Spy craft, or just another private jet at Napa County Airport?

That question arose after a Gulfstream jet with a notorious tail number flew in and out of the airport last week.

The plane’s tail number, N1HC, is mentioned in a European Parliament document from 2006 that describes planes chartered by the Central Intelligence Agency. The CIA reportedly used a plane with that tail number, among other craft, to transport terrorist suspects to secret locations overseas, where the suspects were subjected to extreme interrogation techniques in an effort to gain information about terrorist networks.

The so-called “extraordinary renditions” to other countries have been a source of controversy for the Bush administration, which has defended the practice as a powerful way to gain information about terrorist networks.

According to the European Parliament document, “The N1HC is listed as an alleged CIA airplane, according to the report of the Scottish National Party.”

The document also states a plane bearing the same tail number flew several rendition missions out of various cities in eastern and western Europe in recent years.

A Central Intelligence Agency spokesman declined to answer questions on the N1HC or on whether the CIA receives similar queries.

“While the CIA does not, as a rule, comment on specific cases or allegations — in spite of all the myth and misinformation — renditions are a key, lawful tool in the fight against terror and have helped the United States and other countries disrupt terrorist plots and networks,” CIA spokesman George Little wrote in an e-mail.

The plane, registered to a private charter company in Oklahoma, flew from Indianapolis to Napa on Aug. 6 and returned to Indianapolis on Friday, according to FlightAware, a Web site that tracks flights.

Such a flight path suggests a routine corporate visit to the Napa Valley rather than a mission linked to the war on terror.

Shortly before departing, one of the plane’s pilots declined to comment as he stood near the front counter at Bridgeford Flying Services, the company that services planes at the airport.

A woman who answered the phone at United States Aviation Co., the Oklahoma-based company the Federal Aviation Administration lists as the owner of the plane, declined to say who chartered the plane.

Workers approached at Napa County Airport last week either did not know or would not disclose information on the Gulfstream parked a few hundred feet from the public parking lot.

Harold Morrison, president of Bridgeford Flying Services, said the company does not disclose the identity of those who fly in and out of the airport, in order to protect the clients’ privacy and to ensure their safety. They can be heads of industry or celebrities who do not want their movements known, he said.

Gulfstreams like the plane in question are fairly common at the airport, Morrison said.

Bill Tuthill, the owner of Jonesy’s, the restaurant at the airport, said he had not noticed the airplane. But then again, celebrities and political figures have flown into and out of the airport without notice.

“I don’t pay too much attention,” said Tuthill, who said dignitaries and celebrities like Kurt Russell are left alone when they come to eat at his restaurant.

Airport Manager Martin Pehl also said he had no idea who flew in that airplane. He referred the question to the Federal Aviation Administration.

FAA spokesman Ian Gregor confirmed the plane was registered in 2003 to United States Aviation Co. The tail number was previously registered to the Gulfstream Aerospace Corp., the company that builds the aircraft.

Tail numbers can be recycled if the plane crashes or is scrapped, Gregor explained. On Wednesday, he said it did not appear that the N1HC was a recycled tail number.