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FMC RTA feature

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Hi team,The FMC's of the modern airliners I know have a Required Time of Arrival (RTA) feature, where you tell the plane when to get to a fix and it adjusts speed. No FS addons thus far model it. I have no knowledge of programming, but I don't think this should be difficult to simulate. My most humble apologies if I am wrong.Is there any plan for the MD11 or 744 have this feature?ThanksPaul

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Guest alexhn

Modelling this feature would be unnecessary as most Real airlines rarely use the feature as it involves drastic speed changes and is rather inaccurate. Most pilots manually adjust the speed and let the FMC recalculate the estimate for the fix.

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I'll take your word for it...but what makes it inaccurate? If the pilot has to do it manually, wouldn't the speed change be just as drastic? Plus, when using a non-econ speed, wouldn't the FMC calculate the times in the same manner?Paul

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For one, the FMC's wind predictions are just that - predictions. I know it's not unusual for fairly large discrepancies to exist between the predicted winds and what you actually experience up at altitude. This alone is enough to throw off such a feature I think.


Ryan Maziarz
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Guest Steve_Park

>For one, the FMC's wind predictions are just that ->predictions. I know it's not unusual for fairly large>discrepancies to exist between the predicted winds and what>you actually experience up at altitude. This alone is enough>to throw off such a feature I think.Ryan, Not quite...we are in a simulated world, not a real world, with predicted winds. The airdata computers acutally read the wind that are presented to the aircraft and display them on the ND and pg 2 of the PROG function at altitude. As far a predictions, same thing apply's, we are getting the info from some outside weather source, NOAA, SB, AS 6.5, etc and what ever that value is for the altitude we are flying is what we will encounter. The exact data is already there, so implementing the RTA feature seem's rather simple, since we are not dealing with "Predictions".Steve Park

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Just a quick comment about the wind forecast predictions in the real FMCs (at least the ones described in Bulfers). The FMC actually use a mix of the live measured wind data and the predicted data that is in the FMC. It


/Tord Hoppe, Sweden

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>Ryan,>> Not quite...we are in a simulated world, not a real world,>with predicted winds. The airdata computers acutally read the>wind that are presented to the aircraft and display them on>the ND and pg 2 of the PROG function at altitude. As far a>predictions, same thing apply's, we are getting the info from>some outside weather source, NOAA, SB, AS 6.5, etc and what>ever that value is for the altitude we are flying is what we>will encounter. The exact data is already there, so>implementing the RTA feature seem's rather simple, since we>are not dealing with "Predictions".>>Steve ParkI appreciate your sentiments Steve, but Activesky isn't always right...in the real world, the wind isn't always as predicted. The latest activesky has a feature that allows you to account for this uncertainty. They recommend setting it up so that the actual wind matches the predicted wind 80% of the time. That would better simulate the real world, and thus the Active sky wind data becomes more of a prediction than a certainty.I still hope they'll implement the feature anyway...Paul

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Guest D17S

Most of the modern FMSs are using a data link to download updated wind data for preflight setup and then enroute. I'm hoping this feature will be included with the MD11. For instance FSBuild will hook up to AS6 and use realtime or historical enroute wind data to flight plan. This is a nice touch. Of course the FSBuild's FP can be directly loaded into PMDG's FMC, but we still have to hand load in the wind data, waypoint by waypoint. Ugh! If AS6 will hook up to FSBuild, why not our FMC (he asks!). This would be handy for pre-flight setup, but the main bouns would for enroute updates, just like the big boys.Somehow the "sim factor" needs to be addressed. If the FMC winds are loaded correctly so they match the MSFS/AS6 winds environment, then the sim pilot can feel entirely free to take a nap for this flight. Actually, why bother at all! Because this is a sim, the AS6 winds are not just predicting, they are "creating." That means the fuel numbers the PMDG FMC is predicting will come true. The big events in real flights are when the FO jots down the fuel remaining numbers and compares that to the flight plan. I see these all the time, You should see the "bored silly doodles" on these flight plans. But this is the sign of a successful flight. In the real world, we really want these flights to be boring as dirt. However in our sim world, it's even worse. With the fidelity of PMDG's FMC, at TOC if the fuel is looking good then I might as well go to store for another bag of M&Ms . . . then wake me at TOD! We need a "weather failure" feature for the sim . . . something like the mechanical failure feature on the airplane. That variable wind feature in AS6 sounds interesting. If we could get a winds update function to hookup AS6 to the FMC for enroute updates . . . then some capability to randomize some actual winds variation in the sim, that might keep the sim pilot a little closer to the 'puter for those long hauls. I wrote the FSX guys about this. Don't think it made the cut . . but gotta say, that sparkely water sure looks cool. On the RTA front . . . RTA is a CRITICAL function for certain freight companys that are trying to jamb 100 airplanes into a single airport between 1 and 3 am on any given week day. The inbound pilots are actually using that new AIDS-B. That's the new long range, super TCAS that the proposed free flight system will eventually be based on . . . and they are using it RIGHT NOW. Their flight plans are coordinated as well as possible to stagger the arrivals, but those pesky wind variations really play havoc with any kind of a precisely pre-planned arrival time. At 500 miles, these guys start working with each other . . . it

