(Adds passengers seating, FAA investigation)
NEW YORK, April 23 (Reuters) - A day after three passengers lost consciousness on a commercial plane traveling from Chicago to Hartford, Connecticut, airline officials remained unclear on what had caused the travelers to pass out.
The pilot of SkyWest Airlines flight 5622, operating as United Express, began a rapid descent of the plane after learning that a passenger had passed out from possible cabin pressure issues, said airline spokeswoman Marissa Snow.
After making an emergency landing in Buffalo, New York, medics on the ground determined that two additional passengers sitting nearby had also lost consciousness, Snow said.
The airline said the three affected passengers had been seated near one another in rows 11 and 12 in the middle of the plane.
It is not known at what point the two other passengers lost consciousness.
All passengers on the plane, including those affected and 75 other travelers, were evaluated and released after landing.
Passenger Mary Cunningham, a registered nurse, said at least two people passed out before the plane began to descend, CBS-affiliate WIVBTV reported.
Other passengers reported to local media a frightening scene as the flight made an emergency landing.
No pressurization problem was found after maintenance staff and local authorities reviewed the aircraft, Snow said. Earlier media reports that a cabin door had opened, causing cabin pressure changes, were not true, Snow said.
The Federal Aviation Administration said on Wednesday that the crew on the Embraer aircraft had reported a pressurization problem and declared an emergency. The agency later amended its statement to omit mention of the pressurization problem. It is currently investigating the incident.
The National Transportation Safety Board is gathering information and determining whether to launch an investigation, NTSB spokesman Eric Weiss said on Thursday. (Reporting by Laila Kearney; Editing by Sandra Maler)