In 2009, authorities in the west African country of Mali discovered a 1978 Boeing 727 that had recently burned in an isolated region of the country’s northern desert. The aircraft landed there after taking off from Venezuela, intelligence sources later reported, loaded with nine tons of cocaine. According to the U.S. Drug Enforcement Administration, the wholesale value of the cargo was $225 million. Law enforcement officers believe the cocaine was taken north from Mali and eventually smuggled into Europe.

Just two years earlier, that 727 had been the property of Finova Capital, a finance company in Scottsdale, Arizona. Finova sold it in 2007 to a Spain-based subsidiary of West African Aviation. In the two years between its sale and its destruction, the aircraft was owned by three entities in four countries and assigned three different registrations. Its last airworthiness certificate, granted by the Saudi Arabian General Authority of Civil Aviation, had expired. Investigators determined that the airplane had been torched by the crew, but no crew member has been found.

The “Mali drugplane,” as the 727 became known, is a “ghost plane”: a term United Nations investigators use for aircraft with false registration numbers, lapsed certificates of airworthiness, or missing or incorrect manufacturing numbers, and usually with long, byzantine histories of ownership or leasing—in other words, airplanes that are very difficult or impossible to trace. One day an aircraft is flying for a charter service, delivering humanitarian relief cargo for an NGO or hauling freight to a mine; the next day it is gone, never to be seen again, or, like the Mali drugplane, reemerging in some nefarious operation.

I became intrigued (some of my friends say “obsessed”) with the search for a ghost plane in 2010, when I wrote about Boeing 727 N844AA, which took off one day from Luanda, Angola, and has not been seen since (see “The 727 That Vanished,” Sept. 2010). When I started research for the article, I thought the case of N844AA was extraordinary, perhaps unique. Since then, I’ve learned that there are hundreds of ghost planes, most of them spirited out of Russia after the 1991 dissolution of the Soviet Union. What is more shocking—and potentially more dangerous—is that the vanished airplanes include almost 50 large U.S. transports: 11 Boeing 737s and 26 707s and 727s; two Douglas DC‑8s and two DC-9s; two Lockheed L100s (the civilian variant of the C-130); and one C-130.

To the U.S. security analysts, government officials, and airline business professionals I’ve interviewed, these missing airplanes are a security threat. “Any aircraft that is not accounted for represents a concern because of the unique capability of aircraft to bound over the top of terrestrial defenses, go beyond ports, and be able to penetrate directly into large continental spaces,” says a former government employee who requested anonymity. “Timothy McVeigh [the Oklahoma City bomber] showed us what can be done with a Ryder truck. And that was just a truck. I know what [terrorists] can do if they put their minds to it.”

Because missing airplanes exist in a world of criminal investigations and classified information, almost no one who is knowledgeable about them will discuss the problem on the record. Many say that they “don’t want the bad guys to know what we know.” Some want to protect their security clearances or their jobs within the intelligence services and commercial aviation; others are fearful of retaliation by criminals they know to be involved with the aircraft. Kip Hawley, director of the U.S. Transportation Security Administration from 2005 to 2009, was one of the few who agreed to be quoted.

“We’re pretty well protected against somebody with a stolen airframe that is flying around, entering our airspace, that is not identified properly and headed to crash into a building,” says Hawley. “There is a well developed and not all secret [plan]. If there are planes in U.S. airspace, it’s very simple to shoot [them] down. It’s not something that’s done lightly, [but] the system is greased, it’s rehearsed. And they literally have open phone lines 24 by 7.

“The one that I most worried about was if al-Qaeda were to get access to a nuclear weapon,” he says. “[They] wouldn’t dump it into a shipping container and let it float across one of the oceans for three weeks. They would put it into an airplane and call it a freighter or call it something else and then fly it to its destination and of course never land. It was in those scenarios that we were most interested in missing aircraft.”

Are missing aircraft more likely to be involved in a terrorist attack than a legitimately recognized airliner or cargo aircraft? “It’s hard to say,” says a former member of the intelligence community. “The folks we’re talking about here are very patient. They could make use of an airliner that has been acquired by theft. But they could also hijack an airliner, or…. Take the case of Osama bin Laden, who was connected to a father who had so much money. Just buy an Airbus, buy a Boeing. Pick your model. Legitimately license it and go fly off in it and do something bad with it.

“The thing about missing aircraft is that they are an uncontrollable unknown. You can put security measures in place to counter a hijacker, and you can put security measures in place to do a background check on somebody buying a large aircraft, but the missing airplane is in the realm of ‘You don’t know what you don’t know.’ They’re a wild card.”

Ghost planes were sufficiently troubling to U.S. security services that in 2003, in the early stages of the N844AA investigation, President George W. Bush was given daily briefings on the case. N844AA had been converted from a passenger airliner to a freighter, and ten 500-gallon tanks had been installed in the cabin so the aircraft could haul diesel fuel to Angolan diamond mines. The realization that a flying gas tank had gone missing, just two years after the 9/11 attacks, electrified the intelligence community.

By 2007, the U.S. Air Force had in place a program called SUDDEN SPIRIT to analyze information about civilian aircraft. It was highly classified, as is the intelligence agency it spawned. According to Air Force spokesperson Major Mary Danner-Jones, “The people and mission formerly assigned to SUDDEN SPIRIT now function as the Civil Aviation Intelligence Analysis Center,” a program established in July 2011. I was not allowed to interview anyone within the CAIAC. When I asked what the employees do, Danner-Jones sent a statement: They “conduct…analysis that enables monitoring of foreign civil aviation assets involved in terrorism, weapons proliferation, and [Weapons of Mass Destruction] trafficking.” How many people work for the CAIAC? Classified. Are any of them looking for ghost aircraft? Classified. Are they trying to find out who operates them? “For obvious reasons, we don’t discuss the specifics of how we conduct intelligence.” There is no information to suggest that the CAIAC has field agents looking for ghosts. From the website of a software company that counts the CAIAC among its customers, Intelligent Software Solutions, I deduce that the agency analyzes data. ISS “provides the CAIAC with analytical tools and experienced all-source Intelligence Analysts to perform in-depth research and production of timely strategic analysis.” A slogan from another software company that supported SUDDEN SPIRIT: “We connect the dots you didn’t know were there.”

A former intelligence officer who requested anonymity believes his previous colleagues aren’t paying enough attention to missing airplanes. “The government has all this freaking expensive stuff—satellites and gadgets and shadowy operations—that collect all this secretive information. Almost none of it is focused on civil aviation. They’re focused on the same crap they’ve been focused on forever, which is foreign military capabilities. If you want to know about some foreign fighter jet, there are probably thousands of people focused on that. If you want to know [about] an airliner, there might be one guy in the whole government.”

The people who know what’s happening in civilian aviation, he adds, “are people in the private sector in the aviation industry.”

That would be Alexandre Avrane, for one, creator of the online catalog AeroTransport Data Bank. When used-aircraft brokers, UN investigators, aid organizations, journalists, or intelligence agencies want information about aircraft capable of carrying 30 passengers or more (or the equivalent tonnage in freight), they often turn to Avrane’s database, which currently has more than 1,000 subscribers and holds records for 81,554 aircraft. Avrane, who lives in Paris, has been adding to the database since 1997. He and his staff rely heavily on computerized aircraft tracking technologies, aviation websites and publications, and a worldwide network of informants, but their greatest tool is probably Avrane’s passion.