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747 FD commanded speed

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Hi,I'm trying to fly a departure manually EGLL, DOVER SID, but for some reason the FD commands 170 knots even after acceleration height. It does not command lowering the nose in order to accelerate.LNAV and VNAV are armed on the ground and engage propery after takeoff.As far as I know above acceleration height (1000ft) it should command lowering the nose in order to start accelerating for flaps retraction, however this doesn't happen, it tries to keep it at 170 knots.Only thing that helps is deleting the 6000ft crossing restrition found on the LEGS page. There are no speed restrictions on the LEGS page, and only the usual 250/10000 at VNAV CLB page.Am I missing something?Cristi

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Hi guys,if any of you could help me on the problem above, that would be great :)Cristi

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Any chance you could post some screenshots of your panel when this is happening?


Mike Roth

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Salutari Cristi,The the speed should jump from the set V2 in the MCP to 250 knots (or greater depending on your weight - minimum clean speed). Confirm that 170 IAS is your calculated V2 (or V2 +10) and that the TAKEOFF, THR LIMIT and VNAV pages in the FMC are set corectly. If this happens on every flight please try to follow TRC lesson 1 and 2 to the letter and if it works see what's diferent in your preflight and change accordingly. Have fun,Eric Bocaneanu---RO-vACC 1www.rovacc.org


Eric Bocaneanu

ROvACC Director

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Notice that the SPD restriction is in small font and the altitude restrictions AT OR ABOVE. It is an estimation (170) but with a V2 SPD of 164 your target SPD will become 264 - not 170 (V2 +100). I thought that SIDS should have a BLANK spd line with the altitude restrictions (someone correct me if I am wrong but speeds are relitive for the aircraft in question). Anyway, modify this since the only true resrictions on SPD should be the aircraft's and or ATCs' which will be the aircraft's requirementif the spd in question is impossible for an aircraft of this type (i.e. 170). You could modify EPM by inputting 264/4000A or higher spd, depending upon flaps up SPD or clearance SPD etc. Simply enter 264/4000A at LSK 3R and press EXCUTE. Retract flaps on schedule. For DET it looks like a level off altitude until (XX?) but cannot see page two. You of course can input 264/DET29 or higher depending for DET wpt, and continue with the VNAV profile climb to cruise altitude or another level off ATC request. Best,Randy J. Smith


Randy J Smith

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V2 is 154 set V2+10=164 in the MCP as initial climb speed.Ok, but this 170 estimation seems wrong, because after the initial climb, acceleration occurs only until 170knots, and it keeps that until DET.I don't see any reason why I should enter that restriction, FMC should caclulate correct speeds for acceleration in the climb.Cristi

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V2 is 154 set V2+10=164 in the MCP as initial climb speed. Why would you place +10? It is V2, it is always V2 and although one airline does do what you say (United I believe),yet, Boeing and all others that I know use only V2. The F/D commands already place it higher automatically. Ok, but this 170 estimation seems wrong, because after theinitial climb, acceleration occurs only until 170knots, and itkeeps that until DET.I don't see any reason why I should enter that restriction, FMC should caclulate correct speeds for acceleration in theclimb. Sure IF you were not entering a SID that contains the relevant data for the departure. If you enter or have a restrictive ALTITUDE you also need to enter a SPD for it to work with VNAV engaged. That is why you MODify this departure to make it work correctly. Also, the FMC will calculate ECON-MAX/RATE-ANGLE SPDS not based upon waypoints but on performance. Your performance/SPD is based first upon flap retraction/min maneuver speed which well exceeds 170 knots. So, 254 knots if the min SPD I would place on EPM @ 4000. By the time you go flaps up you will be very close to this SPD and VNAV can be engaged and will command correctly. Best,Randy J. Smith


Randy J Smith

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