Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Became Reoriented; Flight Crew Overcame Equipment Problem
Incorrect / Not Installed / Unavailable Part
During preflight loading of the takeoff data; FMS would not calculate V speeds or EPR.  RFO noticed that the TAT indication was well above normal.  Eventually the TAT started coming back down and soon the FMS calculated V speeds and EPR.  While the Captain student and myself were continuing with our preflight duties; the RFO deduced that the aircraft had sensed that it was airborne due to nose strut extension.  I do recall during preflight feeling the nose rise up; but it was not dramatic.The aircraft had been tethered with a [larger aircraft] tether as opposed to an MD-11 tether.  The additional length allowed the nose wheel to lift off of the ground sufficiently for the ground shift to sense airborne.All 3 crew members checked that the aircraft was securely tethered prior to entering the aircraft. However we were not aware that there are different length tethers and that interchanging them could cause a problem.
MD-11 Captain reported that during cockpit setup crew noticed the TAT indication was well above normal and the FMS would not calculate V speeds or EPR. Crew then realized ground personnel were using a tether from a larger aircraft that allowed the nose to rise enough that the flight/ground switch was activated.