Airline bosses on both sides of the Atlantic are lashing out at Boeing over a number of recent safety and production issues — loose bolts, a discarded wrench found under the floorboards, delayed shipments — as the crisis over the aircraft maker’s 737 Max 9 shows little sign of ending soon.

The ordeal is taking a toll. Boeing’s stock has fallen nearly 15 percent since Jan. 5, when a door plug flew off a Max 9 during an Alaska Airlines flight shortly after takeoff.

The Federal Aviation Administration grounded some Max 9 jets until they were inspected and said it would investigate whether Boeing failed to ensure that the plane was safe. (Here’s an explanation from The New York Times about how the door panel may have flown off that Alaska plane.)

Dave Calhoun, who became Boeing’s chief executive to right the company after fatal Max crashes in 2018 and 2019, is set to meet on Wednesday with senators, including Maria Cantwell, a Washington Democrat and chair of the Commerce Committee. Ms. Cantwell said last week that she planned to hold hearings on the Max 9 groundings.

Boeing’s customers have been vocal about their frustrations. “I am angry,” Ben Minicucci, the chief executive of Alaska Airlines, told NBC News on Tuesday after finding “many” loose bolts in its Max 9 checks. “My demand on Boeing is what are they going to do to improve their quality programs in-house.”

Scott Kirby, United Airlines’ chief executive, told CNBC on Tuesday that “the Max 9 grounding is probably the straw that broke the camel’s back for us.” He said the company was not sure whether it would get the Max 10 planes — a new airliner that has yet to be certified — that it had ordered any time soon. “We’re going to at least build a plan that doesn’t have the Max 10 in it,” Mr. Kirby said.

Airline bosses hope the tough comments will force Boeing to improve quality control and engineering. But they do not want to stoke panic about plane safety amid a sharp rebound in travel bookings over the past year. And there are not many alternatives to Boeing or its chief rival, Airbus.

Boeing’s woes will have a lasting impact. Mike Leskinen, United’s chief financial officer, told analysts that the groundings would dent growth in the “coming years.” Michael O’Leary, the chief executive of Ryanair, a low-cost European airline that is one of Boeing’s biggest customers, also has doubts that the Max 10 will be delivered soon.