From FAA JO 7210.3:1
21−4−1. DOMESTIC EVENTS NETWORK (DEN)
a. Domestic Event Network (DEN). A 24/7 FAA sponsored telephonic conference call network (recorded) that includes all of the air route traffic control centers (ARTCC) in the United States. It also includes various other Governmental agencies that monitor the DEN. The purpose of the DEN is to provide timely notification to the appropriate authority that there is an emerging air−related problem or incident.
b. Required ATC facility DEN participation.
- All ARTCCs.
- All facilities in the National Capital Region (NCR).
- Approach control facilities must participate on the DEN during President of the United States (POTUS) TFRs, National Special Security Events (NSSE) affecting their area, or when directed by System Operations Security or the DEN Air Traffic Security Coordinator (ATSC).
- ATCT must participate on the DEN during arrival and departure phase of POTUS, Vice President of the United States (VPOTUS), First Lady of the United States (FLOTUS) movements, or when directed by System Operations Security or the DEN ATSC.
- If the ATC facility is not actively monitoring the DEN or have a dedicated line to the DEN, they should call into the DEN directly via [redacted].
- All communication regarding real−time security concerns and operational impacts should be initiated and coordinated on the DEN. The premise of the DEN is a need to share versus a need to know.
- The DEN is an open mode of communication and is not intended for classified information.
The DEN was established in the aftermath of 9/11 to provide an "always-open" line of communication between FAA HQ, ARTCCs, and other relevant agencies. Various events trigger reporting to the DEN, including but not limited to aircraft accidents, suspicious aircraft activity, and ATC facilities going ATC-Limited or ATC-Zero (inability to provide services).
1I would link directly to the HTML version of the order but it seems to be unavailable at the moment.