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Guest Steve_Park

>I appreciate your sentiments Steve, but Activesky isn't always>right...in the real world, the wind isn't always as predicted.>>PaulPaul, My point is it does not have to right, wrong, close, etc...what the data gathering program is sending to FS is 100% accurate...if active sky send winds at FL390 are 276@121 kts, then the flight simulator and the FMC see's winds from 276@121 kts....doesn't matter what the real wind's are, this is what the flight sim see's and is all that is necessary for the RTA computation.Steve Park

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>>>I appreciate your sentiments Steve, but Activesky isn't>always>>right...in the real world, the wind isn't always as>predicted.>>>>Paul>>Paul,>> My point is it does not have to right, wrong, close,>etc...what the data gathering program is sending to FS is 100%>accurate...if active sky send winds at FL390 are 276@121 kts,>then the flight simulator and the FMC see's winds from 276@121>kts....doesn't matter what the real wind's are, this is what>the flight sim see's and is all that is necessary for the RTA>computation.>>Steve Park The better question is whether any real world airlines use this feature, and if so, how does it perform in real life compared to the calculations? What if someone does not use a particular weather program? Do developers write multiple codes for each access point for internal MS and third party?Best,Randy J. Smith<<>>


Randy J Smith

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Guest Steve_Park

> The better question is whether any real world airlines use>this feature, and if so, how does it perform in real life>compared to the calculations?>> What if someone does not use a particular weather program? Do>developers write multiple codes for each access point for>internal MS and third party?>>>Best,>Randy J. Smith>><<LCD>>>Randy, A couple of miles up the road from my house are about 500 ATP's that use it daily flying for a rather large freight hauling outfit. Like someone else said, it's how you get a fleet of 100 aircraft into an airport with only 10 stand's within a two hour time frame. You can't rely on ATC getting you out at on time, every time, nor inroute delay's. About the only thing you can control is your speed and why not have the computer do the math, I hear they are good at it :) Your second point does not make sense. It doesn't matter where the weather come's from, a wind is a wind. I use AS 6.5, SB 3.1, FSMeteo 4.7 and MSFS built in Jeppsen real world weather....it does not matter, the wind's are applied to the flight and displayed on the ND and CDU PROGress page 2. They are already using it to compute ground speed anyway, just add an algorithum to compute time to a distant spot.Steve Park

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I also agree that a REALLY nice feature to have would be an ACARS uplink of the WX from activesky...not FSB...it only reads the winds at a single level...let's get the wind right from the (FS) source.

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>>On the RTA front . . . RTA is a CRITICAL function for certain>freight companys that are trying to jamb 100 airplanes into a>single airport between 1 and 3 am on any given week day. The>inbound pilots are actually using that new AIDS-B. That's the>new long range, super TCAS that the proposed free flight>system will eventually be based on . . . and they are using it>RIGHT NOW. >I think you mean ADS-B :)ADS-B isn't really a super TCAS, nor does it replace TCAS. It does give a much longer range traffic view, but only of other ADS-B equipped aircraft. TCAS has the advantage that there are many more transponder equipped aircraft than there are ADS-B equipped. ADS-B can only currently be used in special circumstances, as hinted at above when all the aircraft using an airport at a certain time are from one airline, all equipped to the same standard. Which is why they are able to use it RIGHT NOW.I wouldn't say RTA was critical to this, but it would make things easier.Kevin


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I read awhile back (~6-8 mos) in AW&ST about a European location (Denmark I think) that was testing a datalink between the approach control computer and the aircraft FMC. The goal was to assign a time slot to the arrival where it would be at an approach gate or IAF within 20 sec (my memory again) of scheduled time. The whole idea was to manage the flow enroute and avoid hold stacks or vectors for sequencing.This thread's focus on winds is missing the point, forecasting an ETA is only part of the solution. However, if assigned an ETA then it becomes a real world feature that I believe we will see within next next five years (maybe longer in the US since the FAA progress is measured in decades rather than years).


Dan Downs KCRP

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