There are two conditions:
1) ETOPS Route validation. It means the route must be within the circles with centers on adequate airports and calculated according to the single engine approved speed per time (still air).
2) Fuel critical scenario. It must include the engine out fuel calculation plus decompression, emergency descent fl100 etc... and consider the higher fuel.
Normally the planning system would use a IAS (costant value), to be then converted in TAS at 10.000ft (then you would see a critical fuel scenario showing different TAS).