WASHINGTON, Sept 24 (Reuters) - Democratic Senator

Richard Blumenthal said the Federal Aviation Administration's

proposed $3.1 million fine against Boeing ( BA ) for a series of

safety violations is inadequate and wants the agency to explain

how it calculated the penalty.

"For Boeing ( BA ), such fines are easily absorbed as the

cost of doing business, not a meaningful deterrent to dangerous

behavior," Blumenthal wrote in a letter to FAA Administrator

Bryan Bedford. "Unless penalties rise to the level that forces

the company to invest in real safety reforms, the risks to the

flying public will persist."

The FAA found hundreds of quality system violations at the

planemaker's 737 factory in Renton, Washington, and Boeing ( BA )

subcontractor Spirit AeroSystems' ( SPR ) 737 fuselage factory

in Wichita, Kansas.