WASHINGTON — The Transportation Security Administration cannot determine the real identities of thousands of the people to whom the Federal Aviation Administration has issued licenses as pilots and aircraft mechanics, but has located an additional 27 who should not have held them because of terrorist connections, according to an internal report by the Department of Homeland Security.

The report was requested two years ago by four senators after a private data analysis company in New York determined that the man convicted of bombing Pan Am Flight 103 over Lockerbie, Scotland, in 1988 still held an F.A.A. license, as did a man caught trying to smuggle military equipment to Hezbollah in Lebanon, a man convicted of trying to make an airborne poison in his basement and a self-described eco-terrorist who fled the country after he was indicted on a charge of arson.