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joolsd

Are Altitudes sometimes wrong in the SIDS

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I guess this question could apply to any AC which uses a FMC on flight sim. But I am enjoying flying the PMDG at the moment and am unlikley to fly anything else for a very long time.

 

Speaking generally about SIDs from different airports.

Sometimes the altitude on the legs page of SIDs seem different (or contradict) to what the departure chart is saying . For example the plate is saying 2500f or above at 8DME, but in the legs page it says 4000f at 8NMs.

 

Should we be tweaking the altitude, in the legs page?

 

I would like to hand fly the first 2000f more, instead of hitting the A/P, in the past when trying to hand fly, hadn't noticed that the FD was misleading me to climb higher than the SIDs profile?

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I think that a current chart would take precidence over what is programmed into the FMS. The FMS is only as good as the person who entered the data and the age of the AIRAC cycle.

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Most likely a case of the AIRAC cycle in the FMC being out of date compared with the chart you're looking at.

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Most likely a case of the AIRAC cycle in the FMC being out of date compared with the chart you're looking at.

 

The charts at egll or egkk do not change that much. Some times you get a magnetic change of 1 or 2 degrees, but the height seems very, much the same. I think even new nav data can produce this problem. The vertcal profiles always seem wrong. That aside should we tweak the legs page to make it right?

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Yep. Maybe the error happened when the procedure was compiled for PMDG or whatnot. Happens even in real life every so often in fact. Just make sure it is right and correct it by hand if needed.

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8 NM is not the same as 8 DME in your waypoints. If your SID chart has a name for that waypoint then draw a fix round that DME identifier of 8 NM (fix page in your CDU) and check that the dotted ring passes through that waypoint. The same method can be applied if your SID asks you to make a turn at a DME point without a waypoint, this ensures you can check for mistakes before you become aware of it in the air.

 

Sometimes your FMC calculates a turn just before the DME, this is to account for the performance of the aircraft, same applies for fly over waypoints.

 

 

Flightcrew in real life check for discrepancies in the SID/STAR page before departure and to ensure the legs/speed/altitude restrictions match what is on the current chart and to check for changes. The SID STAR can be modified just like your flightplan, you can delete/modify altitude constraints or overfly them on the MCP (altitude intervene whilst on legs page) if ATC or you give clearance to climb.

 

Use navigraph whenver possible for the NGX, you can purchase an FMC cycle software update and full airport charts. Fortunately the navigraph FMC data matches what is on their charts, but may not necessarily apply to real world charts.

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For example the plate is saying 2500f or above at 8DME, but in the legs page it says 4000f at 8NMs.

 

4000ft is above 2500ft.

 

2500ft or above by 8DME = you can indeed fly at 2600ft, or 4000ft, or 950,000,000ft (well probably not the last one... lol) over that position. if it was below 2500ft, then you would need to be at 2500ft, or 2000ft, or 2ft.

 

If (like some departures out of London Heathrow) the altitude was "AT" an altitude, you would need to be exactly at that altitude, not climbing to it or above it or below it.

 

Sometimes the AIRAC will show 240/2500A as the speed/altitude restraint, don't be surprized if the aircraft in VNAV is focusing on the "A" bit of the "or above" part of the constraint and goes higher (above) the listed altitude.

 

That said, AIRAC cycles change, SIDs sometimes change. Navigraph release new updates every 28 days, and if you fall behind (or if the update isn't 100% accurate) then you may find some discrepancies over time.

 

Do be aware though that a LEGS page "D8" waypoint or "8NM" waypoint may not neccicarily be the same as 8DME from a certain VOR or Fix as perscribed in the chart.

 

But just to be sure again as per your quote. 2500 or above does not mean that you need to cross that waypoint at 2500ft, but instead Above that altitude.

 

 

Trent Hopkinson

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Do be aware though that a LEGS page "D8" waypoint or "8NM" waypoint may not neccicarily be the same as 8DME from a certain VOR or Fix as perscribed in the chart.

 

Sometimes it is a ILS DME or it could be a VOR DME.

 

I would imagine if the VOR is displaced it wouldn't be the same as 8NM.

 

 

But just to be sure again as per your quote. 2500 or above does not mean that you need to cross that waypoint at 2500ft, but instead Above that altitude.

 

OK thanks, for the replys

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But just to be sure again as per your quote. 2500 or above does not mean that you need to cross that waypoint at 2500ft, but instead Above that altitude.

