The Federal Aviation Administration said it is missing registration records for one-third of the private and commercial aircraft in the United States, identifying a security gap which the agency fears, could be exploited.
The FAA said it is concerned that terrorists or drug traffickers could purchase planes, or use the registration numbers of other aircraft without the government's knowledge, in order to evade computer tracking systems intended to identify suspicious flights.
"There are so many opportunities for either hijacking, renting or owning an aircraft that could be used to fly into a chemical plant, or a nuclear facility or an iconic building," former 9/11 Commission member Richard Ben-Veniste said.
About 119,000 of the 357,000 aircraft in the U.S. registry have "questionable registration," according to the FAA, because of paperwork problems including invalid addresses or missing forms.
FAA spokesperson Laura Brown told ABC News the agency sends out cards every three years to small airplane owners, asking them to update contact information. In many cases, the cards are not returned or come back to the FAA undeliverable because the owner of the aircraft has moved to a different address or died.
Currently, even if the card is not returned, the FAA does not revoke the aircraft registration, or take any action, she said.
"How can we revoke the registration if we can't even reach the owner?" Brown asked. She said the agency does not revoke the aircraft's one-of-a-kind tail number registration because it runs the risk of reissuing the number and ending up with duplicate numbers on active aircraft.
As of 2010, the U.S. registry includes 16,000 aircraft that were sold but never updated with the names of new owners, and more than 14,000 aircraft that have had their registrations revoked, but may still be in the air because the FAA has not canceled their identification numbers, also known as N-numbers.
This information gap leaves a "large pool" of N-numbers "that can facilitate drug, terrorist or other illegal activities," the FAA cautioned in a 2007 report.
The FAA issued a press release in July announcing the agency had finalized recurrent aircraft registration rules in order to create a more accurate registration database and improve security. The regulations would require re-registration of all civil aircraft over the next three years and renewal every three years after that.
"These improvements will give us more up-to-date registration data and better information about the state of the aviation industry," FAA Administrator Randy Babbitt said in the release.
Ben-Veniste said he's happy the FAA is "starting to do something, even at this late date."
"Civil aviation is an area that needs to be addressed in a better way," he said. But for Ben-Veniste, plane ownership is only one part of the equation for secure civil aviation.
"People can rent a plane, people can overpower a pilot," he said. "There are all kinds of permutations that lead to a terrible result."
Heightened Concern About Registration GapCurrent regulations require aircraft owners to report the sale or destruction of planes, as well as changes in mailing addresses. The July release indicated many owners have not complied with FAA requirements, and said the organization would cancel the N-numbers of aircraft that are not re-registered or renewed by their expiration date.
Brown said, "We have identified some potential risk areas, but I think we're trying to eliminate as much risk as possible through the re-registration process." Last month, notices went out to the first batch of owners whose registrations are set to expire.
She said the rule change will help track ownership transfers, many of which she said are not "deliberate deception."
For example, she said, "If a father dies, and his son takes ownership of the plane and moves it to his home, we have no way of knowing."
Though agency regulators use registration information to contact owners about safety problems, the FAA's emphasis has been on law enforcement and security in pushing for the new regulations over the past two years. The gap in registrations has become a bigger concern for authorities, following the 9/11 attacks, and more recent plots involving terror threats against aircraft.
Federal law stipulates all U.S. aircraft owners must register their planes with the FAA and carry the registration certificate onboard. The registration number, which begins with the letter N, is painted on the fuselage or tail of the aircraft and is used by air traffic controllers to communicate with aircraft in flight.
The Associated Press contributed to this report.