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Guest A32X

Autoflight "Bug"?

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Guest A32X

Hi,My FMA isTHR HDG HOLD FLCH SPDClimbing at around ~240 knots I commanded an extra 10knots of speed. The aircraft pitched nose down very rapidly (full forward stick.) Can anyone reproduce this?-Paul

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Guest s_L_Y_F_a

since u got THR as the AT mode and u added 10 knots to the MCP speed the AP reduced VS so the plane can accelerate to the commanded speed( thrust cannot be added because THR is already the maximum allowable trust setting). This is quite normal but it should not happen rapidly. Maybe u got into a downwind stream and as a result your air speed dropped and the AP tried to compensate this by reducing VS faster than usual

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"since u got THR as the AT mode and u added 10 knots to the MCP speed the AP reduced VS so the plane can accelerate to the commanded speed( thrust cannot be added because THR is already the maximum allowable trust setting)."On the 744, FLCH does not always produce maximum allowable thrust. FLCH provides sufficient thrust to make the altitude change in a given time frame. However, large altitude changes invariably produce full thrust. Perhaps you are confusing it with THR REF?Cheers.Q

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Guest D17S

Hey Q, et al FLCH is a very interesting pitch mode. Consider this for a moment: It looks like FLCH is targeting a rate of climb based on the amount of climb selected. I'm seeing a ~1200 ROC for any selection that requires an altitude change of up to ~2000 ft. Then I see a (more or less) linier ROC increase up to about an ~8000 foot altitude change selection. I can watch thrust increase as I select an altitude further and further away from my current altitude. I can run thrust up and down (at will) by selecting altitude changes of between 2000 and 8000 feet. I can directly control thrust with the MCP's altitude select knob.Is this what is playing out? In FLCH, it looks like the Autothrottle's "THR" mode is increasing thrust bit by bit based on the amount of climb I have selected. The 'method to AT's madness' is to attempt to 'provoke' FLCH to increase its pitch to control an impending overspeed (remembering FLCH's 'prime directive' is to maintain speed by using pitch - Speed on Pitch). FLCH's resulting pitch up maneuver causes the increased Rate of climb "THR" wanted all along. With each increased altitude selection, "THR" just keeps bumping up it's thrust level until it gets to the current EICAS limit. A greater ROC simply and naturally occurs. "THR" is kinda goosin' "FLCH" to get what it wants. (Dang, sounds a bit too familiar!)The same happens in descent. Except the max ROD is determined by

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