Updated

Some air travelers are wondering how 11 people could walk through an unattended security checkpoint lane at one of the nation's busiest airports even with the enhanced security measures put in place after the Sept. 11 attacks.

The incident Monday at New York's Kennedy Airport is being investigated by the Transportation Security Administration.

At Boston's Logan International Airport — a staging point for two of the jetliners used on 9/11 — some travelers said they were surprised a checkpoint lane could be left unattended. Security procedures now include body scans, pat-downs and screening of checked luggage for explosives.

The TSA says that three passengers didn't receive required secondary screening after they set off the metal detector but that it's confident the incident presented "minimal risk to the aviation transportation system."