FILE PHOTO: A pilot waves as a Boeing 777X airplane taxis during its first test flight from the company's plant in Everett, Washington, U.S. January 25, 2020. REUTERS/Terray Sylvester

(Reuters) - Boeing Co BA.N shares tumbled as much as 22% to a more-than-six-year low on Tuesday following a rating downgrade that reflected its worsening cash flow due to the extended grounding of its 737 MAX jet and the blow from the coronavirus pandemic.

The stock was the biggest drag on the blue-chip Dow Jones Industrial Average .DJI index, shaving off 100 points.

Rating agency Standard & Poor’s on Monday lowered its credit rating on the planemaker to ‘BBB’ from ‘A-’ and now expects 2020 free cash flow in a range of negative $11 billion to $12 billion, down from a prior estimate of positive $2 billion.

Reuters reported last week that Boeing is set to draw down the full amount of a $13.8 billion loan, likely bringing its total debt to $41.1 billion.

Boeing’s total debt nearly doubled to $27.3 billion in 2019, as it grappled with additional costs related to the 737 MAX grounding and compensated airlines.

The company confirmed it is in talks with senior White House officials and congressional leaders for short-term assistance and a $50 billion bailout both for itself and the aviation sector.

At Tuesday’s low, Boeing’s shares are down about 74% since the fatal crash of an Ethiopian Airlines plane on March 10 last year.