On most supported planes the Air plugin reads the MCDU screen lines content on X-Plane through specific datarefs specified in their config files and sends them to the app using the air UDP protocol which runs between ports 59900 (computer) and 2425 (AirFMC).

The Boeing 757, 767 and 777 from Flight Factor and with the CRJ-200 from Javier Rollon are an exception to this however. This is because this set of planes share common developers and a different way to make their MCDU screen lines available; instead of using datarefs they are accessed by an IPv4 TCP connection to port 18387 of the computer running X-Plane.

On these planes sometimes AirFMC will display a blank screen while the key presses will work. If this happens it is most likely a firewall or anti-virus issue. When detected, AirFMC (the app on the iPad or iDevice) will attempt to connect to the computer running X-Plane on this port periodically (a few times per second) to retrieve the screen. If the firewall blocks incoming TCP connections by default (which most do) it won't allow this to happen and the screen will appear blank.

The solution is to allow this type of connections using a specific rule; the HOWTO depends on the firewall or anti-virus in use.

1) Start by disabling any firewall and anti-virus to check which is causing the problem.

2) Configure a firewall rule which reads more of less like:

PERMIT TCP IN ON PORT 18387 KEEP STATE FROM ANY TO ANY

If you know the IP address of the iPad and computer and these are fixed you can specify these on the FROM and TO instead of ANY. Alternatively you can also just enter the local subnet (such as 192.168.1.0/24 or whichever is yours) in FROM and TO.

Alternatively, we've also heard reports of VPN adapters and configurations creating problems. Try disabling these if you have one too.

In summary if the screen appears blank:

Something is blocking incoming TCP connections on port 18387 on your computer. You'll need to configure appropriately to allow these connections. Also check VPN interfaces and that these are disabled as they may interfere.

If you have examples of firewall configurations that made this work, we'd love to hear and share them with other users.

Fun flights,
The Haversine Team