B777 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 233; Flight Crew Total 15462; Flight Crew Type 1594.3
Communication Breakdown; Troubleshooting; Situational Awareness
Aircraft Equipment Problem Critical
Flight Crew Returned To Departure Airport; Flight Crew Landed As Precaution
Aircraft; Human Factors
We had a mechanical (No Airspeed or ALT on our ISFD) that we as a crew decided it was not a safe action to continue to fly across the Atlantic at night IMC.  We had great communication with dispatch; [maintenance] and the Fleet manager. The [decision] of the fleet manager/[operations] was to continue. We as a crew felt that it was not safe so we did and air return back to ZZZ. I am still wondering why they think it was OK to continue as if we were left with only the ISFD we would only have attitude but no Airspeed or Altitude. We ran all the checklists; took things slow; properly handled the situation in a calm professional manor. The one thing we did do was dump an extra 15K (estimate) of fuel. We did not land over weight but we landed probably 10-20 K lbs under Max Landing weight.
[Report narrative contained no additional information.]
B777 flight crew reported after takeoff the standby artificial horizon was not giving any altitude or airspeed information.