The sky was overcast and the temperature was in the 40s on that dreary November day when Mary Ann Renick, her daughter Desiree, 8, and friend Barbara Lane took off from Boston for a 3½-hour flight home to Clarksburg, W.Va.

Renick, a single mother, had never flown before. She and her daughter had traveled to Boston to discuss surgery for Desiree to correct her cleft palate. They were on a so-called angel flight, in which private pilots fly needy patients to distant medical appointments for free.

For a time, the trip was uneventful, but 90 minutes into the flight, three violent bumps shattered the reverie, Renick later recalled. Suddenly, the plane was coming apart at 10,000 feet and wind was roaring through the passenger compartment. Renick reached desperately for Desiree while fighting against her seat belt, which had wound around her neck and begun to strangle her.

"I kept struggling and struggling," Renick said. "I knew I was going to die."

But Renick and pilot Rolf Mielzarek survived when part of the plane's passenger compartment, left wing, and engine landed in a tree, leaving Renick suspended high above the ground.

Her daughter and friend weren't so lucky; both died from injuries sustained in the crash. Wreckage was strewn over an area two miles long and a half-mile wide. Afterward, the National Transportation Safety Board found that the plane's front nose assembly broke apart midflight, causing the crash in Lehman Township in the Poconos on Nov. 6, 1996.

But it wasn't the only Piper to break up midflight over the years.

The plane that Renick and her daughter flew in is one of hundreds of Piper Aircraft planes that have disintegrated midflight due to a design flaw the company has refused to acknowledge and correct, assert a team of Philadelphia plaintiffs' lawyers who have filed more than a dozen lawsuits against the company.

The lawyers say that a movable tail wing called a stabilator, which tilts up and down to aid the pilot in climbing or descending, is the cause of the crashes, and that Piper has sought to conceal the design defect by settling lawsuits with a stipulation that parties not discuss settlement details. Like other claims against Piper, Renick's case was settled.

Because the Piper stabilator is weakly reinforced, it is uniquely vulnerable to a self-reinforcing vibration called divergent flutter that can pulse through the entire aircraft and within seconds cause it to break apart. The lawyers contend that each crash exhibits the telltale signs of 45-degree folds in the horizontal stabilator, which occur as the stabilator first vibrates and then bends under stress.

The bending destroys the plane's aerodynamics, causing it to plummet from the sky.

"We have had a number of experts look at this, and all of them say the structure is too light and allows it to bend and change its airfoil," said Arthur Wolk, whose Center City-based firm has won more than $1 billion in jury verdicts and settlements in aviation lawsuits. "It is my view that,  given the history of these airplanes, the stabilator needs to go. If you have an engineering flaw, it will always rear its ugly head until you fix it."

Piper maintains that there is no merit to Wolk's allegations and that its aircraft are safe. The National Transportation Safety Board has filed reports on more than 200 midair breakups of Piper Cherokee, Saratoga, and Seneca aircraft since the 1970s, and in the vast majority of cases found that pilot error was the cause.

One common scenario, according to the NTSB: The pilot flew into or near bad weather, causing the aircraft to break apart.

But Piper points out that the NTSB never once has found that a design defect was the cause of a crash of these planes.

"All Piper aircraft are certified by the FAA," said Piper spokeswoman Jacqueline Carlon. "We are unaware of any lawsuit against Piper in which this supposed 'divergent flutter problem' has been identified by the NTSB as the cause of the accident. If the NTSB or the FAA thought there was such a problem, they would surely communicate it to the public."

The NTSB findings are viewed with skepticism by Wolk, himself an expert pilot certified to fly certain types of military jets, who contends that the NTSB is too in the thrall of aircraft manufacturers to objectively examine the causes of aircraft mishaps.

"As long as the National Transportation Safety Board continues to have the aircraft manufacturer as a party to the investigation, pilot error will always be the primary probable cause," says Wolk, who flies his own Eclipse 500 twin-engine jet once a month to California, where he has a second home.

Wolk is known as a tough litigator who doesn't shy away from difficult cases. He represented families of victims of the USAir Flight 427 crash in Pittsburgh on Sept. 8, 1994, that claimed 132 lives. Wolk lobbied hard for the NTSB to find that a flaw in the plane's rudder system caused the crash, while Boeing, manufacturer of the Boeing 737 that went down, argued pilot error was responsible. The NTSB eventually blamed the rudder. Wolk has been litigating the Piper cases since the 1990s.

