This is addressed to anyone in the airline industry who might have some knowledge about airline cruising speeds and flight schedules. I read a recent earlier post on here in which a 757 pilot mentioned that his company's dispatch office will monitor his aircraft's position and ETE, then prompt the flightcrew via ACARS to adjust the FMC Cost Index if need be to allow the flight to maintain the correct time schedule.I've always wondered how this works, how a commercial flight can arrive on time despite changes in forecast winds and ATC deviations. I thought that flightplans had to be filed with a designated cruising speed and that such a speed would have to be maintained unless ATC approved a speedup or slowdown. How does all this come together? Thank you.

Voodoo......or PFM (Pure Freaking Magic)In flight, under radar coverage on the usual VHF communications it is quite normal. ATC modifiers a lot of things based on pilot request like speeds and direct routes etc, etc. ACARS is also VHF based now so the plane has to be within VHF range to get updates. (YES Sat-Comm is coming so you can put away your keyboards those of you getting ready to chime in).Long distance over water is a different ballgame. The OCEANIC clearances are over tracks with known Lat-Long waypoints. Based on performance a crew can run a "How Goze-it".Unless a clearance to change speed is obtained in normal operations we are stuck with what we have filed. Working HF is a pain at time (YES Sat-Comm is coming so you can put away your keyboards those of you getting ready to chime in) so we don't fiddle with CI till we are back in Radar coverage.The published schedules themselves are constaintly changing. If you look at the times for the same airplane, same airline, same city-pairs you may see a different enroute time based on time-of-day. Marketing knows if a flight goes into a Hub city at peak during a bank for another carrier, the load on atc is more and a delay is incurred.The suits also look at a lot of past history when making up schedules and the data is good starting point. This includes de-ice times etc in winter, frequent T-Storms in summer etc.When a flight is closed out a msg is sent to company dispatch. In that is incorporated a code for operational delays (late PAX, deice, ATC, bags, Wheels & deals, WX etc). If a trend is noticed then the cause for the delays are addresed-floggings of the ground staff, clocks adjusted.......Ever wonder why the plane is pushed back from the gate about 6 ft and sits for 20 minutes?. Timothy

Thanks, very insightful :) Don't take life too seriously- you'll never get out alive anyway

Question on the Cost Index. Supposedly we are to put in a value of .80 in this FMC block. Does this mean if we use a smaller number, then we go slower and save more money/fuel? Terry

Why don't you try it and see what happens to the speeds on the vnav pages?Regards,Wade

On time is all relative, really. =) But just as an aside with measuring on-time performance and the accuracy of PIC and FS2002, yesterday I simulated UAL 906 (Newark to London Heathrow, UAL flies a 777 on the route, I used PIC).Departs 1930, Arrives 0730 (next day). Due to favorable winds over the Atlantic, I arrived at just about 0705. Looking at United's website today, flight 906 arrived 24 minutes early, at 0706. Scary...Jon (KSEA)

I had the same deal on a EGLL-KLAX route - arrived within 3 minutes of the real thing that day...scary indeed.Rob.