Vietnam factory to assemble components for Boeing planes, a move that would expand the U.S. aviation firm’s manufacturing network in the Southeast Asian country.

The U.S. aviation giant already has seven “sub-tier” suppliers - companies that sell components to its direct suppliers - in Vietnam.

In September, Boeing also reached a preliminary deal with flag carrier Vietnam Airlines for the sale of 50 Boeing 737 Max 8 jets.

Lee Young-su, a senior official at KP Aero, told Reuters the company would initially invest $20 million through 2028 to assemble components for Boeing 787 and 737 aircraft.

KP Aero will be formally granted later this week the authorisation to invest $20 million in Vietnam, authorities in the central city of Danang said in a media statement on Wednesday.

A Vietnamese official said the investment will be in the city’s high-tech industrial park.

KP Aero is a supplier of parts to Korean Air’s engineering division, which is in turn a direct supplier to Boeing.

Boeing deferred to KP Aero for comment.

South Korea’s aviation industry supplier KP Aero, which makes parts for Boeing planes, is set to invest $20 million in a factory in central Vietnam, local authorities said, in a move that could expand Boeing’s supply network in the country.

The U.S. aviation giant has said it is willing to expand its manufacturing network in Vietnam, where it already has seven “sub-tier” suppliers - companies that sell components to its direct suppliers.

In September, Boeing also reached a preliminary deal with flag carrier Vietnam Airlines for the sale of 50 Boeing 737 Max 8 jets.

KP Aero will be formally granted later this week the authorisation to invest $20 million in Vietnam, authorities in the central city of Danang said in media statement on Wednesday.