Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 60; Flight Crew Total 9500; Flight Crew Type 2000
Confusion; Distraction; Human-Machine Interface; Troubleshooting
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; Flight Crew Requested ATC Assistance / Clarification; Flight Crew FLC Overrode Automation; Flight Crew Took Evasive Action
Aircraft
Following the Loupe 2 SID; we were required to turn to a heading at 1.8 DME from the SJC VOR.  As we climbed out of 3;600 feet; I lost the DME signal on my side; I then asked the pilot not flying to call my turn; but he lost his DME signal about the same time.  As we checked on with NORCAL on 121.3; I stated; 'Please call my turn; we lost the DME signal.'  He asked us to IDENT; and gave us the required turn.  He then asked what happened; and the pilot not flying replied; 'Our FMS autotuned and we lost the DME signal momentarily.'On the taxi out for takeoff; we both displayed the SJC VOR along with the DME; and we had this during the takeoff and initial climb.  What we hadn't noticed was that the VOR on power up went to autotune; apparently a new feature with the new software revision loaded in the FMS.  As we climbed out; the autotune feature went to the LIN VOR as it got the signal; and dropped the SJC VOR.  As we followed the ATC given turn; the not flying pilot manually tuned in the SJC VOR and we got our DME back. This can be prevented by the following actions: More information on the subtle changes in the FMS when new software is loaded. Always manually tune the VOR for a vector departure. On subsequent trips that week on the same aircraft we noticed that on every power up; the VOR went to autotune. There was no deviations of altitude and airspeed; or TCAS event during the departure.
A fractional flight crew reported that a recent FMS software revision allowed VOR autotuning after takeoff which caused this flight to lose the departure airport DME for a required turn. The solution is to manually tune the VOR.