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Guest Krisana

Takeoff and descend in V NAV Mode

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Guest Krisana

Dear friends,I have 2 questions to put infront of you for help.1st questionAfter takeoff with the auto pilot engaged at 500 feet, I always experience a sudden loss in the thrust,air speed and altitude...WHY ?I remember having read this topic ( if I am not mistaken ) in the manual but since then could not find it again.2nd QuestionThis has to do with the descend in V NAV Mode.While flying from Bangok to Calcutta in India using PMDG route BKKCCU 001, The last way point (AVPOP ) before reaching CEA VOR ( Calcutta ) had the speed and altitude restrictions of 260/10590.One way point further up AVPOP name ESDOT was calculated by FMC at time of takeoff from Bangkok to have 320/FL350.When T/D appeared on the ND,I changed the altitude on the MCP to 10600 but when the T/D crossed and disappeared from the ND,the aircraft descended to FL 330 and refused to descend further.More than this the speed at time of " HOLD " in the PFD went right through the red tape and FMC message..".Drag required" popped up.I waited for the aircraft to descend on its own until reaching CEA VOR but that did not happen.I finally had to descend usuing the V/S mode.Could anyone throw some lights on both of my questions ?Thanks

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Guest Loiosh

#1: What is your CLB rate set to and what is your Cost Index? When you activate autopilot and have the Auto-Throttle enabled the airplane will adjust to fly at the proper power rating that you have set to make its climb-out. If you give it a high Cost Index (>40) she will fly slower and make more conservative turns.I suspect when you activate the autopilot the airplane is going from TO/GA ( at 100% throttle) to CLB mode (less throttle).#2: If you change the MCP's altitude after the T/D, make sure to press the altitude wheel (on the airplane you would actually depress the altitude wheel) to let your airplane know it is safe to begin descent.

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Guest Krisana

Thanks for your help.Please note that the takeoff was made in V NAV and L NAV modes.Wasn't the aircraft supposed to climb out usuing the information given by the FMC.The PFD did have " V NAV SPD " displayed in green .The thrust was selected at full TO and climb was armed at CLB.However I put the cost index at 100 %.If it is what you are suspecting that TO/GA changes to CLB mode during takeoff,how can I prevent this to happen again. 2) I changed the altitude window at about 10 miles from the T/D point and even after passing the point,the plane did not descend.I did press the altitude knob but nothing happened.She remained cruizing at 33000 feet.Kris

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