So we have somebody that contacted ATC via a Facebook post. Suppose I saw that Facebook post and believed it to be a genuine emergency. How can I contact ATC?
Call the police if in doubt who to call they have contact with Air Traffic Control.
Also calling the wrong facility can mean that it can take quite a while for the information to make it to correct facility.
Finding direct line phone numbers to ATC facilities can be intentionally hard. Prank call anyone! They are usually somewhere in the local Aeronautical Publication Books but where you can get a copy of them and then finding the number inside the book is difficult. Just call the police!
In a recent conversation with an FAA DPE, he was telling a bunch of us about a plane crash he witnessed as it happened (he was at the field where the airplane was attempting to make an approach in dense fog, which eventually resulted in a crash).
The DPE's first instinct was not to call 911, as he saw others in the vicinity doing that. He instead called the tower of the nearest CLASS C Airport (KDAB) with whom the aircraft would be in control of under an IFR Flight Plan.
He had KDAB tower's number on his cell (DPEs usually carry numbers of all nearby towers and important Aviation Authority Offices such as FSDO, NTSB etc.). If he didn't, it's not hard to get the number these days. Internet, ForeFlight, AFD - many resources.
Why did he call the tower? Several reasons:
- He reported the crash to them (the pilots, according to him, didn't look like they would have survived the spin that resulted in a crash)
- He told the tower not to expect a phone call to close the IFR Flight Plan (regulations would require a Search and Rescue operation within an hour after the ETA on the flight plan unless closed)
- The tower would have more information about the Pilot and any contact number at the destination (from the Flight Plan). This would help the authorities on the ground.
Point is: who to call, when to call, how to call and what to report would depend on the nature of the emergency.
E.g.: If you're in a remote place with no one else around and you witness an emergency, your first call should be to get help.
Hope that answers the question.