Far too often I am following a STAR but get all kinds of messages about a descent not being possible or reachable or whatever. You would expect a STAR to be possible, right? What procedure should I follow to make a STAR possible? Slow down sooner? Descent sooner? Both? Use LVL CHG or VS or stick to VNAV...?

 

How come some STARs are so hard to fly?

Do you have a specific STAR that you are referring to?

 

Most STARs should be flyable. If you have a tailwind and you do not enter the forecast winds into the FMC, the aircraft will almost certainly end up above the profile or too fast. You also need to make sure that you have the correct altitude constraints set at the required waypoints.

 

My descents go something like this...

 

Cruise - VNAV, LNAV.

 

Within 10 miles from TOD, I select a lower altitude on the MCP. I will either select <DES NOW> on the FMC for a gradual transition, or I will let the aircraft go directly in to an idle descent when passing TOD.

 

With a cost index of 50 (approx) the aircraft will descend at around 295 KIAS or thereabouts. Below FL100, the aircraft will slow to 240KIAS.

 

Monitor the descent path indicator to ensure that you are remaining on profile.

 

Below 10,000 I will typically use FLCH.

 

220KIAS for the intial approach, clean config. Speedbrake if necessary to remain on profile. Keep an eye on the 'green banana', this will help you to predict the descent.

 

When on intercept heading, 180KIAS with flap 5.

Approaching the G/S, slow to flap 5 manoeuvring speed and select GEAR DOWN, Flap 15.

 

Select landing flap and reduce to VAPP + 5KIAS.

 

The above works fairly well for me.

Sounds like multiple issues. My first suggestion for simmers is the cost index. If it's too high, the system uses an airspeed that would make the descent impossible. Granted, that higher airspeed is maintained through a higher descent angle, but that airspeed still translates to a higher speed across the ground in some way.

 

My second suggestion is to make sure you're entering wind speeds on the DESC FORECAST page. In the States right now, we're seeing some pretty insane wind at altitude. If that is left uncompensated by the system, you're going to be off path when the wind speed changes drastically over the altitudes.

 

Finally, soft constraints (where they give you a block altitude: Above 12000 but below FL210) can make things a little difficult on the system. As such, it will occasionally tell you that the path is unreachable closer to crossing the fix. I've been able to fly the GIBBZ into IAD (it has multiple soft restrictions) with no issue, even though it will occasionally say "nah, not gonna happen." In some cases, I need to pop the spoilers out a little bit, but not by much if I recognize it enough in advance.

One of the nastiest arrivals I've flown is at my base airport LJLJ, the LUMUS 3L followed by transition to ILS 30 approach. In real life, ATC would normaly vector the aircrafts from that point but when I fly offline, executing this approach requires some planning in advance. What I've learned from here is that whenever FMC tells you NO DES PATH AFTER XY, you better check the charts and assess how bad it is, in other words how steep the arrival/transition/approach is. According to that you then reduce the speed at the point where that steep segment starts, to something like 210 or maybe even 190 kts as I usually do on LUMUS 3L. The FMC will calculate the path so you can decelerate normally and when you reach that first point you will be much slower than on normal descends. This is a perfect time to drop out some drag. Flaps to 5, sometimes even 15, gear down (provide huge amount of drag) and if necessary, deploy speed brakes as well (but don't do it with flaps 15 or greater). In case of LUMUS 3L that's the only way I could have achieved the required descend path that is published on the chart. Pretty much the same is BERTA 2L at the same airport. I guess those Alps are good to look at and climb on but I guess planes don't like it that much .

I usually don't worry about it and fall back on the spoilers if I really have to because the descent is really steep.

As mentioned check your cost index, I used to have it around 100 until I realised it was much higher than the the norm and since then descents have been easier to manage. But if the contraints are tightly fixed it might not make any difference.

 

I have also on a couple occasions kept my speed up higher to increase the descent rate and increase drag, only to scrub the excess speed later which helps but you can cut it a tad fine trying that. Or you could could configure yourself early for maximum drag.

 

In the end I don't worry too much about the message as it always seems to work out if you keep a eye on it you use your tools wisely (speed brakes etc). Mostly while staying in NVAV, but I might adjust my turn to final with HDG mode if it looks like LNAV will cut corners and my speed is still high.

