Analysts at Bank of America Merrill Lynch downgraded Boeing's stock to "underperform" from "neutral" on Wednesday, citing concerns over the 787 Dreamliner's profitability over the long term.

"Boeing's current outlook assumes that the 787 will generate $29bn of cash by 1Q22, while our analysis shows that Boeing will only generate $14bn of cash. Boeing will likely take a charge on the 787 program and/or extend the block size," they said in a note Wednesday.

Boeing shares fell nearly 1.6 percent Wednesday and have dropped 9.7 percent this year. They were the biggest drag on the Dow Jones industrial average Wednesday.

The Dow component introduced the airplane in 2011, but has faced numerous production issues since then.