He became the first Israeli to take such a route to enter Syria's civil war, with his plans apparently unknown to his family and authorities, who minutes later scrambled military helicopters.
His fate had been a mystery, but in an interview with AFP his family confirmed they have received multiple messages from him, including a photo apparently showing him with two other jihadists.
His trip sparked an investigation in Israel, where authorities have since arrested six others suspected of seeking to join IS.
A DARING PLAN
For his family, Salah's fate was sealed nearly a year earlier, in November 2014, the day another man, Jihad Hijala, walked out of prison.
Hijala had been in Syria, allegedly with an Al-Qaeda affiliate, but returned to Israel and was jailed for six months.
After he was released, he returned to his hometown of Jaljulia north of Tel Aviv, where the Salahs also live. Hijala is accused of quickly setting about establishing a jihadist cell that would eventually travel to Syria.
Among those he recruited was Salah, who fell under the spell of the man three years his senior, his family said. The Salahs are Muslim but the family are not particularly devout.
Salah began going to his mosque five times a day and would only talk about religion.
"His personality changed," said his brother Samih, who shared a bedroom with him until recently.
"He banned listening to music, and would only listen to (recordings of) the Koran."
Salah's uncle Rifaat accused the Israeli security agency Shin Bet of failing to monitor Hijala's activities.
"If Israel wanted to stop him, they could have stopped him," he said.
In total seven people from the small town would meet at Hijala's house, including two of his brothers, and discuss plans to travel to Syria, Shin Bet said.
The other six have since been arrested on charges of aiming to join IS.
SMILING BUT BANDAGED
Knowing he could not travel through an Israeli airport, Hijala allegedly proposed he and Salah paraglide over the border.
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Such engine-powered gliders typically need several months' training to operate safely, said Ofer Rockenstein, one of Israel's most experienced paragliders.
Salah's family confirmed the two men had been training nearby, explaining they didn't think it was unusual as Salah was into sports.
Then on October 24, Salah allegedly travelled to the border.
From the field where he launched, Salah would have been able to see Jamlah a few kilometres (miles) away, the small Syrian town under the control of the IS-affiliated Al-Yarmuk Martyrs Brigade.
The journey would have taken only about 15 minutes, Rockenstein said.
Only a tiny fraction of Israel's estimated 1.4 million Arab Israelis are believed to have any sympathy with IS, with around 50 estimated to have gone to Syria since the conflict broke out in 2011.
The vast majority have travelled to Turkey and then crossed the porous border into northern Syria.
Salah's flight set off panic among Israeli security forces, who feared he was a paraglider accidentally swept over the border by changing winds.
Residents of a nearby Jewish settlement said the area was put on lockdown for several hours, with dozens of helicopters and military vehicles streaming to the border.
Two security force members near the frontier confirmed to AFP that a rescue plan was being developed before intelligence was received making clear the journey was not an accident.
For more than a week and a half, the family said, they heard nothing.
Then Samih received a text from an unknown number simply saying "Peace be upon you".
He saved the number in a messaging app and a photo of three bearded people emerged. Enlarging it, he saw his brother's face on the right, smiling but with a bandaged left arm.
They receive occasional updates and voice recordings, Samih said, though never with specific details.
He said he believed his brother wants to return but will not admit it.
"I know my brother -- when he is sad I know he is sad, when he is happy, I know. He sounded so sad," he said.
"I think he wants to return but there are people talking with him telling him what to tell us."
Even if he did want to return, the border between the two states is closed.
"I just want my son back," his mother says, head bowed.