The records are in such disarray that the FAA says it is worried that criminals could buy planes without the government's knowledge, or use the registration numbers of other aircraft to evade new computer systems designed to track suspicious flights. It has ordered all aircraft owners to re-register their planes in an effort to clean up its files.
About 119,000 of the aircraft on the U.S. registry have "questionable registration" because of missing forms, invalid addresses, unreported sales or other paperwork problems, according to the FAA. In many cases, the FAA cannot say who owns a plane or even whether it is still flying or has been junked.
Already there have been cases of drug traffickers using phony U.S. registration numbers, as well as instances of mistaken identity in which police raided the wrong plane because of faulty record-keeping.
Next year, the FAA will begin canceling the registration certificates of all 357,000 aircraft and require owners to register anew, a move that is causing grumbling among airlines, banks and leasing companies. Notices went out to the first batch of aircraft owners last month.
"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," said FAA spokeswoman Laura Brown.
The FAA says security isn't the only reason it needs an up-to-date registry. Regulators use it to contact owners about safety problems, states rely on it to charge sales tax and some airports employ it to bill for landing fees. Also, rescuers use the database to track down planes that are missing.
But the FAA has emphasized the security and law enforcement angle as the new measure has moved through the rule-making process over the past two years. The agency says the paperwork gap is becoming a bigger problem as authorities increasingly rely on computers to tighten aviation security in the wake of 9/11 and other terrorist plots.
There have already been cases of criminals using U.S. registration numbers, also known as N-numbers or tail numbers, to disguise their airplanes. In 2008, Venezuela authorities seized a twin-engine plane with the registration number N395CA on the fuselage and more than 1,500 pounds of cocaine on board.
Soon afterward, airplane owner Steven Lathrop of Ellensburg, Wash., received a call from a reporter.
"He sort of started the conversation with, `Do you know where your airplane is? ... Your airplane's in a jungle in South America,'" Lathrop said.
Lathrop's Piper Cheyenne II XL was locked safely in its hangar at the Ellensburg airport. The smugglers had apparently chosen his tail number because the model was similar to their plane.
"Anybody with a roll of duct tape can put any number they want on an airplane," Lathrop said.
Federal law requires all U.S. aircraft owners to register their planes with the FAA and carry the registration certificate on board. The registration number
-- all U.S. registrations start with the letter N -- is painted on the fuselage or tail. The numbers are used on flight plan forms and by air traffic controllers to communicate with aircraft in flight.
The amount of missing or invalid paperwork has been building for decades, the FAA says. Up to now, owners had to register their planes only once, at the time of purchase. The FAA sent out notices every three years asking owners to update their contact information if needed, but there was no punishment for not doing so. As of 2008, there were 343,000 airplanes on the registry. By 2010, the number had risen to 357,000.
The U.S. registry includes 16,000 aircraft that were sold but never updated with the names of the new owners, and more than 14,000 aircraft that have had their registrations revoked but may still be flying because the FAA has not canceled their N-numbers. Other registrations are outdated because the owners have died or the planes were totaled in crashes. Some planes are simply derelicts corroding in barns or junkyards.
As a result, there is a "large pool" of N-numbers "that can facilitate drug, terrorist or other illegal activities," the FAA warned in a 2007 report.
The problem became more acute after the government launched a new computer system for tracking flights called the Automatic Detection and Processing Terminal, or ADAPT, the FAA says. The system combines dozens of databases, from a list of stolen aircraft to the names of diplomats. It flags suspicious flights in red on a map.