WASHINGTON, Aug 6 (Reuters) - The U.S. National

Transportation Safety Board will question key witnesses from

Boeing ( BA ), Spirit AeroSystems ( SPR ) and the Federal Aviation

Administration on the mid-air cabin panel blowout of an Alaska

Airlines 737 MAX 9 door plug in January.

During the start of its two-day investigative hearing, the

board also plans to release documents including factual reports

and exhibits from the ongoing investigation.

The incident badly damaged Boeing's ( BA ) reputation and led to

the MAX 9 being grounded for two weeks, a ban by the FAA on

expanding production, a criminal investigation and the departure

of several key executives. Boeing ( BA ) has vowed to make key quality

improvements.

Boeing's ( BA ) senior vice president for quality, Elizabeth Lund,

and Doug Ackerman, vice president of supplier quality for

Boeing ( BA ), are among those who will testify during the hearings

scheduled to last 20 hours over two days, the NTSB said.

Terry George, senior vice president and general manager for

Boeing Program at Spirit AeroSystems ( SPR ), and Scott Grabon,

a senior director for 737 quality at Spirit, which makes the

fuselage for the MAX, will also appear, it added.

Last month Boeing ( BA ) agreed to buy back Spirit AeroSystems ( SPR ),

whose core plants it spun off in 2005, for $4.7 billion in

stock.

The hearing will review issues including 737 manufacturing

and inspections, safety management and quality management

systems, FAA oversight, and issues surrounding the opening and

closing of the door plug.

Boeing ( BA ) has said no paperwork exists to document the removal

of four key missing bolts.

Boeing ( BA ) and the FAA declined comment. A Spirit spokesperson

said the company "is fully committed to cooperating with the

NTSB in its investigation into this incident".

In June, FAA Administrator Mike Whitaker said the agency was

"too hands off" in its oversight of Boeing ( BA ) before January.

Also in June, the NTSB said Boeing ( BA ) violated investigation

rules when Lund provided non-public information to media and

speculated about possible causes.

The NTSB said Boeing ( BA ) would no longer see information

produced during the probe and, unlike other parties, will not be

allowed to ask questions of other participants during the

hearing.

Last month, Boeing ( BA ) agreed to plead guilty to a criminal

fraud conspiracy charge and pay a fine of at least $243.6

million to resolve a Justice Department investigation into two

737 MAX fatal crashes.