Federal investigators have begun the complicated task of finding out what caused the small-plane crash in Montgomery County early Thursday that claimed the lives of two Philadelphia-area doctors and their 19-year-old daughter.

Adam Gerhardt, an air safety investigator for the National Transportation Safety Board, said investigators are collecting pieces of the single-engine Beechcraft Bonanza F33A at the crash site in Upper Moreland for transport to a secure facility in Clayton, Del., for further study.

Staff from the federal agency will remain in Upper Moreland for the next few days, Gerhardt said. A preliminary report of their findings will be made available this month, with the full version to bereleased within a year.

The lack of eyewitnesses to the crash — neighbors only heard the sound of the descending plane — may complicate the investigation. It was not immediately known, for instance, whether the plane went straight in on its final descent or was in a glide. There was no distress call from pilot Jasvir Khurana, 60, a professor at Temple University’s Katz School of Medicine.

Khurana; his wife, Divya, 54, also a professor; and their 19-year-old daughter, Kiran, were killed. The couple’s older daughter, Saranya, was not aboard, authorities said. The family lived in Lower Merion.

Upper Moreland Police Chief S. Michael Murphy said his department was hoping to locate footage from home security cameras that might have captured some of the plane’s last moments.

After taking off from Northeast Philadelphia Airport bound for Ohio, the plane was airborne for only three minutes before rapidly losing altitude and crashing into the rear yards of four homes on Minnie Lane, about 10 miles from the airport. No one on the ground was harmed.

The Bonanza reached an altitude of 1,325 feet before heading down, picking up speed as it descended. At the last point of radar measurement, 775 feet from the ground, it was moving at 205 mph.

One neighbor, John Quatrini, said he heard what appeared to be a loud engine directly above his house just before the crash 400 yards away, suggesting that the plane’s engine was working or at least had been restarted as the plane descended.

Debris was spread over four properties. Al Yurman, a former NTSB investigator, said Friday that agency experts would study where pieces were scattered for evidence of a possible airborne structural failure.

Unlike commercial jets, private planes are not required to be equipped with a “black box” to store flight data. Some owners upgrade their private planes to include them.

The Bonanza is among the most popular single-engine planes in the United States. Beechcraft has produced 17,000 since 1947, making it the longest continually produced plane still being manufactured. Estimates are that 12,000 are still being flown.

The Khuranas’ Bonanza was built in 1975; experts say the typical private plane in the U.S. is of that v

intage. A used plane sells for between $80,000 and $300,000, experts said. Its powerful engine permits it to take off from smaller airfields, climb rapidly, and cruise at 200 mph.

In the last decade, there have been 10 fatal crashes of the plane in the U.S., killing 17 people. In several of those cases, the NTSB was unable to determine precisely what caused the crash. After one such crash, for instance, the final report blamed the accident on a "loss of airplane control for reasons that could not be determined because examination of the wreckage revealed no mechanical deficiencies. "

Tom Turner, executive director of the air safety arm of the American Bonanza Society, an organization for owners of the aircraft, said its overall safety record was excellent, given the large number of planes still in use.

Tom Haines, a spokesman for the Aircraft Owners and Pilots Association, the national organization for private-plane owners, agreed, saying the craft had “a very good safety record.”

In general, he said, the accident rates for private planes has fallen in half in the last 20 years. When crashes do happen, he said, the cause is most often pilot error.

He said the high-performance piston-engine Bonanza with retractable landing gear was a high-status buy, “the kind of plane that people look forward to owning when they reach a certain point in life.”

Stephanie Harder, spokesman for Textron Aviation Inc., maker of Beechcraft, declined Friday to discuss the accident or any matters involving the plane. Textron, which manufactured Cessna planes, acquired Beechcraft in 2014 in a major consolidation in the private-airplane industry. Both firms are based in Wichita, Kan.

Jasvir Khurana, who was first licensed as a pilot five years ago, was a professor of pathology and laboratory medicine at Temple. His wife was a pediatric neurologist at St. Christopher’s Hospital for Children and a professor at Drexel University College of Medicine.

Kiran Khurana graduated last year from Harriton High School, where she was on a nationally ranked squash team. After leaving Harriton, she enrolled at McGill University in Montreal.

Those who knew the Khuranas continued to grieve Friday.

Larry Kaiser, dean of the Katz School of Medicine, recalled Jasvir Khurana as a quiet and personable man who “always had a smile.”

Kaiser said he first met Khurana more than 20 years ago, when both were at Penn Medicine.

Khurana joined Temple’s pathology department in 2002 and specialized in bone diseases. With 32 clinical and research faculty members, the pathology department is relatively small, and professors work closely with residents.

Khurana took pride in his role as an educator, Kaiser said.

“He made a major contribution to a generation of students and residents. That’s really what all of us are in this business for,” Kaiser said Friday as dozens of Temple medical students and their families buzzed around him following a white-coat ceremony for 195 students at the university’s performing arts center.

The nature of Khurana’s death has shaken the Temple community, Kaiser said. “The suddenness makes it all that much more difficult, especially in a department like pathology where it’s one-on-one-type mentoring and teaching,” he said.

The death hit hard, too, at Harriton. Tom O’Brien, a longtime staffer there, said Khuranas had been fixtures at the school for more than a decade — among Kiran, her older sister, and three cousins, at least one member of the family has walked the school’s halls since 2008.

“This is absolutely devastating,” said O’Brien, coordinator of the school’s International Baccalaureate program, which the Khurana girls were actively involved in and for which their parents volunteered.

“Just so much lost potential,” he added. “Kiran, at 19, had her entire future ahead of her.”

“She was just a sweet, quiet, lovely young woman. Just a really lovely young woman," said Neill Hartley, who directed Kiran in several shows at Harriton High.

Kiran was an ensemble member in Women on the Verge of a Nervous Breakdown in 2017, and worked on the crew in several other shows.

She had also volunteered at the Philadelphia Zoo and was one of four high school students selected to travel to Ecuador to study alongside scientists caring for critically endangered frogs.

“An extremely gifted and exceptional young woman, Kiran held a deep passion for conservation and the law, and planned to use the two to help wildlife and wild places,” said Vikram H. Dewan, zoo president. “Kiran made an indelible mark on everyone she encountered at the zoo, especially her zoo family.”

At the high school, O’Brien remembered her as reserved in contrast to her more outgoing sister. But Kiran’s quiet exterior hid a compassionate heart, he said. She cared deeply for her friends, and was always willing to assist her classmates in the program. And in the rare moments when she did speak her mind, she commanded attention.

“Certainly her teachers are upset — the range of reaction was from absolute shock to tears,” O’Brien said. “There is a lot of pain and sympathy being felt for Saranya right now.”

Staff writers Katie Park and Oona Goodin-Smith contributed to this article.