Could anyone come up with good explanations for this question...During rotation there was a master warning sound but no message displayed.Takeoff was done with flap 20. TO and CLB selected in the THRUST PAGE. In the TAKEOFF PAGE,I made the following entries FLAPS 20/1000 E/O ACCEL Ht 800 THR Reduction Ht 1000 for CLB RWY CONDITION...DRY V1 153 Vr 167 V2 175 I set the SPD Window on MCP to 185 and ALT window 3000All of a sudden after rotation and crossing over /around 1000 feet,there was a sudden loss of thrust ( not engine failure ) airspeed and altitude and the aircraft plunged headdown.At the same time the auto pilot was automatically disconnected but had to be connected again to continue climbingThanks for your tips and suggestionsKrisana

Control spikes from your joystick / yoke / throttle controller?Try disabling these and see if the problem re-occurs.If it is your controller at fault, FSUIPC has an option to smooth out these spikes.The Master Warning sound comes up when the AP disconnects, but that also annunciates on the EICAS screen.Andy Scholes.

There was no t " throttle disconnect " annunciated on the EICAS .What are the ' spikes " that you talking about.But why should the autopilot disconnected itself anyway ?Thanks Kris

Depending on the options set in the sim, your joystick throttle can override the A/T. MSFS and other sims seem to need a large and sudden movement to override the autothrottle. If you have an electronically "noisy" throttle, it can generate the type of signal which simulates this large/sudden movement.Overriding the thrust levers manually does not necessarily mean that your A/T will disconnect (with a Caution). If I remember correctly, the results also vary on the real aircraft. The autothrottle may go into a kind of dormant mode (like HOLD mode).Basically, if a throttle idle signal is being generated, the thrust is going to decay until you stall... and the Autopilot may not be able to control the aircraft. I'm guessing the A/P computers have disconnected because they can't control the aircraft.The solution is to put your joystick throttle to max for takeoff/climb, cruise and go-around... and idle during descent and landing.Cheers.Q>