The head of US industrial giant General Electric said Tuesday he remained "confident" in Boeing's 737 MAX aircraft, which has been grounded worldwide following two fatal crashes that killed 346 people.

"We are confident in the 737 MAX aircraft," said Larry Culp, chief executive of the firm that manufacturers engines for the popular aircraft.

"We're working closely with Boeing through the recertification process and, while the planes are on the ground, we're conducting proactive scheduled maintenance on the engines," he said during a conference call on the company's quarterly earnings.

But the company also said the crisis over the 737 MAX could dent revenues as the "timing of the MAX's return to service is uncertain."

"We have not changed our engine production plans at this time," Chief Financial Officer Jamie Miller said on the call.

"But the timing of cash flows may be impacted by collections of receivables from Boeing, depending on when aircraft deliveries resume. We will continue to adjust our operational managements as this situation evolves."

The company on Tuesday reported better-than-expected quarterly profits on improved performance in most industrial divisions, including aviation and oil and gas, suggesting a corporate turnaround was beginning to gain steam.

GE's share price surged nearly 7 percent as trading opened after the industrial conglomerate reported first-quarter profits of $3.5 billion, compared with a loss of $1.2 billion in the year-ago period.

At an investor conference this week, Boeing CEO Dennis Muilenburg was in the hot seat, facing tough shareholder questions over how the company designed and sought regulatory approval for the single-aisle 737 MAX aircraft.