Little was clear Tuesday morning in Washington when authorities locked down access to both the White House and the U.S. Capitol.

But it was clear to me what was probably unfolding: an aircraft had likely punctured the bubble of restricted airspace protecting Washington, D.C.

I’ve been through dozens of these drills on Capitol Hill since 9/11. If you’ve been at this for as long as I have, you can usually divine what sort of security threat is afoot at the Capitol and how serious it may be. Some of it is “feel.” Some of it is observation. Some of it is the way authorities respond.

LOCKDOWN LIFTED AFTER APPARENT AIRSPACE VIOLATION CAUSES DC SCARE

I wasn’t in Washington on Tuesday morning. I was in Nashville for a wedding. I had just concluded a jog around Music City's version of "Capitol Hill" and the Tennessee state capital grounds word filtered through that there was a problem in D.C. A “universal” alert for both the White House and the Capitol usually indicates some sort of an incursion by air. But dozens of Congressional sources confided there were serious problems with alerting those who work on Capitol Hill, saying the response was “uneven” at best.

One source on Capitol Hill even likened U.S. Capitol Police's handling of things to “Animal Farm": Some people appeared to be “a little safer” than others.

Several sources who work on Capitol Hill tell Fox they were warned that the Capitol complex and the surrounding buildings were “closed” and that no one could enter. Other sources who had already arrived for work were advised to shelter in place, lock the doors to their offices and remain inside.

Fox is told some officers told those emerging from the Capitol South Metro Station just behind the Cannon House Office Building to head south. That’s good advice if a plane is coming in and they’re worried about people being near the Capitol. But it doesn’t do much good for people who weren’t alerted at all and were already inside the buildings.

OFFICIALS STILL PUZZLED ABOUT 'HOVERING OBJECT' THAT PROMPTED LOCKDOWN IN DC

“No good,” said one source. “This is a life and death situation.”

Most appallingly, no one who works on Capitol Hill ever got any sort of electronic alert or alarm that anything was going on at all. Such alerts and advisories happen constantly if you work on Capitol Hill: Street closures due to protests or a malfunctioning road barricade. A suspicious package in the Hart Senate Office Building. On Monday, U.S. Capitol Police (USCP) issued an advisory regarding a “training exercise.”

“Small groups of USCP officers may be seen running to multiple locations and maintaining tactical formation. Again, this is only a training exercise,” announced a USCP advisory Monday night.

It’s remarkable how many alerts go out about forgotten backpacks. Yet on Tuesday… nothing.

Authorities weren’t sure if they had an actual, threatening aircraft bound for the Capitol on Tuesday, a gyrocopter (more on that in a minute) or someone’s hobby plane which strayed inadvertently into super-restrictive airspace after taking off from nearby Leesburg, Va. Congressional staffers trying to get to work didn’t know if they were facing another 9/11, a bomb, a chemical attack or a mass shooting.

The security posture at the Capitol went to “Air Con Orange,” the status designating Washington is under threat from an incoming aircraft.

“We were really scared,” said another Congressional source who asked not to be identified. “Even some information makes you feel better.”

Complaints from angry and rattled Congressional chiefs of staff and even lawmakers themselves flooded the inboxes of Congressional security authorities. A coalition of dozens of House chiefs of staff fired off an angry missive to USCP Chief Steven Sund.

“There were no corresponding alerts sent via email, text, PC pop-up window, audible alarm, siren, or verbal announcement to staff. This is highly problematic due to many of us and our staff already being in the building or in transit,” fumed the chiefs of staff to Sund. “Additionally, as of 1:00 pm, there was no corresponding ‘All Clear’ given.”

The chiefs of staff then asked to know the current protocol for alerting people of threatening incidents at the Capitol. The chiefs also inquired what goes into triggering an alert and questioned how USCP will alert people when there is an incident.

By midday, House Sergeant at Arms Paul Irving released a memo explaining what happened – and issuing a mea culpa.

Irving told the Congressional community “there was a report of a possible aircraft in restricted airspace. In an abundance of caution, USCP began monitoring the situation for any potential threats, and as a result, access to the Capitol Complex buildings was restricted for a short time.”

In his memorandum, Irving told the Congressional community they had to do better.

“We acknowledge that communication must be improved, and my office and the USCP are working to refine communication protocols and alert systems during significant events, wrote Irving.

Senate Sergeant at Arms Michael Stenger sent a similar missive to the Senate community.

“If the incident had escalated requiring staff to take action, USCP was prepared to send out the appropriate messages,” wrote Stenger.

That said, it’s still unclear whether an aircraft actually pierced restricted airspace encapsulating Washington. USCP scrambled a helicopter that circled the Capitol grounds. As is standard in the post-9/11 world, the Air Force dispatched jet fighters from nearby Joint Base Andrews.

“We don’t know what the hell it was,” said one knowledgeable source, noting it could have been a “weather anomaly.” Fox was also told it may have been “geese.”

This phenomenon is baffling because officials received information as to the location of the phantom craft, were told that it may have been “hovering” and were even given a readout on “knots,” measuring purported airspeed.

Fox specifically inquired whether Capitol security systems may have been hacked, or, if this may have been a “test” by terrorists to judge how people may have responded.

“That’s what they want us to do,” said one source familiar with Congressional security protocols. “Put our systems to the test, see how we respond and then plan around what we do.”

Fox is told neither scenario of a possible hack nor a “test” was plausible in connection with this incident.

This brings us back to the 2015 incident when disgruntled former letter carrier Douglas Hughes took off from Gettysburg, Pa. in a gyrocopter, little more than a flying lawnmower, and headed for Washington. Hughes managed to land the gyrocopter on the West Front of the U.S. Capitol to protest big money in politics.

There was almost no way to detect Hughes’s craft, let alone defend the Capitol against an incursion of this nature. It’s one thing to restrict massive aircraft to protect Washington against a 9/11 style attack with F-16s screaming through the air from Andrews. A smaller aircraft poses greater dangers. Put drones in that category. There’s a reason why “flying under the radar” is an idiomatic expression. It’s because, well, some things, like the gyrocopter, actually can “fly under the radar.”

After the gyrocopter incident, security officials tinkered with “dialing up” the sensitivity of systems that protect the Capitol. However, there’s a problem with detection. Buildings in downtown Washington emit radiation. Flocks of birds soar over the National Mall. The systems are bolstered too much, they pick up everything – and not just the real threat.

Over the years, USCP dramatically improved how they handle Capitol evacuations for possible air incursions. For a few years after 9/11, authorities used to simply dump all buildings on the Congressional campus, causing panicked people to sustain broken ankles and torn ligaments trying to flee.

Flushing the buildings also presented another set of problems. Perhaps potential terrorists wanted an evacuation so everyone would dash into the streets. Then, a would-be-terrorist would start plucking off people with a high-capacity rifle or launch a chemical attack.

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That’s why it’s sometimes better to shelter in place. Other times, it's better to run for your lives.

The biggest takeaway from Tuesday’s incident is that it may have been a “tweener.” Officials weren’t certain what was up. That made it a challenge to make a hard call on what to do.

The dearth of information looms large over this incident. And perhaps that’s because officials still don’t definitively know if they had a plane coming in or not.