WASHINGTON (Reuters) - The U.S. Federal Aviation Administration said on Monday it would require inspections of Boeing 787 Dreamliners following an incident in March when a LATAM Airlines plane went into a sudden mid-air dive that injured more than 50 passengers.

The FAA said the apparent reason for the dive was the uncommanded movement of the captain's seat, which caused the auto-pilot to disconnect. The agency said it had received a total of five reports of similar problems with the captain and first officer seats on 787s, the most recent in June, and two remain under investigation.

The FAA's airworthiness directive impacts 158 U.S.-registered airplanes and 737 airplanes worldwide and requires airlines to inspect the captain's and first officer's seats on 787-8, 787-9, and 787-10 airplanes for missing or cracked rocker switch caps or for cracked switch cover assemblies within 30 days.

Airlines must perform any necessary corrective actions if issues are found.

The FAA said uncommanded horizontal movement of an occupied seat could result in a rapid descent of the airplane and serious injury to passengers and crew.

Boeing and LATAM Airlines did not immediately respond to requests for comment.

Separately, Boeing said Monday it had halted test flights on its 777-9 that is awaiting certification after a component between the engine and airplane structure was identified as failing to perform during a maintenance check.

The FAA said Boeing had informed it the company discovered a damaged component following a 777-9 flight test last week.

Boeing in July began certification flight testing of its long-delayed 777-9 with FAA regulators onboard after receiving Type Inspection Authorization.

Boeing added "no near-term flight tests were planned on the other flight test airplanes" and said the part is custom to the 777-9. (This story has been corrected to fix to Boeing 787-8 from 787-7, in paragraph 3)