The National Transportation Safety Board quantified the obvious yesterday, reporting that more people died in U.S. airline accidents last year than in any year since 1977.

The board's annual aviation safety report said that U.S. carriers flying large airplanes -- those with more than 30 passenger seats -- had seven fatal accidents that killed 526 people. These included 197 fatalities on scheduled flights and 329 on unscheduled flights, 256 of them when the Arrow Air charter jet carrying soldiers home from Mideast peace-keeping duty crashed in Newfoundland last month.

The large-plane accident toll is the highest in a decade, and the fatality toll is second in U.S. aviation history to the 1977 toll, when 655 people died. Two chartered jumbo jets collided on the ground at Tenerife in the Canary Islands that year, killing 574 in the worst aviation accident in history.

Between the Tenerife collision and January of last year, there had been only five fatalities on chartered or unscheduled U.S. large-plane flights.

Accident rates for scheduled airlines flying large planes increased slightly last year in all statistical categories, including rates per million aircraft miles, per 100,000 flight hours and per 100,000 takeoffs. There were 18 nonfatal accidents and four fatal accidents, including the Delta Airlines crash in Dallas that killed 135 people.

Scheduled commuter airlines, which have become increasingly important in providing regular service to smaller communities, showed a slight improvement in their statistical record despite six fatal accidents that killed 35 people. A year earlier, 48 people died in seven fatal accidents.

There were a total of 17 commuter accidents, a record low and a 19 percent decline from the 21 accidents in 1984. The scheduled commuter industry continued a decade-long improvement in accident rates. In 1975, there were 3.3 accidents per 100,000 takeoffs; last year the rate dropped to 0.71 accidents per 100,000 takeoffs.

There were 77 fatalities in unscheduled, for-hire small planes last year, and 937 deaths in general aviation: business and pleasure flying. The fatalities were the lowest general aviation toll in 10 years and represent a continuing decline in fatality and accident rates for private and business aviation. The fatality rate was 1,556 in 1978.