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Pilot Joud

DES PATH UNACHIEVABLE: FMC Message when descending

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So i have been flying the pmdg 737-800 and every time i reach top of descent the plane does not descent and i get 2 messages saying 

DES PATH UNACHIEVABLE and set MCP altitude. Can someone please tell me how do i prevent this problem.

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Okay, first off I am willing to bet the FMC is saying "RESET MCP ALTITUDE." The reason the aircraft is not Descending at your TD is because your cruise or highest altitude is still set in the MCP itself.

 

Prior to reaching your TD say 10nm or so, no closer than 2nm set your cleared lower altitude or set the lowest altitude of your approach. Key thing is to set this BEFORE you reach your TD. If you do this, I guarentee the aircraft will descend. 

 

The reason you were getting DES PATH UNACHIEVABLE is because you (The Pilot) never authorized the aircraft to comply with VNAV since the MCP altitude was never reduced.

 

2nd method:

 

If you do happen to forget to set your lower MCP Altitude prior to TD, or ATC gives you your descent clearance later than the aircrafts calculated TD point. Then you need to set the lower altitude and then PRESS ALT INTV. This stands for altitude intervention and allows the aircraft to resume its descent profile. 

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Can someone please tell me how do i prevent this problem.

 

Neither are a problem. The one message is telling you to reset your MCP altitude to a lower altitude to allow the aircraft to descend. The DES PATH UNACHIEVABLE message means that the constraints will not allow you to descend to the proper altitudes on the STAR. This may mean that your planned descent speed is too low, or there's something that doesn't make sense to the FMC on the STAR. On STARs like the LENDY into JFK, this is normal and expected.

 

Also: full names - first and last - in the forum, please.

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So i have been flying the pmdg 737-800 and every time i reach top of descent the plane does not descent and i get 2 messages saying 

DES PATH UNACHIEVABLE and set MCP altitude. Can someone please tell me how do i prevent this problem.

You can prevent the problem by becoming familiar with the airplane by flying Tutorial 1 and reading the NGX Introduction Manual.

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Ok thank you for the replies everything is working fine and for my next post i will write my first and last name.Sorry i am new to avsim. :smile:

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for my next post i will write my first and last name.

Set it up so that is done automatically. Click on your user name in upper right corner, click on My Profile, click on Edit My Profile, click on Signature, in Edit Signature enter your first and last name, click save and your name will be on all of your posts.

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