i think the only way to handle this in the MD-11 is to have one constraint and use the mcp altitude for the other limit. so for RIIVR you could have at or below 14000 as a crossing restriction and set 12000 in your mcp. then, after passing the fix, dial in whatever altitude is required for the descent then.

Denis

After I made the above posts, I flew the 747-400 into KLAX using the RIIVR STAR. It shows up in the flight plan in the CDU with the -14000 +12000 allready in it. Same database different results. Interesting.

Michael Cubine

i noticed the same thing flying the Boeing, Michael. the database is good i guess it's just that the Boeing FMC/MCDU is more... practical?

Hi,

 

i noticed the same thing flying the Boeing, Michael. the database is good i guess it's just that the Boeing FMC/MCDU is more... practical?

 

Compared to the NGX FMC I prefere the MD-11/Airbus FMC. It doesn't have the in between altitudes, however for me personally it's more comfortable to use.

Sometimes a STAR will indicate a between altitude. In the boeing FMC it would be entered: "RAINN 240/14000B12000A. Is this possible in the MD-11? Ruben

Since nobody seems to answer your question. No you can not. If you see that you are too high you set the 14000B and if you come too low you add 12000+. No need to have above and below on one waypoint since you most likely know where you will end up anyway...

HTH,

Manfred

Manfred you should have read all the replies. the question was answered.

Manfred you should have read all the replies. the question was answered.

 

Where is it answered?

The only answer that I found close enough was yours but it isn't perfect for all situations, let us say that the aircraft is a bit low (the restriction a bit high). Instead of trying to fly at an high altitude as possible before descending (and save fuel) the aircraft is going to descend to the MCP altitude and keep the lower altitude and burn more fuel. I know it is nitpicking as f*** but during todays high fuel prices :rolleyes:

 

The main reason I wrote the "nobody has answered" is because everyone wrote, i think..., and I do it this way... Nobody clearly answered: No, you can not enter both restrictions at the same time.

 

I hope you understand my side as well but you are right. I might have exaggerated a bit... :blush:

 

Regards,

Manfred

post #13

 

no, unfortunately you can not enter both.

 

besides, if you enter an altitude on the FCP that means the aircraft will not descent below that altitude. it will not make the aircraft descend to that altitude by the time you reach the fix involved.

 

so if you enter an at or below this would be the only restriction. entering a lower altitude on the FCP will ensure that you will not be lower than the altitude dialed in. in the above example (RIIVR) the aircraft will be at/below 14000 ft. putting 12000 on the FCP the airplane might still cross the fix at 14000 if that matches the descend profile. even if you put in 3000 the aircraft will still be on the descent profile unless the altitude restriction is above/below that profile.

 

correct me if i am wrong.

Gentlemen

 

You cannot program an In Between Comstraint in the FMS, additionally, if you program an "At or Below" descent constraint, the FMS will consider it as an "At" constraint".

 

Apart from that, I think this airplane is one of the best for FSX.

 

Best regards

Palle

post #13

 

Ahh ######. 13 is usually a lucky number for me :blink:

 

Denis, you are perfectly right, that way works good as well. I usually use the way described in my previous post. I have tried to illustrate them in a altitude/distance graph.

 

Your way

 

My way

 

In this very rare situation where the restriction are outside the perfect GS the aircraft will descend earlier than mine. That will cause it to fly at a lower altitude for a longer time and thus increase the fuel consumption. You will also get "increase air drag" messages (I think). In my way the plane knows in the planning phase that it can not go below so it will account for it and automatically adjust the flight for a more fuel economical way.

 

There is one large drawback though and that is that there won't be any upper protection. That means that if something changes unplanned (crazy wind ,cra**y planning or bad situational awareness) then there is the risk of missing it and come to high.

 

There are both advantages and disadvantages in both ways. I am going to use your way the next time I encounter such restriction to try it out.

 

I am sorry for missing your post but my way wasn't mentioned earlier so it wasn't totally useless B)

 

Regards,

Manfred

 

P.S. I am really tired so I hope that what I wrote makes sense.

...if you program an "At or Below" descent constraint, the FMS will consider it as an "At" constraint".

Sorry, but you are mistaken. The FMS treats the altitude constraints of "at", "at or below", and "at or above" seperatly and correctly. It's only restriction is that it does not deal with "between".

Hi Paul

 

Thanks for the feedback, by the way, I did a quick test using "Profile" during descent with an "At or Below" Constraint above the ideal FMC calculated descent profile and the FCP Altitude window set at a lower altitude, guess what, the autopilot leveled off at the exact "At" altitude until passing the waypoint, then continued the descent to the FCP set altitude.

 

The interesting thing though was that the FMC vertical deviation indication from the ideal descent profile was correctly displayed!!!!!!

 

Best regards

Palle

Showing at_or_below and at_or_above:

 

Wow guys! I left this thread for two years and decided to revisit it. To my surprise, there has been great developments (recent too!). I think the general consensus solution is the best option. It's possible this feature wasn't needed in the MD-11's glory days. These fancy RNAV procedures, that is.

 

Thanks guys!

 

It's possible this feature wasn't needed in the MD-11's glory days.

 

Not necessarily that it wasn't needed, but that it wasn't a consideration.