PHILADELPHIA By cleaning up the grounds and creek at Pennypack Park on Saturday, Christopher Alvelo had completed the final project needed in his pursuit of the prestigious Eagle Scout rank, his family said.

The 17-year-old senior at New Foundations Charter School and three friends were looking forward to a future banquet celebrating their scouting accomplishment as they left the park Saturday afternoon.

They were on their way home to Northeast Philadelphia in a 2007 Ford Explorer driven by Alvelo's stepfather, Joseph Snyder, when the 51-year-old fell unconscious. Alvelo, who was in the front passenger seat, unbuckled his seat belt and tried to take control of the steering wheel as the SUV veered off the road.

"He saw his father was going to be in trouble, and he wanted to prevent the accident," said Alvelo's aunt and godmother, Susan Foremski.

Tragically, the SUV crashed into a parked, unoccupied Chevrolet paratransit vehicle near Northeast Airport. Alvelo was killed instantly in the impact.

"It's such a tragedy, but he is a hero," Foremski said Sunday.

If Alvelo had not turned the Explorer as he had, the SUV would have crashed into a tank full of heating oil, his aunt said. "He saved four people, basically," she said.

Snyder, who suffered a broken back, broken leg, and fractured arm in the accident, was in stable but critical condition at Aria Health-Torresdale Campus on Sunday, Foremski said. The three backseat passengers - Alvelo's fellow scouts, all 15 - were being treated for minor injuries at St. Christopher's Hospital for Children, police said.

"It's awful because Joe feels it was his fault, and it wasn't," Foremski said.

Doctors had not determined why Snyder passed out, Foremski said.

Alvelo would have turned 18 in December. He had plans to join the Air Force next year after graduating from high school, his aunt said.

"He was just a kindred soul. He was just a kind, kind spirit, a kind person," Foremski said. "He was not rude. He was not disrespectful. He was a one-in-a-million 17-year-old kid. You don't meet too many 17-year-olds who hold the door for you. . . . He was a good, good kid."

Alvelo's friends and classmates turned to Twitter over the weekend to express their grief.

A vigil is planned for 7 p.m. Monday at the New Foundations parking lot at Torresdale Avenue and Rhawn Street.