74-year-old Jacques Wilmart, suffered heart problems on Thursday and was taken to the French military base in N'Djamena for treatment, his lawyer said.
After disembarking from a Spanish air force plane in the Spanish capital, Agustin Rey, a pilot for Catalan air charter company Girjet, thanked the government and the public for their support.
"We stayed a crew at all times, and I'm really proud of each and every one of them," Rey said, as fellow crew members Daniel Gonzalez and Sergio Munoz stood alongside him.
"The first moments were very difficult, we were uncertain of what was happening," he said, referring to their arrest on October 25.
Mother speaks out
Spanish media reported the releases followed testimony given by the detained leader of the Zoe's Ark group, Eric Breteau, who said the released Europeans were not involved in the group's activities in Chad.
Chad says the group did not have permission to take the children out of the country.
|Three Spanish flight crew arrived back in Madrid|
after being freed by Chadian authorities [AFP]
Ayash Fadl, the mother of two children allegedly involved in the case, told Al Jazeera: "I was told that my children would be taken to another town only to learn Arabic and study the Koran. I could visit them every week."
"I wasn't told they would be taken to another place."
The French organisation has said the children were orphans from Sudan's Darfur region and it had hoped to fly them to safety to Europe for foster care with families there.
However, United Nations officials say almost all of the children came from villages on the Chad-Sudan border and had at least one living parent.
The Spanish crew were the second group of Europeans from the original 17, who were detained in late October in eastern Chad close to the border with Darfur, to be freed.
On Sunday four Spanish female flight attendants and three French journalists were released by Chad and flown back to Europe with Nicolas Sarkozy, the French president.
He had travelled to Chad to discuss the case with Idriss Derby, his counterpart.
On Friday, the Chadian government said it was to investigate reports that at least 74 more children were flown to France in September without their parents' knowledge, a senior judicial official said.