Cowen on Wednesday lowered its rating of Boeing stock to market perform from outperform, citing the extended 737 Max crisis for piling on the company's costs and delaying production.
The note did not mention the crash of a Boeing 737-800 in Iran that killed all 176 people on board. That aircraft was not a 737 Max model and operator Ukraine International Airlines said the cause of the crash was not immediately known.
Cowen's downgrade comes a few weeks after Boeing replaced CEO Dennis Muilenburg with David Calhoun, a person who Cowen said is "a good choice for CEO." However, the firm said it believes Boeing's "turnaround will take time," as the company is working to recertify its 737 Max aircraft. Two 737 Max crashes within five months killed 346 people, resulting in the aircraft being grounded worldwide.
Boeing shares slipped 1.8% in trading Wednesday to close at $331.37.