Optimum Altitude question

[cappinsuruje2 1]

I know I have not quite started to read the QRH as yet as Im still testing out the NGX..However I do have a question as I am currently cruising at FL360 with a gross weight of 144.8 and cost index of 57. The FMC is reporting Optimum and Max altitudes to be FL378/392. In my mind im thinking that the aircraft should be able to step up to FL380, however it seems like the FMC is thinking differently. Everytime I enter 380 in the step climb line on the FMC it responds with "unable". So hence my need to ask if I am missing something at this point. Any ideas? Gicel Ward

[Tabs 2,790]

How close are you to your T/D?

[cappinsuruje2 1]

Hello Ryan, FMC is reporting 595nm to T/D Gidel Ward

[Jack_C 1]

Should be able to then

[cappinsuruje2 1]

Should be able to then

Exactly what I thought as well. Maybe I stumbled on another issue that needs to be addressed in SP1 Gidel Ward

[cappinsuruje2 1]

Can anyone else confirm this? Gidel Ward

[Cras 6]

I have seen this when I thought a step climb would be in order. I don't think the whole step climb logic in the FMS is working at all correctly at the moment.

[Ruben1123 0]

I have this problem too.However, it must be something we are doing wrong. I'll have to look into it.

[Jigsaw 8]

I didn't have a problem with step climbing when I entered the new flight level on the CRZ page. All I had to do was resetting the altitude hold bug to allow for the new target altitude before entering the flight level or the VNAV mode would disengage with a Check Target Alt message.

[scandinavian13 5,192]

I got an unable last night 300nm+ from T/D, but I just forced it with a CRZ ALT edit and a roll of the MCP ALT.I feel as if I'm doing something incorrectly, as I never bothered to look in the manual to check the proper way to use the function.

[beachdog2001 21]

I have also seen this twice now, very far from TOD, optimum was FL 386 and I was at FL360 and got the Step Unable message.

[namida 0]

Same here every flight I see unable..Usually it displays "NOW" when the aircraft crosses half of setp climb altitude,NGX always say Unable even when I enter the value below optimum altitude.

[NGXfanatic 85]

Just wanted to note that I'm seeing the same behavior reported here, with valid requests for a climb to a new step altitude showing "unable". I think this is very clearly a bug. I have plenty of experience with the other Flight sim NGs, and I feel like I know the FMC inside and out. In fact, during preflight the FMC reported the step climb was valid, telling me when to expect the step climb and showing the fuel savings because of the step climb!!! But the minute I hit the initial cruise altitude was the moment that the step climb prediction changed to unable. I hope PMDG has taken notice of this little glitch.

[willywonka 36]

Whether it's a bug or not, the behavior is repeatable for me: Say for a long flight (where T/D is not within concern), while in preflight or VNAV climb to a cruise altitude less than FMC calculated optimum, entering a STEP altitude will display a step point. However, while monitoring the climb page, as soon as the airplane intercepts the current cruise altitude (N1 changes from CLM to CRZ) the step point becomes UNABLE with saving of 0%, but entering the desired step alt into the FMC CRZ will show correct SAVING calculation. Let me know if you want screenshots or video. It's 100% repeatable.