Does anyone know if there is some sort of system to the callsigns FedEX assign to their flights?

Uh, Not to be a smart aleck but, yes, I'm sure there is a system they use to assign flight numbers to their schedule but the callsigns would always be FEDEXxxxx as far as I'm aware. Those designations could very well be randomly generated. It's also possible that those flight numbers correspond to a destination and a schedule rotation or some other attribute but I would tend to doubt it. Just a guess.

From FlightAware i can see that the format of FedEx callsigns are:

 

FDXn

FDXnn

FDXnnn

FDXnnnn

 

I also guess there is some kind of randomization, but its very hard to see if it its also based on e.g. destination, time, weekday, aircraft-type and so on?

Well, from what I can gather, as I live under the Asia-MEM track and frequently see Fedex MD-11's and 77F's those flights all have FDXnn callsigns.

Interesting. I have checked some FedEx callsigns and I have FDX93 with the following routes on the same day:

 

KEWR - PANC (B77L)

PANC - RJBB (MD11)

 

So here we have the same callsign on the same day for to routes and two different aircraft types.

 

I also have callsign FDX28:

 

ZSPD - PANC (MD11)

PANC - KMEM (MD11)

 

So I guess it could be like this:

 

Flights to Asia: FDXnn and uneven numbers.

Flights from Asia: FDXnn and even numbers.

 

This theory is somewhat ruined though by FDX5060:

 

RJAA - PANC (B77L)

Interesting. I have checked some FedEx callsigns and I have FDX93 with the following routes on the same day:

 

KEWR - PANC (B77L)

PANC - RJBB (MD11)

 

So here we have the same callsign on the same day for to routes and two different aircraft types.

 

I also have callsign FDX28:

 

ZSPD - PANC (MD11)

PANC - KMEM (MD11)

 

So I guess it could be like this:

 

Flights to Asia: FDXnn and uneven numbers.

Flights from Asia: FDXnn and even numbers.

 

This theory is somewhat ruined though by FDX5060:

 

RJAA - PANC (B77L)

 

 

I think you are right. I know form Asia we have FDX 24, FDX 70, FDX 90, FDX98, and FDX 94 (might have been a one-off the other day.)

You should download EditVoicePackX.

Interesting. I have checked some FedEx callsigns and I have FDX93 with the following routes on the same day:

 

KEWR - PANC (B77L)

PANC - RJBB (MD11)

 

So here we have the same callsign on the same day for to routes and two different aircraft types.

 

That's a common practice on all airlines (at least in the US), for example I was on a USAIR A321 flight to KPHL from KBOS , it had continuing service to Europe (I forget what city) with the same flight number but on an A330. It could also happen due to a maintenance issue!