Transponders have to be turned off while you're at the airport and while the plane's being serviced on ground. I think 777 has 2 transponders, so you also need the ability switch from one to the other. Lastly, I believe all electronics on the plane must be on a breaker circuit in case of electrical shorts so that pilots can isolate and turn off faulty circuits.
Although, I guess you could just check if the landing gear is up. I'm sure there are corner cases I can't think of, but it seems like that would pretty much cover it.
While this makes sense it may have to do what the poster above you said
Lastly, I believe all electronics on the plane must be on a breaker circuit in case of electrical shorts so that pilots :can isolate and turn off faulty circuits.
But you're right, ACARS (the system through which the engine information was routed - http://en.wikipedia.org/wiki/Aircraft_Communications_Address...) probably should be updated to add more information...