Spirit's board is filling the COO position, which has been vacant since 2013, with an eye towards elevating the successful candidate to the top job when Lawson eventually retires, the sources said this week. They requested anonymity because the deliberations are confidential.

Lawson, who will turn 58 in March, has not yet determined his plans with the company, but his current contract ends in April, one of the sources said. It was not immediately clear how soon Spirit could hire a COO or how long Lawson would stay with the company, the sources said.

Lawson did not respond to queries about the matter. Spirit spokeswoman Debbie Gann said the company never commented on personnel matters.

Spirit, one of the world's largest aircraft parts makers and designers, is a major supplier to Boeing Co on its 737program, building 42 fuselages a month in Wichita, Kansas. It also makes fuselages for Europe's Airbus.

Spencer Stuart, one of the world's leading headhunter firms, is leading the search for a COO, the sources said. A Spencer Stuart spokesman declined to comment.

Lawson had been a longtime Lockheed Martin Corp executive before joining Spirit in March 2013. Company officials credit his data-driven analysis and hands-on management style for its revenue growth, cost cuts and a nearly tripling of its share price since then.

But Spirit's shares have underperformed in recent months, dropping 24 percent since August as investors grew increasingly concerned about the company's failure to reach a new master supply agreement with Boeing after more than two years of negotiations.

Industry executives and government officials who worked with Lawson said he might not be best suited for often tense negotiations with both Boeing and Airbus about large supply agreements. Pentagon officials had publicly blasted Lockheed for difficult negotiations on F-35 fighter contracts when Lawson ran that company's aeronautics division.

"Spirit can’t afford to alienate Boeing," said Loren Thompson, chief operating officer of the Virginia-based Lexington Institute, an industry-funded think tank. "Boeing holds all the cards, and it has the power of life and death over Spirit's future business."

Boeing and Airbus are both pressuring suppliers to lower costs as they battle for market share in a highly competitive global aircraft market.

Spirit was spun off from Boeing to a private equity group in 2005 before going public in 2006.

(Additional reporting by Alwyn Scott, Editing by Soyoung Kim and Lisa Von Ahn)

By Andrea Shalal