 

This is misleading, the 2500ft is the minimum altitude and is totally acceptable for the altitude restraint.

 

Regards.

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I think you should try and stick to the printed profiles.

 

WARNING - STEPED CLIME

Due to interaction with other routes pilots must ensure strict compliannce with the specifided climb profile unless .....etc etc etc.

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There is often many errors with the NAVIGRAPH data for sids and Stars and approaches, either with missing points, incorrect restrictions or out of step points. Its always worth checking what the FMC as come up with compared to what the chart says. Sometimes you may get things like 250/080 and the aircraft wont like it or say its unachievable. It may just require you to change this to 250B/080.

 

A lot of sids have incorrect intial points, or restraints. EGPF is such an example.

 

The comments others have made above are also something to be aware of.

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It may just require you to change this to 250B/080.

 

Can the 737 FMC actually do that? I know that it can do A/B altitude, but speed? Either way current PMDG sidstar format does not allow. Rumor is, PMDG will make way for the 737 to read full ARINC spec data once Aerosoft start putting them out. That would help.

 

 

Sometimes the AIRAC will show 240/2500A as the speed/altitude restraint, don't be surprized if the aircraft in VNAV is focusing on the "A" bit of the "or above" part of the constraint and goes higher (above) the listed altitude.

 

Should still show /2500A instead of /4000 on the CDU though.

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I guess this question could apply to any AC which uses a FMC on flight sim. But I am enjoying flying the PMDG at the moment and am unlikley to fly anything else for a very long time.

 

Speaking generally about SIDs from different airports.

Sometimes the altitude on the legs page of SIDs seem different (or contradict) to what the departure chart is saying . For example the plate is saying 2500f or above at 8DME, but in the legs page it says 4000f at 8NMs.

 

Should we be tweaking the altitude, in the legs page?

 

I would like to hand fly the first 2000f more, instead of hitting the A/P, in the past when trying to hand fly, hadn't noticed that the FD was misleading me to climb higher than the SIDs profile?

 

 

On the legs page it should show 2500 A and not 4000 ft if what the chart is telling you. If the numbers are in capital then the route has either been modified by the FMC or by yourself. If it shows 4000 in non captials then there are no altitude restrictions and the aircraft is climbing according to your econ performance climb settings.

 

As already mentioned you can modify this according to what the plate is asking you to do, so just line select /2500A on the right side of the leg in question. The legs are modifiable and you can easily create a SID by hand from what the chart is telling you.

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Can the 737 FMC actually do that?

 

It can. Have to use it quite frequently, as a matter of fact.

 

 

Oliver Branaschky

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Nice to know, thanks. Never tried it before, I just got used to specific speeds only as format definition allows.

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Nice to know, thanks. Never tried it before, I just got used to specific speeds only as format definition allows.

 

I often get the message "UNABLE 220KTS AT ABCDE", for example, at least flying in Europe. That usually happens when there's a restriction like "220/ABCDE" when the SID says "max. IAS 220". Changing the restriction to "220B/ABCDE" does the trick (of course, it's PMDG after all ;-) )

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On the legs page it should show 2500 A and not 4000 ft if what the chart is telling you. If the numbers are in capital then the route has either been modified by the FMC or by yourself. If it shows 4000 in non captials then there are no altitude restrictions and the aircraft is climbing according to your econ performance climb settings.

 

As already mentioned you can modify this according to what the plate is asking you to do, so just line select /2500A on the right side of the leg in question. The legs are modifiable and you can easily create a SID by hand from what the chart is telling you.

 

Thanks some, interesting learns there.

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Came across this issue few times. Always double check airport charts with what FMC says.

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In real life you ALWAYS check the FMC procedure against the chart - the chart has supremacy and you want to make sure what's in the FMC matches it. (I mention this in both tutorial flights).

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In real life you ALWAYS check the FMC procedure against the chart - the chart has supremacy and you want to make sure what's in the FMC matches it. (I mention this in both tutorial flights).

 

Affirm on that one. ;-)

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Dear Julian,

 

This is perfectly normal, PMDG has simulated the FMC functionality correctly as in the real Boeing 737 NG. The FMC doesn't have all altitudes correct on SIDS and STARS set correctly in the legs page and you have to set the altitude and speed constraints specified on the charts.

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