A horrifying internal memo obtained by WTSP-TV reportedly details an incident which some pilots believe may have been a “dry-run” for terrorists plotting another 9/11-style attack.

Delta Airlines pilot Wolf Koch told the news station that it is “very foolish” to believe that an attack similar to the one that occurred on Sept. 11, 2001, could never happen again. In that attack, the deadliest on American soil, more than 3,000 people were killed.

In fact, Koch and other flight crews are worried that terrorists are already planning future attacks.

The memo obtained by WTSP-TV, which originated at the union that represents pilots for US Airways, reportedly states that “there have been several cases recently throughout the (airline) industry of what appear to be probes, or dry-runs, to test our procedures and reaction to an in flight threat.”

Terrifying Internal Memo Warns Terrorists May Be Doing Dry Runs for Next 9/11 Style Attack

WTSP-TV

“What most security experts will tell you that if a dry-run is occurring, the attack will shortly follow,” Koch said.

A Sept. 2 flight from Washington, D.C. to Orlando International is the most recent “dry-run” that the pilots are aware of. According to crew members, four “Middle Eastern” men caused a disturbance shortly after take off.

Witnesses say one of the men got up form his seat and ran toward the flight deck door. He then made an unexpected left turn and entered the bathroom for a “considerable length of time.”

Meanwhile, the other three men were reportedly seen roaming the cabin, changing seats and opening overhead bins to make a “scene” and possibly with the intention of distracting flight attendants.

Terrifying Internal Memo Warns Terrorists May Be Doing Dry Runs for Next 9/11 Style Attack

WTSP-TV

Terrifying Internal Memo Warns Terrorists May Be Doing Dry Runs for Next 9/11 Style Attack

WTSP-TV

The Transportation Security Administration (TSA) told WTSP-TV that the incident did indeed happen but that it doesn’t require any additional investigation.

“They’re flat-out liars,” a Federal Air Marshal said of the TSA’s stance.

The unidentified Air Marshal, who is prohibited from talking to the media, says the incident that occurred on Flight 1880 is serious, regardless of what the TSA claims.

“We’re waiting for the next 9/11 to happen, because it’s not a question of if. It’s a question of when,” he said.