FMC: No descent path after ....

[bpcw001 22]

Hi, using certain transitions, I get an FMC message saying "No descent path after <insert waypoint here>".I checked for a route discontinuity, but there's none.Also, the altitude and speed restrictions in the transition absolutely make sense and are as found in the charts. I even tried to remove all speed/altitude restrictions except for the restrictions at FAF so the FMC could compute all the way down to the FAF, but still this message shows up. What exactly does that FMC message mean? Where's the problem here? What is the FMC trying to accomplish what apparently cannot be done? Thanks

[Burnspot 5]

Not a pilot, so I'm probably talking out of my a$$ (by not looking it up), but I ran into this yesterday. The descent looked reasonable to me; however, the "No Descent Path..." message appeared while the route itself was not broken. IMHO, I think it comes from a couple of waypoints not having adequate spacing between them for a reasonable descent rate . I got the message after adjusting my route to fit the approach into KRDU for 23L, SBV.FRAZI. I fixed it by looking up the approach in EFB and seeing what waypoint I had deleted. Turns out I had inadvertently deleted a waypoint after the point mentioned in the FMC descent error message. Once I reinserted the waypoint, all returned to normal.

[bpcw001 22]

Not a pilot, so I'm probably talking out of my a$$ (by not looking it up), but I ran into this yesterday. The descent looked reasonable to me; however, the "No Descent Path..." message appeared while the route itself was not broken. IMHO, I think it comes from a couple of waypoints not having adequate spacing between them for a reasonable descent rate . I got the message after adjusting my route to fit the approach into KRDU for 23L, SBV.FRAZI. I fixed it by looking up the approach in EFB and seeing what waypoint I had deleted. Turns out I had inadvertently deleted a waypoint after the point mentioned in the FMC descent error message. Once I reinserted the waypoint, all returned to normal.

Like I said, the transition was right out of the latest Navigraph database and in accordance with the paper charts.If I only knew what the reason for this FMC message is. Without knowing what causes it, I can only do trial and error to resolve the issue.Maybe some PMDG folks or rw-pilots can chime in here.

[falcon999 24]

So how about including the flight plan and/or a few screen shots? Kinda difficult to troubleshoot with no information.

[royski 0]

Experienced the same situation planning the leg from VOBB-VOMM. To remove this message I had to insert the STAR transition and the runway transition resulting to a longer FP. If you would not correct the situation, this message would again appear later on during the flight.

[dts 0]

this appears quite often and seems to be linked to a speed restriction in the STAR, ie 240/4000 for example, remove the speed and the message will go away

[bpcw001 22]

this appears quite often and seems to be linked to a speed restriction in the STAR, ie 240/4000 for example, remove the speed and the message will go away

I actually removed the speed restriction at the FAF itself and it seems to do the trick. No more message showing up.Anyway, glad to hear that I'm not the only one facing this behavior. Just wondering if the real thing behaves like this ...

[Godfrey 0]

I have had the same issue and have dilligently searched for answers in the manuals, but to no avail. As JasonG said above, in the final analysis, it does not cause a problem as the aircraft still decends and meets the limits stipilated. But, I would like to know once and for all, what causes this 'alert' to show up ? Is it some error I am making in the plan with regards to fuel, weight ....., or is this a quirk unique to the 737NGX ? I never experienced this with the PMDG 737NG in FS9.... As a matter of fact, I am going to replicate the exact same flight I last did in FSX when I received that alert, in FS9 right now ! I don't know why I didn't think of doing that before.....It maybe something to do with the navdat info we receive from Navigraph, possibly some changes in the way they process said info to make it available to us. GodfreyG

[masneoquil 66]

You will never experience this on any other Boeing out there for FSX cause none of them had the FMS simulated to this degree.Thant not an issue... to me at least.