"He is a guy who has to be taken absolutely seriously because he will do and spend whatever is necessary to prepare the case fully," said Ralph Wellington, a partner at Schnader Harrison Segal & Lewis, who as a corporate defense lawyer has tried multiple cases against Wolk. "He does not do anything by the seat of his pants."

Lawyers such as Wolk for years have been the bane of the general aviation industry, which after hitting a high in 1978 of about 18,000 aircraft manufactured declined to producing just under 1,000 planes in 1994.

Piper, which for years manufactured planes in Lock Haven, Pa., but closed all its facilities in Pennsylvania by the early 1980s, also was caught up in the decline, going in and out of bankruptcy.

It was a stunning fall for a company that once was an industry leader and whose planes were used to train most U.S. military pilots in World War II. It is now owned by the government of Brunei, a tiny oil- and gas-rich nation on the north coast of the island of Borneo, and headquartered in Vero Beach, Fla.

In 2016, it had sales of just over $150 million.

Industry leaders blame the decline in part on civil litigation and lobbied Congress successfully to pass the 1994 General Aviation Revitalization Act, signed by President Bill Clinton, which barred lawsuits against manufacturers for design defects on aircraft older than 18 years.

One of the bill's drafters, Victor Schwartz, then general counsel to the General Aviation Manufacturers Association, said liability-insurance premiums in the late 1970s and 1980s came close to destroying the industry. As manufacturers produced fewer and fewer planes, the soaring insurance costs were spread across a declining number of unit sales, and foreign manufacturers not faced with the same lawsuit exposure swooped in to scoop up market share.

"It was putting the companies out of business," Schwartz said.

Wolk says many of the accidents he's litigated occurred in good flying conditions, and he contends that the possibility of pilot error was remote. Such was the case in the 2013 crash of a Piper Seneca near Johnstown, N.Y., following a midair breakup. The pilot, who also was flying passengers on an angel flight, had taken pains to avoid inclement weather during the flight, said the lawsuit against Piper and other defendants.

The breakup of another Piper Seneca near Castro Verde, Portugal, in 2009 also occurred during good weather, another lawsuit says. An instructor and two student pilots were flying in clear weather at night when their aircraft disintegrated.

Portuguese aviation authorities later concluded that a phenomenon known as runaway trim caused the pilot, who had not been trained to deal with the problem, to lose control. But an expert working for the plaintiffs said in an affidavit that the aircraft likely crashed because its stabilator had failed.

"The accident is simply a repeat of many in-flight breakup events that have occurred scores of times in the same manner [i.e. loss of pitch control, loss of stabilator, bending or shedding of wings, and destruction of the fuselage of a stabilator-equipped Piper airplane]," Douglas O'Herlihy, a former NTSB air crash investigator and Coast Guard pilot with more than 17,000 hours of flying experience, said in an affidavit for the plaintiffs.

In-flight breakups, though rare, are typically catastrophic and only a few, such as Renick and Mielzarek, have survived. Another survivor was test pilot Sherman Hall, who gives a harrowing account of the breakup of his stabilator-equipped Seneca on Dec. 27, 1976, which he survived because he was equipped with a parachute.

Hall says that during the test flight to probe for flutter tolerances, he took the plane to 25,000 feet, high above the Cascade Mountain range in Washington state, pulsing the controls periodically to gauge the aircraft performance. The aircraft was in trim, meaning that its pitch and bank were well under control by the pilot, and all was functioning normally.

Suddenly, he said, "it was like an explosion."

The nose of the plane pitched downward, both wings sheared off, part of the tail section and rear door were gone, and the windshields had blown out. As the plane plummeted toward earth, gravity pinned Hall to the ceiling of the cabin, or what was left of it, and the violent shaking tore off his helmet. Cold air, minus-40 degrees Fahrenheit, blew into the cockpit.

Then, as suddenly as it had begun, the violent shaking stopped. Hall unbuckled his seat belt, slipped through the cockpit door, and began falling at about 20,000 feet as he pulled the cord on his parachute.

"I opened my chute immediately, which could have been fatal," he wrote. "As my chute opened, an engine with a section of wing came by from above. I can still see that engine clearly in my mind. The prop was feathered and the engine was running."

As Hall floated high above the Cascades' snowcapped peaks, he felt "awed by the destructive disintegration of that aircraft and my survival. There were small, light pieces of aluminum, fabric, and insulation floating down all around me. In any direction, I looked, it was like confetti."

Hall was soon on the ground. With his parachute rolled up under his arm, he stuck out his thumb and hitchhiked home.

Few have been so lucky.