WASHINGTON (Reuters) - The head of the Federal Aviation Administration told a U.S. Senate panel on Wednesday that Boeing ( BA ) must address a series of safety issues before he will let them boost 737 MAX production, warning the issue could impact company profits.

FAA Administrator Mike Whitaker capped production at 38 planes per month in January.

"They cannot grow to where they need to grow without" making broad safety improvements in six key categories, Whitaker said. "They don't do that, they don't grow, and if they don't grow, they're not going be able to achieve profitability."