Long Range Cruise

[Guest john_omaha]

Recently I had a chance to look at a real world arline flight planning program. They demonstrated a LRC flight from LAX to SYD on a 747-400. Why does PMDG 747 LRC mode start at a low speed, ie M83, and end in a higher speed, ie M86. The demonstrated flight plan was for a fully loaded aircraft for that distance and the LRC mode started at M855 (FL300) and ended at LAX at M835. I don't know if anyone can answer this, maybe a real world 747 pilot?ThanksJohn McGinnis

[martinboehme 492]

Maybe it was due to the forecast winds?Martin

[rsrandazzo 6,353]

John-The data used for the PMDG 747-400 was provided by the manufacturer- so we are certain of it's accuracy.In real world conditions the speed may be adjusted to account for winds. Rule of thumb is that the lower the imapct of the winds on your nose the slower you go... the higher the impact on your nose the faster you go....In your flight plan (barring other things like company ops procedures that dictate this speed change) i'd expect to see higher winds on the initial portion of the flight and lower toward the arrival side.

[michal 44]

With no winds it should start with higher speed and end with lower.Michael J.

[Guest Cindy_Zoonan]

Turbulence penetration speeds decrease with a decrease in weight to limit the force experienced by the structure during a sudden, abrupt acceleration so it makes sense that aircraft cruise speed, if flying at very high airspeeds, would decrease as fuel is burned off and weight is reduced.