Workers studied the wreckage of the helicopter that went down in the Hudson River after it was struck by a small plane.

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Roughly 15 years ago, the federal agency that investigates air disasters made a plea for more data on the air-tour industry, to improve safety for helicopter, airplane, balloon and airship flights around the nation. Six years later, it asked again.

In 2007, the agency, the National Transportation Safety Board, told the Federal Aviation Administration that it wanted to require air-tour operators to track complaints about pilot performance. This year, it said instruments to track a flight’s vital signs — flight data recorders — should be customary in helicopters and other tour aircraft, to aid in investigating fatal accidents.

To date, however, none of those recommendations have been carried out, according to safety board officials. And when the F.A.A. or other government regulatory agencies have acted, the board said, it has taken them years to do.

Deborah A. P. Hersman, the safety board chairwoman, in an interview Thursday sharply criticized a process that, she said, sometimes takes “2 years, 4 years, 10 years” to see the board’s recommendations achieved.

“We issue them because we think they can save lives and improve safety,” Ms. Hersman said of the board’s recommendations. The board does not have the authority to carry out or enforce its recommendations.

A safety board team was back at work Saturday, this time investigating the midair collision between a small fixed-wing airplane and a New York sightseeing helicopter over the Hudson River. The safety board, its officials have made clear, is all but sure to make another set of recommendations specific to this crash, which killed nine people.

But the history between the safety board, an advisory body set up by Congress four decades ago, and the F.A.A., which regulates planes, pilots and airlines, suggests that any changes may not happen quickly.

“To its credit, the N.T.S.B. makes lots of recommendations after each incident, and in fairness, the F.A.A. cannot expeditiously act on every one of those,” said Patrick Smith, a commercial airline pilot and aviation author. “Now, having said that, the F.A.A. does tend to be slow moving on certain issues.”

Laura J. Brown, an F.A.A. spokeswoman, said that there had been fewer accidents in the air tour industry over the years.

“We have steadily improved air tour safety,” she said.

Sometimes, to be sure, the F.A.A. can move quickly.

It did so in 2006, when it tightened air restrictions above the East River “within two days” after the New York Yankees pitcher Cory Lidle and his flight instructor were killed when their plane crashed into a building, Ms. Brown said. “We issued the change before they issued the recommendations,” she said. “But there are other situations that require rule-making.”

She said the agency was considering an immediate reaction to the Hudson crash: making it mandatory for pilots in the uncontrolled air corridor to announce their location and intentions on a common radio frequency whose use is now voluntary.

“We welcome their taking some action, but we certainly don’t feel it goes far enough, said Robert M. Gottheim, district manager for Congressman Jerrold L. Nadler, a Democrat who represents the West Side of Manhattan.

A review of 15 years of interaction between the safety board and the F.A.A. over the air-tour industry, and its pilots and practices, reveals a slow-moving process.

The safety board and the F.A.A. have a long history of being frustrated with each other in matters involving major airliners or crashes of commercial jetliners, and there are various theories about why. On the one hand, the safety board sometimes proposes fixes that require technological advances or are viewed as too costly. On the other, the F.A.A. is sometimes criticized as working too closely and protectively with the airline industry.

In this case, the friction is arising over the much smaller air-tour industry — which involves an uncertain but limited number of daily flights for purposes like tourism or recreation and carries an estimated two million passengers a year, compared with the roughly 70,000 daily commercial airline flights that move 550 million passengers a year.

In 1995, the safety board undertook its most rigorous study of the air-tour industry, examining 139 accidents from Alaska to Hawaii to Maine. It called for certain steps to be carried out nationally: to gather more data on the numbers of air-tour operations and to ensure flight safety in scenic or closed-in areas, which suggests regulating airspeed in some cases and flying altitudes in others.

But the recommendations that it issued in a final report on improving safety took years to negotiate and were never carried out to the board’s satisfaction.

“We know how many accidents there are, but we don’t know how many flights there are,” Ms. Hersman said. “They are trying to make improvements, but we would like to see better data, and that would help us do more appropriate risk analysis.”

Ms. Brown, of the F.A.A., could not immediately address all of the safety board’s complaints about each recommendation.

She said Saturday’s crash was the first midair collision involving an air tour helicopter since 1998. And, after the agency put into practice new safety rules for the industry in 2007, the number of air-tour crashes fell to 8 annually from an average of 13 a year over the previous five years, Ms. Brown said.

It has not been determined whether any of the prior recommendations made by the safety board would have applied to the flights involved in the midair crash in New York. But some people think they would have.

“In the air-tour industry, we had problems in New York and in Alaska and over the Grand Canyon, but it was certainly not isolated,” said James E. Hall, who was the safety board chairman who oversaw the 1995 study.

After investigating the midair collision of two helicopters in Phoenix in July 2007, the safety board issued a call for crash-resistant flight recorder systems to become common equipment on a wide variety of aircraft, including touring helicopters.

Despite their importance, flight recorders and cockpit voice recorders have proved difficult to justify by certain cost-benefit analyses, Mr. Hall said.

Ms. Hersman and Matthew S. Zuccaro, the president of the Helicopter Association International, agreed that newer technology for helicopters could cost up to $12,000 per unit and roughly $40,000 for older models.

In the end, said John J. Farmer, the former New Jersey attorney general who served as the senior counsel to the 9/11 Commission, fixes sometimes take time.

“I think you have to avoid the temptation every time an accident occurs to think there is a systemic fix that will prevent any kind of similar actions from occurring in the future,” he said.

Colin Moynihan contributed reporting.