FAA Knew of 757 Wake Danger : Aviation: Tests in 1991 showed airliner produced severe turbulence but no public warning was issued until after O.C. crash.

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The FAA had evidence dating as far back as October, 1991, that Boeing 757 jetliners cause unusually dangerous wake turbulence, but the agency issued no public warning until last month--after the deaths of 13 people in two plane crashes believed to have been linked to the 757 phenomenon.

The Federal Aviation Administration had previously said that it had indications of the problem since the beginning of last year. But documents obtained by The Times indicate that the agency had cause to be concerned long before FAA Administrator David Hinson issued a nationwide directive Dec. 22 that air traffic controllers begin issuing “wake turbulence” warnings to pilots landing behind 757s.

Wake turbulence occurs when a jet slices through the air, leaving a trail of horizontal cyclones that spring out from each wingtip. The turbulence can violently disrupt the air beneath planes following too closely behind.


Since the fall of 1991, at least two formal reports on the potential dangers were given to the FAA, in addition to anecdotal evidence gathered from pilots by the National Aeronautics and Space Administration:

* In October, 1991, two researchers who conducted wake turbulence studies on 757s at the FAA’s request told the agency the plane had caused more turbulence than any plane ever tested, even aircraft nearly four times its size. The researchers speculated that the plane’s uniquely designed fuel-efficient wing may have been the cause of the problem. They recommended that the FAA immediately require smaller planes be kept four miles behind 757s on final landing approach and that further testing be done.

When the most recent crash believed to be linked to the wake turbulence problem occurred--a Dec. 15 crash of a twin-engine corporate jet carrying two executives of the In-N-Out burger chain--the plane was about two miles behind the 757 as it prepared to land at John Wayne Airport and then went down. All five aboard perished.

* Also in October, 1991, the United Kingdom’s Civil Aviation Authority, the British equivalent of the FAA, presented a report at an FAA-sponsored symposium in Washington, saying the 757 had been involved in a higher proportion of wake turbulence-related incidents than other aircraft its size. Calling the 757 an “anomaly” among similar aircraft, the report said, “It is important to address the 757 problem.”

* Officials with the NASA-run Aviation Safety Reporting System, after collecting and reviewing 757 turbulence-related reports from pilots nationwide, brought the problem to the FAA’s attention twice in 1993: once in a teleconference call in January, and again in April at the quarterly meeting of the FAA’s own Air Traffic Procedures Advisory Committee.

“I can’t say that we were surprised” by the latest crash, William Reynard, head of the Aviation Safety Reporting System, said, referring to the Santa Ana accident. “The (conditions) were such that we felt there was a high probability that something was going to happen. That’s why we brought it up in the first place.”


Tony Broderick, the FAA’s associate administrator for regulation and certification, acknowledged that the FAA has had the data on 757 wake turbulence, but said there was nothing “alarming” about it. However, it was with no new information other than the two recent crashes that his boss, FAA Administrator Hinson, issued a bulletin Dec. 22 instructing the nation’s air traffic controllers to give “wake turbulence” warnings to planes landing behind 757s.

Broderick said the agency also has begun further testing of the 757.

Besides the Santa Ana accident, eight people were killed in December, 1992, when a twin-engine jet encountered 757 wake turbulence in Billings, Mont. Both crashes remain under investigation by the National Transportation Safety Board, but preliminary reports indicate that 757 wake turbulence played a significant role in each.

Two other incidents in the past year may also have been caused by turbulence from 757s, including the November crash of a single-engine Cessna in Salt Lake City in which three people were injured, and an instance over Denver in which a Boeing 737 experienced an “uncommanded roll” after encountering the wake of a 757.

According to researchers Leo Garodz and Kirk Clawson, they did wake turbulence testing for the FAA on a 757 on Sept. 25 and 26, 1990. The FAA had hired the National Oceanic and Atmospheric Administration to do the test. NOAA, in turn, called on Clawson, one of its own researchers, and hired Garodz, a decorated fighter pilot who had been with the FAA’s wake turbulence program for 20 years before retiring in 1986, as a consultant.

The tests were conducted in the NOAA vortex test facility near Idaho Falls, Ida., where such tests had been conducted for 20 years.

The tests were done because the FAA had no turbulence-related data for the new generation of twin-engine passenger jets, such as the 757 and 767, that took to the skies in the early 1980s.


What the researchers found out about the 757 both surprised and alarmed them: The narrow-body 757 appeared to cause more wake turbulence than any plane ever tested by NOAA, even military planes three and a half times its size. The 757’s wake speed of 326 feet per second--222 m.p.h.--was more than the winds generated by Hurricane Andrew.

At one point during the test, which involved flying a 757 past a 200-foot tower equipped with sophisticated electronic equipment, the force of the aircraft’s wake wrenched the equipment “out of its mounting socket”--a first in two decades of such testing, the researchers said.

The researchers issued a draft report of their findings in May, 1991. Although they didn’t issue the final version of their report until January, 1993, they presented their results publicly in October 1991 at the FAA’s International Conference on Aircraft Wake Vortices in Washington.

Speculating that the unusually high level of turbulence may be linked to the 757’s sleek wing and flap design, Garodz and Clawson recommended that smaller planes landing behind 757s be kept four miles behind and that heavier aircraft stay three miles behind on final approach. That recommendation--and another, that further testing be conducted--were ignored, the researchers said in interviews.

“We did not make (the recommendations) lightly,” Clawson said from his home in Idaho. “We felt that what the report did was bring it to the FAA’s attention. But they’re the regulatory agency. What happens after the report is up to them.”

Broderick from the FAA cautioned against lending too much weight to the NOAA report, saying “people make recommendations about all kinds of things. You have to evaluate . . . whether or not they are appropriate or make sense.” He said the data were not definitive.


