The eerie coincidence of the two "inland" flights crashing into water near busy downtown airports--in Washington and then in Boston--has renewed the controversial debate over airline water safety.

Both airplane accidents demonstrate a major shortcoming of present Federal Aviation Administration regulations. Neither plane, according to the FAA's definition of "overwater flight," was flying over water. Standard overwater safety measures--life vests--are required only on planes flying 50 miles out to sea. Stringent measures--the use of life rafts--are only taken when planes fly 162 miles out to sea.

But 95 percent of all airline water crashes are not out at sea. They occur on landing and takeoff at the 200 U.S. airports situated near large bodies of water, according to the Air Line Pilots Association. Since 1960, more than 40 planes (an average of two a year) have crashed into water. ALPA argues that 70 percent of those flights, like the Boston crash, are survivable. What kills passengers, Matt Finucane, director of Ralph Nader's Aviation Consumer Action Project, explained, is not the impact of the crash but faulty or nonexistent water-safety equipment.

Nader's Aviation Consumer Action Project called on the FAA last week to require all airlines to carry life vests that can be put on in 15 seconds. Passenger planes are now allowed to fly over water with only floatable seat cushions.

The U.S. Coast Guard does not approve these cushions for children and non-swimmers. To use one properly, a person must hold it across his chest while floating in the water on his back. Most airlines don't explain this fact on the pocket safety card, nor do they explain that some cushions lose their buoyancy after 10 minutes. Manufacturers of the floatable seat cushions say that providing more buoyancy would make them flammable during fire conditions. Floatable seat cushions also force a passenger's head into the water making the user more susceptible to kerosene ingestion.

Use of the floatable seat cushions can lead to hypothermia, since most bodies of water in and around the United States are quite cold. Many of the passengers who survived the Boston and Washington accidents suffered from this condition.

There were life vests aboard both the Air Florida and the World Airways flights. But the National Transportation Safety Board says these vests have not been upgraded since World War II, are too difficult to put on and often are stored under seats that collapse on impact with water. ALPA wants upgraded life vests to be placed in seat backs so they can be retrieved faster. That location, where vests could be seen easily by flight attendants, may also prevent pilferage--600 life vests a month are stolen from some air carriers.

Life rafts offer the best way to keep a person out of water and maintain the body temperature essential to survival, according to Wayne E. Williams, director of the Institute for Survival Technology in Dania, Fla. But air carriers are allowed to fly as far as 162 miles from land without rafts. Some carriers, including Air Florida, want that limit extended to 400 miles because the added weight of rafts increases fuel costs.

Removal of four 42-person rafts from a 727-200 makes the plane 500 pounds lighter, and results in saving about 10,000 gallons of fuel a year, the FAA says. Any modern aircraft, the agency says, can fly 162 miles to shore on a single engine. But what happens if a raft-less plane crashes in water--no matter how many engines are working?

A life raft may not have saved lives in the Air Florida crash. But in two other cases --one near Los Angeles and one near San Francisco--life rafts were used to keep passengers afloat until rescuers reached them. In 1978, when a National Airlines plane, from which the rafts have been removed only days before, went down near the Pensacola, Fla., airport, three people drowned in the warm water because of kerosene ingestion.

The Aviation Consumer Action Project has asked the FAA to improve airline water-safety equipment within six months. In addition, the NTSB will soon make safety recommendations in response to the Boston and Washington accidents. It remains to be seen whether the FAA will respond.

It was a little over a year ago that the FAA, in rejecting calls for better airline water safety equipment, said the possibility of any airplane crash is "very remote" and the possibility of an airplane crash into water is "even more remote."