This is just not the case. EO speeds are a compromise between acceptable single engine cruising levels and obtainable TAS's. The TAS thingy is of course a function of your single engine 60 minute range from which your ETOPS certification is derived. There are quite significant trade offs in each direction (altitude/fuel and range)
Just thought I might add a bit here, from the 737 point of view. While published speeds for single operation
are a trade off in altitude/TAS performance, the aircraft commander is not obliged to operate the aircraft at these speeds, and may select the speed shedule to achieve a particular goal. An example:
Flying along at F370 a 737 crew suffers a non-catasrophic engine failure. The following steps indicate one thought process:[list=1][*]The aircraft obviously cannot sustain its two engine cruise speed (or indeed any speed) at this altitude. As it begins to slow down you have time for a PAN call to indicate to ATC that you will begin descending.[*]You must decide whether or not you will turn off the airway for the descent - this depends on the traffic on the route and the distance between adjactent airways. Lets say in this instance you turn off the airway, in order to parallel it at, say, 10 miles separation.[*]ATC need to know your level off altitude. The ENG OUT page on the FMS gives the current maximum altitude for your weight and list the target speed for that altitude, which is the minimum drag speed indicated on the EFIS by a green dot. At our typical operating weights you have a 50% chance that this will be above F200, keeping you in controlled airspace, or above terrain in very high mountainous areas - in Australia staying within CTA is of interest so you look at this altitude, pick the next lowest hemispherical level in CTA and pass this to ATC as your level off altitude.[*]You now (still on descent) complete the ENGINE FAILURE AND SHUTDOWN CHECKLIST, turn to parallel the airway at 10 miles and level off at or just above green dot speed.[*]Decide where you are going to divert, accounting for weather, runway, services etc.[*]In our company you now have three easily available speed schedules to choose from. In the QRH are altiude capability tables for Green Dot (the same as accessed through the FMS, One eng. inop. long range cruise (LRC) and 280kt One eng. inop cruise.
280 kts is the speed selected for the 737 ETOPS operations for our operation.
LRC is close to green dot, and will keep you (hopefully) within CTA, whilst 280kt will get you home faster, but will require leaving CTA (the CTA base over most of Australia is F200). Both green dot and LRC are below the higher manoeuvering speeds introduced for the 737 rudder controller.[*]Make your speed schedule decision based on fuel, traffic, distance to divert and increased manoeuvering speed, select your new max altitude, advise ATC of any required descent, get traffic, change frequency and begin the diversion.[/list=a]
Simple really!
