"When the C.I.A. is given a task, it's usually because national policy makers don't want 'U.S. government' written all over it," said Jim Glerum, a retired C.I.A. officer who spent 18 years with the agency's Air America but says he has no knowledge of current operations. "If you're flying an executive jet into somewhere where there are plenty of executive jets, you can look like any other company."

Some of the C.I.A. planes have been used for carrying out renditions, the legal term for the agency's practice of seizing terrorism suspects in one foreign country and delivering them to be detained in another, including countries that routinely engage in torture. The resulting controversy has breached the secrecy of the agency's flights in the last two years, as plane-spotting hobbyists, activists and journalists in a dozen countries have tracked the mysterious planes' movements.

Inquiries from Abroad

The authorities in Italy and Sweden have opened investigations into the C.I.A.'s alleged role in the seizure of suspects in those countries who were then flown to Egypt for interrogation. According to Dr. Georg Nolte, a law professor at the University of Munich, under international law, nations are obligated to investigate any substantiated human rights violations committed on their territory or using their airspace.

Dr. Nolte examined the case of Khaled el-Masri, a German citizen who American officials have confirmed was pulled from a bus on the Serbia-Macedonia border on Dec. 31, 2003, and held for three weeks. Then he was drugged and beaten, by his account, before being flown to Afghanistan.

The episode illustrates the circumstantial nature of the evidence on C.I.A. flights, which often coincide with the arrest and transporting of Al Qaeda suspects. No public record states how Mr. Masri was taken to Afghanistan. But flight data shows a Boeing Business Jet operated by Aero Contractors and owned by Premier Executive Transport Services, one of the C.I.A.-linked shell companies, flew from Skopje, Macedonia, to Baghdad and on to Kabul on Jan. 24, 2004, the day after Mr. Masri's passport was marked with a Macedonian exit stamp.

Mr. Masri was later released by order of Condoleezza Rice, the national security adviser at the time, after his arrest was shown to be a case of mistaken identity.

A C.I.A. spokeswoman declined to comment for this article. Representatives of Aero Contractors, Tepper Aviation and Pegasus Technologies, which operate the agency planes, said they could not discuss their clients' identities. "We've been doing business with the government for a long time, and one of the reasons is, we don't talk about it," said Robert W. Blowers, Aero's assistant manager.

A Varied Fleet

But records filed with the Federal Aviation Administration provide a detailed, if incomplete, portrait of the agency's aviation wing.

The fleet includes a World War II-era DC-3 and a sleek Gulfstream V executive jet, as well as workhorse Hercules transport planes and Spanish-built aircraft that can drop into tight airstrips. The flagship is the Boeing Business Jet, based on the 737 model, which Aero flies from Kinston, N.C., because the runway at Johnston County is too short for it.

Most of the shell companies that are the planes' nominal owners hold permits to land at American military bases worldwide, a clue to their global mission. Flight records show that at least 11 of the aircraft have landed at Camp Peary, the Virginia base where the C.I.A. operates its training facility, known as "the Farm." Several planes have also made regular trips to Guantánamo.

But the facility that turns up most often in records of the 26 planes is little Johnston County Airport, which mainly serves private pilots and a few local corporations. At one end of the 5,500-foot runway are the modest airport offices, a flight school and fuel tanks. At the other end are the hangars and offices of Aero Contractors, down a tree-lined driveway named for Charlie Day, an airplane mechanic who earned a reputation as an engine magician working on secret operations in Laos during the Vietnam War.

"To tell you the truth, I don't know what they do," said Ray Blackmon, the airport manager, noting that Aero has its own mechanics and fuel tanks, keeping nosey outsiders away. But he called the Aero workers "good neighbors," always ready to lend a tool.

Son of Air America

Aero appears to be the direct descendant of Air America, a C.I.A.-operated air "proprietary," as agency-controlled companies are called.

Just three years after the big Asian air company was closed in 1976, one of its chief pilots, Jim Rhyne, was asked to open a new air company, according to a former Aero Contractors employee whose account is supported by corporate records.

"Jim is one of the great untold stories of heroic work for the U.S. government," said Bill Leary, a professor emeritus of history at the University of Georgia who has written about the C.I.A.'s air operations. Mr. Rhyne had a prosthetic leg - he had lost one leg to enemy antiaircraft fire in Laos - that was blamed for his death in a 2001 crash while testing a friend's new plane at Johnston County Airport.

Mr. Rhyne had chosen the rural airfield in part because it was handy to Fort Bragg and many Special Forces veterans, and in part because it had no tower from which Aero's operations could be spied on, a former pilot said.

"Sometimes a plane would go in the hangar with one tail number and come out in the middle of the night with another," said the former pilot. He asked not to be identified because when he was hired, after responding to a newspaper advertisement seeking pilots for the C.I.A., he signed a secrecy agreement.

While flying for Aero in the 1980's and 1990's, the pilot said, he ferried King Hussein, Jordan's late ruler, around the United States; kept American-backed rebels like Jonas Savimbi of Angola supplied with guns and food; hopped across the jungles of Colombia to fight the drug trade; and retrieved shoulder-fired Stinger missiles and other weapons from former Soviet republics in Central Asia.