"My question was about a flight-idle, fixed IAS descent from altitude, (not maintaining a 3 degree glideslope or true/indicated altitudes etc.)". .. .Doesn't colder, denser air create more drag....and the more drag you have (with engine thrust being equal), the faster you descend?. .. ."Flight idle will give more thrust in lower ambient temps,....". .. .Not sure what you mean by "Flight Idle" thrust. Is this what your particular airplane produces when your Anti-Ice is switched on, or your flaps are in landing range? (i.e. high idle). Or do you mean normal idle in the first part of your descent from high altitude cruise? Or does your aircraft have different logic for idle?. .. .I've seen pics of cockpit engine displays during descent where the EPR guages are showing less than 1.0 during descent (i.e. aircraft engines with large intakes/fans at the front). I'm not an engine expert/aerodynamicist, so I'm guessing that a less than 1.0 value equals "drag" rather than "thrust"? Perhaps the colder, denser air equals more drag theory comes in to play here, as well?. .. .Rgds.. .Q.