please help, speed controlling

[Guest proflight]

Hi all, I am now starting to pull my hair out (what is left of it) when i am in autopilot how do i control the aircrafts speed, i seem to set a speed using the speed knob but the aircraft seems to do as it pleases. This is the airbus pro panel. Would some kind soul please give me some tips on what to push and pull and to when to do it, thanks in advance.Terry

[Guest vrandar]

You need to get to grips with the concept of managed speed and selected speed.Managed Speed: this is where the speed is being controlled by the computers, specifically the MCDU (where your flight plan is etc). In the cruise for example managed speed will normally be mach 0.78. To go to managed speed you left click the speed knob which is the equivalent of pushing the knob. Think of pushing the knob( left clicking) as pushing control onto the computers. With managed speed what you will see in the window above the knob is ---.Selected Speed: this is where YOU select the speed. You left click to the left or right of the speed knob to select the speed you want: for increments of 10 you right click to the left or right, for increments of one you left click, then right click the knob itself which is the equivalent of pulling the knob. Think of selected speed as pulling control to you. With selected speed what you will see in the window above the knob is the speed you have selected.When to use them: Most of the time you will be in managed speed. For example in the F-PLN page of the MCDU if you entered a Standard Instrument Departure (SID) it will usually already have a constraint of 250/FL100 (250 knots below 10000 feet) entered. If not, you can do this yourself after takeoff by going to selected speed and dialling in 250. You would ten be on managed mode until well into the descent. I would normally reduce speed to 210 when I select flaps 1, then to 160 for flaps 2 and gear then go to managed speed at 4 miles flaps 3 or full.The concept of managed and selected is at the heart of Airbus operations and applies to heading, altitude and vertical speed (in feet per minute). In all cases, for managed mode you left click to push control onto the MCDU (managed mode) and right click to pull control to you (selected mode).I hope I have explained that clearly, but do come back to me if not or if you have any other questions.Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk

[steveark 0]

When under Auto Pilot, and at cruise, I find that the 'puter wants to run the craft at Mach 0.81 which is over speed. Seems every time I let the puter take over, this happens. I have never seen Managed speed of 0.78 automatically. I always have to over ride it by leaving the craft on Auto Throttle, but manually setting the speed to Mach 0.79. The plane will then maintain that speed without over speed warnings.Cheers!

[Guest vrandar]

In case anyone reading this is not sure what Cost Index is all about, a lower cost index results in a slower, steeper climb that gets you to cruise altitude sooner, increasing the time at optimum altitude. It provides a slower cruise mach and a shallower descent profile.A higher cost index results in a faster, more shallow climb, gets you to cruise altitude later, decreases your time at optimum cruise, provides a faster cruise mach (so you burn more fuel) and uses a steeper descent profile.So it could be your Cost Index which is causing this. In the cruise in the image below I have set the Cost Index to 20 (British Airways standard Airbus cruise CI at the moment, it's 0 for the climb) and you will see it has dropped the ECON cruise speed to about mach .67. If you have set your CI too high before the flight this might be causing your problem.http://forums.avsim.net/user_files/180567.jpgTo keep things in managed mode, before the flight you can set the speed through the PERF page of the MCDU (scroll through until you reach the CRZ page). Enter 0.78 into the scratchpad and press LSK4L. That will change the Active Mode at LSK1L to read "MACH .78" You can also have a similar effect through changing the Cost Index.During the flight you cannot use LSK4L on this page so, as you do, you set the speed through the speed knob on the glareshield, say to .78, and that updates the Active Mode in the PERF CRZ page to read "MACH .78" but you are of course in selected speed. To go back to managed just left click the speed knob.As to autothrottle, the Airbus is designed to be flown with it on throughout the flight. It goes on automatically on the take-off roll (check it is at 80 kts) and will disconnect on touch-down. In normal operations you shouldn't need to switch it off. Sorry, re-reading this I don't think I've described it very well.Rob Elliott, EGPE InvernessPSS Airbus Support andAirbus Fleet Training Captain, British Airways Virtual airbus@speedbirdonline.co.ukhttp://www.speedbirdonline.co.uk/airbus.htmlhttp://www.bavirtual.co.uk