[bill1970 0]

I had this message occur when I used a STAR that finished with a VECTORS waypoint. I think the FMC is telling us that it doesn't know what the decent profile from the end of the STAR to the runway (or runway transition) is because vectors implies that the descent will be directed by ATC. As with others, I have ignored the message based on this interpretation. Bill

[Gerardius 20]

Same thing here, "NO DES PATH AFTER D222K", and "UNABLE 250 KTS AT CLE-34" Flight from LEMH to LEBL, LEMH SID = "LUNI2C" (RWY 01L), LEBL STAR = "OSTU1V", TRANSITION "LESBA" (RWY 25R) This is the flight plan: Generated by vroute.info premium 5 LEMH1DIRECT1 N 39.8625 E 4.21861 30201R11 N 39.8534 E 4.21914 272 1302--1000000-1000000 LUNIK2A251 N 40.4397 E 3.39246 0000 SISMO5A251 N 40.6091 E 3.14575 0000 OSTUR2DIRECT1 N 40.7809 E 2.89397 0000 LEBL1-1 N 41.2969 E 2.07833 1425L01 N 41.2922 E 2.10328 8 114--1000000-1000000

[trisager 2]

Same thing here, "NO DES PATH AFTER D222K", and "UNABLE 250 KTS AT CLE-34"

The UNABLE 250 KTS AT CLE-34 is because you are crossing that point at 10,000 feet, and by default there is a 240 kts speed restriction at or below 10,000. Delete the speed at CLE-34, or remove the restriction from the DES page. Not sure where D222K is, so that one I cannot explain. Might be a ripple effect from the speed problem.

[Tabs 2,790]

Here's the technical explanations: NO DES PATH AFTER XXXXX: This message appears whenever satisfying the entered path restrictions requires a descent angle larger than the limit angle. The limit angle is defined as the idle angle at maximum DES speed which is Vmo minus 5 above 10,000 and restriction speed plus 10 below 10,000. What it's telling you is that you're going to be in danger of a reversion to VNAV SPD due to these conditions - it's not telling you that it can't calculate a vertical path or anything like that. Also, if you pass the "global" restriction altitude (10,000 usually) and the FMC detects that you're approaching the +10 limit, it will level out to allow it to decelerate (back to 240 usually) before continuing the descent. The limited DES angle based on speed feature was introduced in FMC Op Program 10.6+. In previous FMC versions the angle values used to trigger the message were 7 degrees above 10,000 and 6 degrees below. Boeing changed this due to pilot complaints where VNAV would constantly disconnect because that was too . VNAV in 10.6+ can't disconnect like this anymore, it just reverts to VNAV SPD. The 737-800 in particular is extremely slippery and hard to slow down and often requires 4:1 or greater when descending, especially if slowing down is also commanded. UNABLE XXX KTS AT XXXXX: The most common way you're going to get this message is by asking the plane to violate a concept known as the "monotonic path" - monotonic essentially means "in one direction" in this context. What this means for the FMC is that it will never do things like descend, climb, then descend again or slow down, speed up and slow down again while in a VNAV PTH descent. It has an expectation that speed and altitude restrictions will always go in the same direction - down. (or up in the case of the climb phase) Gerard, this is very likely the reason you're seeing this with your 250 at CLE-34 restriction - it asks the FMC to violate the standard "global" 240/10000 restriction on the DES page, which always takes precedence over any LEGS page restrictions. You can't break that restriction while in VNAV PTH without changing it or deleting it.All of this is fully modeled in the NGX FMC.

[Cristi_Neagu 134]

Another one in the "it's not a bug, it's a feature" bin.

[Godfrey 0]

Ryan, Thank you for that detailed explanation!! I have just completed reproducing the flight I had this issue with in FSX, with the 737-800wl model in FS9, and received the very same alert. For crying out loud, I was sure something 'cooky' was amiss. Now I understand why as per Ryan's detailed explanation. You guys at PMDG really do take this seriously, don't you ??? Even minute details like these are covered in your products. Why, I believe that if I master this 'bird' I would be able to complete ground school and level-d type training with ease Yeah right, wishful thinking !!! Nevertheless, it is comforting to know that there is an abundance of "real" details in this aircraft. Thanks again Ryan !!! GodfreyG