ANCHORAGE, DEC. 11 -- Last month's fatal crash of a heavily loaded commuter plane has federal authorities wondering whether Alaska's airplane passengers weigh more than passengers in the rest of the country.

The Federal Aviation Administration said Thursday it is asking the state's commuter airlines to weigh each passenger over a seven-day test period.

The FAA also ordered Ryan Air, owner of the twin-engine turboprop that crashed Nov. 23, to assume for now that the average passenger weighs 190 pounds, said FAA spokeswoman Ivy Moore. The accepted national average is 165 pounds, she said.

Moore could not offer a definitive reason why passengers in Alaska may weigh more, but said heavier clothing may play a role. "I think it's quite possible, especially in the wintertime," she said.

The Ryan Air crash at Homer, southwest of Anchorage, killed 18 people and injured three. The Beechcraft 1900, en route from Kodiak, was carrying its full capacity of 19 passengers and two crew members.

Investigators said the plane was loaded to within 100 pounds of its maximum acceptable weight with people and cargo.

When investigators weighed bodies and the crash's three survivors, they found the average weight to be 190 pounds, Moore said.

National Transportation Safety Board investigators have said they were studying the distribution of the plane's cargo and whether icing could have loaded down the plane even more.