The White House was placed on lockdown for approximately 30 minutes on Tuesday, as fighters scrambled from a nearby air base to intercept a small aircraft or something that penetrated the restricted airspace around the President’s home. Roads in the area were closed and a number of buildings were evacuated as a precaution.

“Senior officials across the interagency are monitoring the situation on a national event conference call. NORAD aircraft are on site and responding,” Lt. Col. Chris Mitchell, a Pentagon spokesman, said.

According to reports from D.C., the U.S. Capitol Police scrambled at least one helicopter to support air intercept fighters that departed from Joint Base Andrews shortly after 8:30 a.m. Washington D.C. time.

Initial reports indicated that a small aircraft was being tracked moving east into White House’s restricted airspace, but subsequent statements have brought that assertion into question. One official told Fox News that their radar was showing “different sectors” as to where the threat was coming from. Another official said that whatever prompted the lockdown was an “anomaly,” he further guessed that it might have been geese.

“The White House was locked down this morning due to a potential violation of the restricted airspace in the National Capital Region,” a Secret Service spokesman told reporters in a statement. “The lockdown has been lifted at this time.”

The entire incident was over about 45 minutes after it started, suggesting that whatever it was that operators spotted on their radar screens was quickly assessed as either not physically there or no threat to the president or his staff. A flock of geese would certainly qualify, though it seems unusual that the advanced air defenses around Washington D.C. would find themselves so fooled by what is likely a common occurrence. With a great deal of civilian air traffic in and around the nation’s capital, it also stands to reason that the alert may have been spurred by a wayward pilot in a small aircraft like a Cessna 172 that mistakenly drifted into the restricted area.

Of course, if it wasn’t a flock of geese or a wayward pilot, this wouldn’t be the first time the White House is visited by an unidentified aircraft. Back in July of 1952, while (it’s important to note) America was gripped by both the pop-culture phenomenon of “flying saucers” and a growing concern for Soviet aggression, a series of unusual blips appeared on the radar screens of Washington National Airport. Radar at two nearby military installations, Andrews Air Force Base and Bolling Air Force Base, both tracked the same objects and scrambled Air Force F-94 fighters to intercept. After the fighters turned up empty handed, a similar event took place again just a few days later.

Washington D.C. has maintained an Air Defense Identification Zone (ADIZ) around the Baltimore-Washington Metropolitan Area since 2003 specifically for the purposes of restricting air traffic near the nation’s capital. Despite broad efforts to notify pilots of this zone, it is still not uncommon for some to mistakenly violate it. However, despite common violations of the ADIZ, it is exceedingly uncommon for a threat to push the White House into going on lockdown, which begs some questions about what exactly it was that operators saw on their scopes on Tuesday morning. But until officials offer more details, it may be safer to assume it was a Cessna, rather than ET.