HOLLAND, Mich. -- Capt. Robert Lind struggled to keep the DC-4 aloft during the raging thunderstorm as the airliner approached southern Lake Michigan from the east.

Strong winds and frequent lightning had knocked out the power that evening along much of the lake's southeastern coast, from Holland down to Benton Harbor.

Three pilots who had taken off from Detroit turned around because of the turbulence they encountered at the edge of the fierce storm.

Lind had taken off a few hours earlier from New York's LaGuardia Airport. Northwest Airlines Flight 2501, carrying 55 passengers and three crew members, was scheduled to arrive the next morning in Seattle after making stops in Minneapolis and Spokane, Wash.

It never made it.

Flight 2501 crashed into Lake Michigan late on June 23, 1950, killing Lind and the 57 others on board. At the time, it was the deadliest airliner accident in the nation's history.

While a Coast Guard cutter found most of the debris in the water about 18 miles north-northwest of Benton Harbor, no one is certain exactly where the plane went down.

Within a couple weeks of the crash, some partial human remains washed ashore near South Haven, Mich., which is about midway between Holland and Benton Harbor.

Next month, Valerie and Jack van Heest and their nonprofit group, Michigan Shipwreck Research Associates, will resume their nearly 3-year-old search for the crash site. They hope to find at least one of the plane's four engines intact.

"We have a much greater chance of narrowing down the area this year than we ever have in the past," said Valerie van Heest, 46, who has put her marketing and graphic design career on hold to focus on the search. She's also trying to contact victims' relatives to make them aware of her group's efforts.

The hunt will take place about 15 to 20 miles off the coast of South Haven, in the same general area of the lake where the van Heests' group previously located the well-preserved remains of a historic, 208-foot-long steamer, the Hennepin, upright in 230 feet of water.

The Holland-area couple has the financial backing of best-selling adventure novelist Clive Cussler, who learned through a 2004 newspaper article about their interest in locating the plane crash site and called to offer his support, van Heest said.

Cussler founded a nonprofit group in 1979 called the National Underwater Marine Agency to aid in the discovery of historically significant shipwrecks and the preservation of their artifacts. Its most significant discovery probably was the Confederate submarine Hunley, found in 1995 buried in silt and sand near Charleston, S.C.

The van Heests started searching for Flight 2501 in the fall of 2004, aided by sonar expert Ralph Wilbanks, whom Cussler provided. They conducted additional searches in May 2005 and again last May.

"It is a good mystery. Nobody's quite sure exactly what happened and it certainly was a significant tragedy in its day," said Dirk Cussler, who has co-authored a couple of books with his father and runs their shipwreck group.

The accident-investigation report released Jan. 18, 1951, by the Civil Aeronautics Board said "there is not sufficient evidence upon which to make a determination of probable cause." Investigators found only small pieces of debris -- seat cushions and arm rests, clothing, blankets, pillows, pieces of luggage, plywood flooring and the aircraft's log book -- and concluded that the DC-4 "struck the water with considerable force."

Van Heest said she has found the representatives of 20 of the families who lost loved ones. It's important to her that she reach as many as she can.

"I don't want anything out of this except the satisfaction of helping them come to grips or closure or whatever you would call it with this accident," she said.

Bill Kaufmann was 6 years old when his mother, Jean, was killed in the crash. Now 63 and an attorney with a law practice in Oakland, Calif., Kaufmann said he doesn't expect much to come from the latest search but he hopes that they will find something -- anything -- that would provide him with some answers.

"I'd like to know what happened," Kaufmann said.

He and the relatives of another crash victim took part in a memorial ceremony last May that the van Heests organized on the water near where they believe the crash happened.

Mary Fenimore, 39, of Wilmington, Del., who works in public relations for a nonprofit agency, said the crash killed her maternal grandparents, William and Rosa Freng, and her mother's sister, Barbara Freng. William Freng, whose family lived in Rye, N.Y., was vice president and chief counsel of International Telephone and Telegraph.

Fenimore said she was skeptical of van Heest's motives at first, but quickly grew to understand her intentions and appreciate her efforts.

"I'm eternally grateful for people like her who are willing to put their own time and resources in to give the rest of us a little piece of mind," she said.