At the same October, 1991, symposium that Garodz and Clawson presented their report, the United Kingdom’s Civil Aviation Authority also gave a report on wake turbulence, documenting incidents involving the 757 dating back to the early 1980s. The report said there was a disproportionate number of wake turbulence-related incidents involving 757s and advised that the matter be looked into.


In January, 1993, a month after the Billings, Mont., fatal accident, officials with NASA’s Aviation Safety Reporting System expressed their concerns about the problem in a teleconference call with FAA officials, according to Reynard, who runs ASRS.

Reynard said: “Starting back about this time last year we raised this issue in a telecon with the FAA . . . and discussed what we had been seeing in the reports coming in. We felt it needed to be pursued.”

Begun in 1976 at the FAA’s request, ASRS is managed by NASA and allows pilots and air traffic controllers nationwide to report mishaps and safety concerns confidentially. Reynard said it was founded to alert the FAA to potential problems before an accident happens because “it makes more sense to investigate something when it’s an incident, instead of waiting for an accident.”

ASRS officials brought the issue up again in April at the quarterly meeting of the FAA’s Air Traffic Controllers Advisory Committee, Reynard said.

“It was of a concern to us,” he said. “It struck us that here we had this information, that we had conveyed it, and nothing happened.”


The FAA’s Broderick downplayed the 2-year-old British report, saying: “We met with the British several weeks ago, and I’m sure they would have brought this up if they were alarmed.”

However, in retrospect, Broderick said, the FAA could have acted sooner in issuing the type of bulletin Hinson issued Dec. 22.

But even then, Broderick said, the measure was taken “out of an abundance of caution,” not because of any perceived danger to public safety.

Broderick said neither of the two accidents--the Santa Ana crash or the Billings, Mont., incident--would have happened if the pilots had followed basic rules of airmanship. Pilots are always told to fly above the path of a leading jet to stay out of its wake, Broderick said. Furthermore, he said, both pilots were flying under visual flight rules, which meant the pilots themselves, not air traffic controllers, were responsible for maintaining a safe cushion between their planes and the 757s in front of them.

“It is a matter of physics that if in fact a following airplane stays above the preceding airplane, the following airplane will never encounter the wake of the preceding plane,” he said.


Other aviation sources say that, at a minimum, the FAA was obliged to say what it knew about the 757’s dangerous wake turbulence so pilots could take extra precautions when landing behind them. At most, some people, including Garodz, believe the FAA should have mandated a three- or four-mile separation for aircraft landing behind 757s in all circumstances, at least until it conducted further tests.


“You can make recommendations in Washington for rule changes, but it can be very hard to get implemented,” Garodz said. A Princeton University graduate and former Navy pilot who flew in the Korean War, and received the Distinguished Flying Cross and the Air Medal, Garodz worked in the FAA’s wake turbulence program for 20 years. When he retired in 1986, he was the program manager. “The 757 had the most intense vortex system I’d ever measured.”

A national aviation source who requested anonymity because he works with the FAA on rule changes said: “There is kind of a common concern that it often takes a catastrophic incident before the FAA does anything.”

Similar criticism has been leveled at the FAA in the past year.

In April, after South Dakota Gov. George Mickelson was killed when the propeller on the small plane he was flying in failed, it was revealed that National Transportation Safety Board Chairman Carl Vogt had written the FAA in the months preceding the accident, urging mass inspections of that very propeller. As late as six weeks before the tragedy, Vogt told the FAA the flawed propeller could cause a “catastrophic accident.” The FAA responded that the propeller had flown millions of air miles without incident.

The revelation that there were previous warnings in that case prompted Sen. Larry Pressler, R-South Dakota, to call for congressional hearings on the FAA’s response, or lack of a response.

The FAA subsequently ordered the replacement of propellers on all planes like the one involved in the crash that killed Mickelson and seven others.


While tests on the 757 are under way, those in the industry speculate that the aircraft’s unique wing design may be the biggest reason it produces so much more turbulence than other planes its size. Unlike most aircraft, whose flaps are cut into sections, the 757’s wing flaps are one solid piece. That means there is no place for the air to escape as it travels along the base of the wing gaining speed and momentum.


But it’s that very design, experts say, that makes the 757 among the most fuel-efficient and quiet commercial passenger jets ever made.

Boeing spokeswoman Elizabeth Reese said the 757 has been in service since 1982 and only recently had the wake turbulence problem been cited in any accident. This year alone, she said, the worldwide fleet of 574 757s have, collectively, logged 7 million safe hours in the air, traveling 2.7 billion miles and making 3.5 million landings.

“It hasn’t been an issue and the aircraft has been in service for 10 years,” Reese said.

The NTSB, which is investigating both the crashes in which 757 turbulence is believed to have been a factor, has asked the company for whatever data it has on 757 wake turbulence, Reese said. She said the company is cooperating “in the interest of aviation safety.”

Times librarian Sheila Kern contributed to this report.

Dangerous Wake Since 1991, studies have shown that a Boeing 757 causes more wake turbulence than planes even 2 1/2 times larger. How wing design differences affect turbulence of a 757 and a Boeing 747: *Boeing 757 Large wake turbulence: Long, continuous flap generates horizontal tornadoes that can violently disrupt the air around planes following too closely; in some cases, the FAA requires small planes to stay at least four miles behind a 757 *One long flap Boeing 747 Smaller wake turbulence: Shorter, double flaps create mini-tornadoes; strength of turbulence diminishes quickly as the pairs of mini-tornadoes collide with each other; turbulence diminishes 1 to 1 1/2 minutes downstream *Two shorter flaps Source: Leo Garodz, aerodynamicist; Researched by CAROLINE LEMKE / Los Angeles Times