UPDATE 1-Spirit AeroSystems to add further inspections to Boeing 737 fuselage production -CEO

(Adds details from letter, background, Spirit comment, share price, in paragraphs 4-8)

By Valerie Insinna

WASHINGTON, Jan 16 (Reuters) - Boeing supplier Spirit AeroSystems will put in place additional inspections for its 737 fuselage production line following the mid-air cabin panel blowout of an Alaska Airlines 737 MAX 9 jet, Spirit's CEO said on Tuesday.

The new inspections will replicate what airlines will do to return Boeing Co's MAX 9 to service, CEO Pat Shanahan wrote in a letter to Spirit employees, which was seen by Reuters.

"One important takeaway is that we can take steps now to improve our first-pass quality," he wrote. "We must work in lock step with Boeing to enhance quality assurance and controls across our production system."

In addition to the inspections, Spirit will use the Federal Aviation Administration's safety management practices to guide manufacturing planning and audits, and issue visual instructions to employees to cut down the chance of rework, Shanahan said in the letter.

Spirit will also increase communication with its employees about its own quality management system, he said.

Spirit spokesman Joe Buccino declined further comment, saying, "This was an internal letter intended for the Spirit workforce."

The FAA grounded 171 MAX 9s earlier this month after a door plug manufactured and installed by Spirit was blown out during an Alaska Air flight.

Spirit AeroSystems shares were down 4.5% in midday trade. (Reporting by Valerie Insinna; Editing by Leslie Adler)