Far too often I am following a STAR but get all kinds of messages about a descent not being possible or reachable or whatever. You would expect a STAR to be possible, right? What procedure should I follow to make a STAR possible? Slow down sooner? Descent sooner? Both? Use LVL CHG or VS or stick to VNAV...?

 

How come some STARs are so hard to fly?

What are the messages you're getting? Without the actual message, it's harder to diagnose the problem.

Thanks for the information so far. The next time I will first of all slow down sooner. And I will also note the exact message.

 

If I remember well it was this STAR:

 

https://www.ippc.no/norway_aip/current/AIP/AD/ENZV/EN_AD_2_ENZV_4-25_en.pdf

 

Although I now see it is some sort of GNS STAR...? Anyway, it was assigned to me by ProATC/X.

 

My CI usually is 25 so that can't be the problem, I think. I might do the last flight again to see what happens where!

I remember a situation when not so long ago, approach procedures to runways 18R and 18L to Madrid Barajas changed.

There are mountain ranges north of Madrid and the STAR includes many step descends. When I flew the STAR to 18R for the first time after the changes had been implemented, the aircraft couldn't get down to the desired altitudes. I fly 737 and one of the features of the aircraft is that it is really hard to slow it down and descend at one time even with the spoilers in Flight Detent config. Next time I slowed the aircraft down to 200 kt at the point where I flew 220kt before and it did the work (still with spoiler flight detent however). Sometimes I even slow down to 180 kt and use spoilers, depends on the weather (wind, icing etc).

So one way is to slow down sooner, the other one is to use holding. It is not possible everywhere, but if, according to the published procedures, it is possible to enter holding at the point to which you're not able to descend, you can do that and drop altitude in the hold as well. But the first method is actually more welcomed as it saves fuel and time

Nice! I lived there for a little bit...well, right near there anyway: Hommersåk.

 

Looking at the chart, however, the STAR dumps you off on a fix near the field at an altitude that's appropriate for the approach, so I'm not sure what the issue is. I'll try and fly it tonight and give you an idea of what I did.

These messages and "Unable XXX knots at ABC" crop up fairly often even when the descent has been entered via the NGX FMS, never mind PROATC-X.

 

You are flying the plane: look at the legs and their altitudes & speeds versus the charts. You can't change the fixed altitude restrictions on the charts if you are going to do it properly but there's nothing to stop you evening out the intervening waypoints to avoid abrupt descents or decelerations over short leg distances.

These messages and "Unable XXX knots at ABC" crop up fairly often even when the descent has been entered via the NGX FMS

 

For what it's worth, most of the time, the knots message is because the speed restriction is 250 at 10 (the plane wants to go 240 at that point), or because the speed restriction is over the planned descent speed on the descent page.

 

Change the speed restriction on the descent page to fix issue #1.

Change the descent speed on the descent page to solve issue #2.

 

EDIT (for #1): or, for what it's worth, just delete the speed restriction on the 250/10000 assignment. The controller won't really notice the difference between 250 and 240.

Try to do the ILS Z approach to 18R from SIE IAF with speed of 220kt at SIE. You will see it's not that easy without any, let's say, extraordinary measures like extending gear at 200kt clean configuration Of course keep all the constraints in place - Manco at 9500ft, 14.9DME ILS 7000ft and 10.8DME ILS 5000ft and keep in mind you also need time to extend flaps and decelerate to Vref+5 for final approach so ending at FAP with 200kt is not a particularly good approach:).

Then try to do it with engine de-ice on.

And then with changing winds at different altitudes

 

I wonder why they did change the procedures. Before the current ones, the approach with south wind config went through RBO - no mountains below, a lot less problem.

These messages and "Unable XXX knots at ABC" crop up fairly often even when the descent has been entered via the NGX FMS, never mind PROATC-X.

Sometimes there will be fixes that have a "cross at 250" restriction. If you have the FMC 240 below 10,000' restriction, the FMC will say, "I can't do both. . . "

 

Just saw that Kyle said the same.

In addition to the other suggestions, although the video isn't available the thread should be helpful.

 

http://forum.avsim.n...edbrakes-video/

 

This is the second post from Jack and with another video.

 

http://forum.avsim.n..._hl__video jack

Guys, how about the MOD4 STAR for KSFO, it states that aircraft should expect clearance to cross CEDES intc at 11,000 ft, after that I experience steep descends toward the MEHTA (5000 ft) intc and start of the ILS to rnwys 28L/R? I even followed aircraft on flightaware on that approach Thanks for any clarification!