Entering VNAV speeds in the CDU

[Guest tyrant]

Hi there,When i try to enter my own vnav clb speeds, it wont allow me, saying my inputs are invalid, this is when i try to enter a ias and a mach together using the format xxx/.xx however it will allow either an ias entry or a mach entry. is this an issue or was it designed this way?? If the latter why?? is it like that in the RW, and why can it be done in other payware addons??Another thing is when i was on short final i disconnected the AP, thus showing a red EICAS msg saying autopilot disc (i think) anyway, once on the ground, i could not cancel that red msg no matter what i tried.ThanksJason

[Guest NormanB]

Jason,The reason you can't enter both numbers is that during a climb the mach number changes constantly based on the altitude density i.e. at FL200 an airspeed giving Mach .56 is going to increase to give around Mach .75 at FL300.You do know that you are supposed to cancel ALL warning messages when they occur if they are MANUAL EVENTS i.e. you did them?

[Guest tyrant]

Ok, i understand, but the purpose of the two numbers is as is with the default cost index figures, so you will fly ias to until the mach number desired is reached and from then it is flown on the mach number. ie. i want to do a 320/.840 climb not a 310/.82 climb. It seems a little silly to muck about with the cost index until you get it right.With ref to the AP, i disconnected at about a mile final, once landing roll complete, i re-engaged the AP bar and tried to cancel the alert, was the time difference too long??Jason

[Guest NormanB]

You dial in a CLIMB NUMBER in IAS you dont try to climb at mach.......... the computer just tells you what the number is based on current density altitude. As far as the AP yes in a normal cockpit when a manual event takes place the PNF ( Pilot Not Flying ) would cancel all alarms after they are noted.

[Guest tyrant]

Ok, but in the RW all aircraft climb and crz at a mach number above a certain level.Jason

[Guest NormanB]

Above FL230 generally.

[Guest tyrant]

Ok, now, how does the FMC work out an accurate TOD point if you cant put the 2 speeds into the CDU. On the VNAV des page when approacing Dubai it was giving a default of .73/273, so thats what TOD point is caculated with is it not. I want to descend at .84/320, now if you cant put those two speeds in, how is the TOD point caculated, if you just put in .84 it should calc .84 all the way down to 10000 feet which would have you doing about 400kts ias at some stage. If you enter just 320, then its going to accellerate to close to mach 1 in the initial part of the descent.Am i being dumb?????????Jason

[Guest NormanB]

Jason,You can climb or descend on one figure or the other. Both figures are not the same at different levels.Ie you can decend on a mach number or a speed.

[Guest Sjaako]

Hi,In the real world you can put ias/mach in the VNAV page. works on CLB and DES page. VNAV will fly the IAS till it gets to the MACH nr and vice versa in the descent.Autopilot Master Warning:The first press of the Autopilot disconnect switch on the control column disconnects the AP. the second press:-Resets the master warning lts-Resets EICAS warning msg-Resets the aural warning.Cheers Sjaako

[Guest tyrant]

Thanks Sjaako,What would happen if just entered one speed in the RW, if you just put in an IAS in the CLB then you would have to manually change it to mach when you reached your desired mach speed. I thought one of the benefiting factors of an FMC was to automate things a lot more so when you're are on the GND you can select your climb profile and not have to interfere all the way to the CRZ.Jason

[Guest NormanB]

> I thought one of the benefiting factors of an FMC was to>automate things a lot more This was my basic understanding too. Im as interested as you now Jason.

[Guest Sjaako]

Hi Guys,If you enter just an IAS it will accept it but fly the IAS all the way to TOC (CLB example). Which means it would start to overspeed when the Mach nrs become more limiting. For instance at FL370 the Mach nr is .84 the IAS is somewhere round 270kts. so if you would climb with constant IAS in the VNAV clb page i.e. 300kts it would overspeed at some point before FL370.You have the option to alter the speeds but don't have to. Econ speeds also work but when flying cost index 0 it gives around 250kts descent speed. This is when most people put in .84/300kts or anything along those lines.If you change a CLB page speed/mach nr. it only changes the CLB speed CRZ and DES remain unaltered.Cheers Sjaako

[Guest tyrant]

Thanks SjaakoSo what you are saying, which is what i believe to be correct, is the real world procedure if you were overiding your cost index econ speed is to enter two values, an IAS and a Mach. Likewise with the DES.Normanany comments on the findings of my flight with ref to some of those issues?Jason

[Guest Sjaako]

Normally speaking YES.Unless you fly a very short sector i.e. FL100 then you would not use mach nr's.So 99% of the time I enter IAS/Mach nr. in CLB and DESand Mach nr in the CRZ page. (In the CRZ page you can enter IAS OR Mach nr.) not both.Cheers guysSjaako

[Guest tyrant]

Thanks SjaakoThat is exectly what i understood to be real, thats why i was so confused when i was faced with this limitation.PSS, something to look at!!!!Jason