>Tim Zukas: What single-engine cruise speeds are assumed for 757/767/777? The same for all operators of a given model?
For ETOPS planning, each operator chooses their own speed. The actual speed flown depends on the situation. A primary concern during a single engine divert in a 767 is to stay out of icing conditions because there is no way to de/anti-ice the inop engine. Flying at a lower speed may allow a cruise altitude above the icing. There may also be a benefit from nice tailwinds at higher altitudes.
The determination of an ETOPS area of operation is a relatively simple matter of referring to a table which Boeing has produced for its customers as part of the aircraft's ETOPS certification. The table is based on a theoretical straight line, no wind, standard day driftdown. The table is entered with an engine type, an assumed initial altitude and gross weight, and a driftdown speed chosen by the airline. This is all for flight planning, and the numbers generated are pesimistic; based on an instantaneous descent, anti-ice on, etc.