Julio Alberto Poch is accused of illegal detentions, tortures, disappearances and deaths when he served as a military pilot during the 1976-1983 junta, which killed as many as 30,000 people.
Poch arrived in Buenos Aires Thursday and faces a court hearing Friday. He has denied the charges.
Poch, 57, was turned in by his own co-workers at the Dutch airline where he worked after the dictatorship. They said he had bragged about the death flights and was unrepentant about executing people he considered to be terrorists.
About 1,000 people are believed to have been drugged, tied up and thrown alive into the sea from military planes after being kidnapped and tortured inside Argentina's Navy Mechanics School. Poch is accused of piloting the planes used to dispose of journalist Rodolfo Walsh and the French nuns Alice Domon and Leonie Duquet, among others.
Argentina had asked the Netherlands for his extradition, but the request was complicated by the Dutch citizenship Poch had obtained. Finally, Spain acted on Argentina's request, arresting him in front of his passengers and family during a stop in Valencia on what was supposed to be his final flight back to the Netherlands before retiring from Transavia, a subsidiary of KLM-Air France.
Also awaiting a hearing Thursday was Jose Alfredo Martinez de Hoz, the powerful economy minister who ran Argentina's finances during most of the dictatorship. Now 84, he was arrested Tuesday and his bank accounts were frozen. He is being detained in a private clinic due to his poor health.
Martinez de Hoz is charged along with former dictator Rafael Videla with the kidnapping and extortion of two executives of a cotton export business in 1976. According to court records, Federico and Miguel Ernesto Gutheim were held for five months, and set free only after giving up control of their company to a firm approved by economy ministry. They fled into exile and never returned.
Martinez de Hoz was economy minister from 1976-1981, one of the few civilians to hold a high position with the military junta. Some wealthy and well-connected Argentines prospered under his tenure, but many others descended into poverty as the country's external debt quadrupled and government spending was cut sharply.