From Seattle Times:

It's bad enough when an airline loses one of your bags. But when it can't find your father?
An Edmonds man knows the feeling.
Eugene Shchytou said Wednesday he went to Seattle-Tacoma International Airport on Tuesday night to pick up his father, 59-year-old Evgeny, of Belarus, who was on his way to Seattle via New York.
After other passengers on Delta Air Lines Flight 1643 had arrived and claimed their bags, Shchytou began to worry. He and his wife had been standing above the escalators to the baggage area, but couldn't see him.
They found the father's bag, and approached a Delta official.
"I asked them to check whether he was on the plane," Shchytou said.
The Delta representative said he was.
Shchytou then asked if there had been any reports of a lost or wandering person in the terminal.
Delta said there weren't, but airline representatives contacted airport police, who took down a description of the elder Shchytou. They paged him, but the father doesn't speak English.
The elder Shchytou's journey started Tuesday morning in Minsk, the capital of Belarus, which is 10 hours ahead of Seattle time. He took a flight to Milan, Italy, his son said. There he boarded a Delta flight to New York, where he went through immigration. From New York, he was to board the Delta flight to Seattle, arriving at 10:42 p.m. Tuesday.
The son called JFK airport in New York and asked if there was a missing or detained person who fit his father's description. The airport checked with police and medical offices, but, no, there wasn't.
A minute later, his mother called from Belarus — his father had indeed arrived in New York, but instead of boarding the flight to Seattle he somehow got on a plane to Frankfurt, Germany. Evgeny Sr. managed to find a Russian-speaking person who helped him, through Delta representatives, get back on a (no-cost) flight to the U.S.
Shchytou said German airport representatives and police officials "were very mad about the fact that the Americans just allowed a random person on a plane to Germany, and they were regarding this as a major safety and security breach."
"You would think that 10 years after 9/11, this couldn't happen," Shchytou said.
Despite his safety concerns, Shchytou was ultimately pleased with Delta's help.
Delta representative Susan Elliott said Evgeny Shchytou was quickly put on a return flight and put in touch with his family. Delta said it is investigating, but that there was no security breach.
The elder Shchytou was taking it all in stride, despite the long flight back to the U.S.
The father arrived at Sea-Tac early Wednesday evening, after nearly three days of traveling.
"He's pretty happy," his son said. "He is in good spirits. He's happy to lie down."

Local News | Delta put dad on wrong flight | Seattle Times Newspaper