Jan 16 Reuters Boeing shares fell 4.1 on Tuesday and were set to extend last week39;s losses as the U.S. grounding of some 737 MAX 9 jets entered its 11th day, while the company39;s promise of further quality checks raised the specter of added costs.

The planemaker has been engulfed in a crisis since an Alaska Airlines MAX 9 jet made an emergency landing following a cabin panel blowout earlier this month, following which the U.S. Federal Aviation Administration FAA temporarily grounded 171 aircraft for safety checks.

Shares of beleaguered supplier Spirit AeroSystems, which made the fuselage for the affected jet, were also down 5.1 on Tuesday following last week39;s 14.1 loss. U.S. markets were closed for the Martin Luther King Jr. holiday on Monday.

The FAA said on Friday it will audit the MAX 9 production line and suppliers, and consider having an independent entity take over from Boeing certain aspects of certifying the safety of new aircraft that the regulator previously assigned to the planemaker.

With FAA taking a closer look into Boeing39;s production, we think the risk of productiondelivery impact increases significantly, Wells Fargo analyst Matthew Akers said, as he cut his rating on the planemaker39;s shares to equal weight from overweight.

Given Boeing39;s recent track record, and greater incentive for FAA to find problems, we think the odds of a clean audit are low.

Before Akers39; downgrade, 25 analysts had a buy or higher rating, while six had a hold…