FMC Cruise speeds.

[Guest venquessa]

I know that by default the FMC tries to pick the best possible economy climb/cruise and so on...I did a flight last night from EGAA to EGFF (Belfast to Cardiff) as I am going on this very flight at the end of the month. From the flight booking departure is at 11:40 and arrival is at 12:40.I left the gate for push back at 11:38. The standard preferred route is along an airway with a FL245 limit. So I cruised at Fl240 (even though it's an easterly route, but 230 seemed a bit low to me).The FMC choose to fly at (I believe) 280 knots. It might have been 290. Setting it to LRC gave me a lower speed. I found this odd, because usually the LRC at higher alts gives a faster speed.Anyway, I thought that 280/290 was too slow, so I enter 320 as the speed.When I arrived at EGFF without any delays, straight descent to FAP and ILS landing, taxied to the gate etc. It was 12:36. 4 minutes early. 2 minutes shorter travel time.En route I had a pretty cracker tail wind too, about 58knots of it.I susspect if I had of stayed in ECON mode I would have been 10 minutes late.Is it normal SOPs to run faster then econ on short routes? This one was only 285 miles IIRC.

[crvm]

As per Bulfer's 737 NG GUIDE - "..."For cruise within 2000 ft of otimum altitude:700 LRC approximated by .78M800 LRC approximated by .79M""...Flying LRC reduces the number of power adjustments necessary to maintain proper speed, but results in 1% fuel milage penalty."" Now talking about FMC generated speeds in general terms like what we think should happen is not quite correct. ECON is based upon primarily on CI entry. "Too slow" is meaningless in terms of onvenience over cost factors. It's either time is more important or fuel is more important. That's the company's choice in a given CI on the flight dispatch. As a simmer you already know that 280 knots at higher altitudes does not mean 280 knots at ground speed. I susspect if I had of stayed in ECON mode I would have been 10 minutes late. If you input the FMC with the correct or close forcast winds this of course would not be true. Plus in such a short flight I seriouly doubt you would have varied by such a extreme time factor as that. Best Wishes,[h4]Randy J. Smith[/h4]http://www.rawbw.com/~bdoolin/shinault/Animation1.gifCaution! Not a real pilot, but do play one on TV ;-)AMD 64 3200+ | ASUS KV8 DELUXE | GFORCE 5700 ULTRA @535/1000 | Maxtor 6Y080M0 SATA 80 GIG | 512 DDR 400 | Windows Xp Pro | Windows Xp Pro 64 |