By Valerie Insinna

WASHINGTON (Reuters) -Boeing early on Monday shared instructions with airlines for inspecting the 737 MAX 9 fleet, the company confirmed, after 171 MAX planes were grounded by U.S. regulators on Saturday following an accident where a cabin panel ripped off an Alaska Airlines jet while in mid-air.

The instructions, known formally as a multi-operator message, are a key step to allow airlines to complete or certify inspections have been conducted that comply with the Federal Aviation Administration's directive that would allow them to put planes back in service.

"We agree with and fully support the FAA’s decision to require immediate inspections of 737-9 MAX airplanes with the same configuration as the affected airplane," Boeing (NYSE:BA) Commercial Airplanes head Stan Deal said in a letter to employees.

"Our teams have been working diligently – with thorough FAA review – to provide comprehensive, technical instructions to operators for the required inspections," he said. "This morning, our team issued the instructions via a multi-operator message."

The message was delivered to airlines around 3 a.m. Pacific Time (1100 GMT), a source told Reuters, who was first to report that Boeing had sent the instructions.

The U.S. Federal Aviation Administration (FAA) did not immediately comment but a source said it signed off on Boeing's instructions to airlines.

Boeing is "working closely" with MAX 9 customers and providing technical assistance, while staying in contact with the FAA, Deal said.

Boeing plans to hold a "short factory stand down" during the Monday morning meetings at the Renton, Washington-facility that makes the MAX, Deal said. Boeing CEO Dave Calhoun will host an internal Boeing webcast for employees on Tuesday.

Alaska Airlines did not immediately comment.

The FAA on Saturday ordered the temporary grounding of 171 Boeing MAX 9 jets after a door plug tore off from a brand-new MAX 9 shortly after it took off from Portland, Oregon.

On Sunday, the U.S. regulator said the affected fleet of Boeing MAX 9 planes, including those operated by other carriers such as United, would remain grounded until the regulator was satisfied they were safe.

Boeing shares were down 6.6% in Monday trading, though off the day's lows.