Hi, after take off the plane just veers off to the left. Heading select will not work but LNAV will bring the plane back on course. I noticed a message on the screen which mentions the rudder. Could this be a clue to the problem.Thanks for any help.Rohen.http://forums.avsim.net/user_files/45298.jpg

"Could this be a clue to the problem."An interesting mental excercise, Rohen :-)The RUDDER RATIO System varies the authority of the rudder according to speed. At low speed, full rudder pedal deflection (initiated by the pilot) allows the rudder to move 26 degrees from neutral. At high speed, the rudder is only allowed to move 2 degrees from neutral.Rudder Ratio is controlled by one of two computers known as Rudder Ratio Changer Modules (RRCM's). The RRCM in control is chosen at random on power up. Airspeed data is supplied to the RRCM by its respective "SAM" (Stabilizer Trim and Aileron Lockout Module) ... more computers in the Equipment Center. The SAM's get their airspeed data from the Air Data Computers (ADC's)... yet more computers in the Equipment Center. The ADC's get their airspeed data from the pitot/static probes on the nose of the aircraft. These are heated to prevent blockage due to icing. This is done by the "PROBE HEAT" system. So, there is a (somewhat long) link between Probe Heat and the Rudder Ratio system. However, whether the RUDDER RATIO EICAS msg will appear as a result of probe heat problems is another matter (more manual reading required to determine this ;-)).Also, we are talking about the A/P here. The A/P has no direct effect on the rudder during takeoff, climb, cruise and descent. It is only during the final stages of autoland that the rudder is being controlled by the A/P. During the other stages of flight, the Yaw Damper system is automatically controlling the rudder to give proper turn co-ordination and, of course, "yaw damping". When the A/P uses the ailerons to turn the aircaft, a certain amount of rudder input may be needed. Any uncoordination would be sensed by the IRS's and they would tell the Yaw Damper system to provide the correct rudder adjustment. I suppose if you were making a sharp turn, you would probably need need a little more rudder movement than normal. If rudder movement is being limited in some way, it may make the turn more difficult to achieve. Since the Rudder Ratio system limits the rudder movement, a fault with this system could make turning more difficult. However, as previously mentioned, the movement-limiting is based on airspeed. The pitot/static system would have to be affected by icing in such a way as to produce a high airspeed indication. If the pitot tubes were blocked by ice, you would get a low airspeed reading (less ram air going in the tube). If the static ports were blocked by ice, I'm not sure how the airspeed would vary. Any pitot-static experts here? :-) If sea-level air pressure were trapped in the static system, during climb, would the indicated airspeed be higher than normal? Would the effect be as dramatic as having your pitot tubes blocked?Having gone down these lines of logic, you would then have to ask why the aircraft is turning with LNAV, but not HDG SEL. HDG SEL is affected by the bank limiter setting on your MCP. LNAV isn't. Is your bank limiter set at anything other than AUTO?Anyway, I could ramble on about this stuff all day, but I have the feeling that I have "lost" a lot of folks already ;-) In day to day life, engineers usually don't have to go into such deep thought. We'd fix the broken bits and carry out ground tests on the affected systems ... and let the pilots take care of the rest ;-) Cheers.Ian.

I think you just scared him away.

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But good post as always ;)

Hi again, thanks Ian for responding to my problem. Of course your mental exercise approach wasn