PMDG 747-400 nav hold

[Guest tskillman89]

I dont know if im doin something wong but when I get done with my FMC input, I go get ready to take off. When I do and im up in the air my nav hold button doesnt want to stay on. I click on it and it will light up for about a second then go off. Sometimes it will stay on though when i press it but 80% of the time it cuts right back off.Need some help on this problem.

[philbrown 9]

Nav hold? Do you mean the LNAV button? Are there any messages on the FMC (something like 'Not on Intercept Heading')?You might have to up-select the next fix to the top to give a direct route between your present position and the next fix, rather than between the runway and the first fix. A screenshot of the ND might be useful.

[craig_read 43]

This sounds to me like a programming issue on your part. Here are some things you might want to look at as causes:1 - Not on an intercept heading to the first track. This basically means you've taken off and the aircraft is not actually on the track and is not currently heading towards the track. By the track I mean the track from the previous to the current active waypoint. Resolution? Steer the aircraft towards the active track, while on and intercept heading try to arm LNAV, you should see it in white on the FMA (on your PFD) indicating it is armed. It will automatically become active once the cross track error (distance from the track) is within 3 to 5 miles.2 - You're using an SID which has a vector portion in it. Some SIDs have 'breaks' in them which account for ATC vectoring from an airfield. You might find LNAV will not activate as you are currently within the portion of the SID where vectoring is controlled by ATC, in which case LNAV has no idea where to go and will not become the active mode.Some pointers, I am not entirely sure why you are arming the LNAV system after takeoff, as a rule, I arm LNAV at the gate before I've even pushed back and the passengers are still boarding. It will sit in white on my FMA now until the aircraft is airborne and over 400 feet AGL. I also arm VNAV at the gate. If there are any major issues with the operation of any of these modes, the FMC will chime and tell you, perhaps UNABLE NEXT ALT when I arm VNAV etc.. informing me that the next altitude target in my plan is unobtainable without modification to performance parameters or relaxing it a little. It's good practice to do this, at the gate set your plan, arm LNAV and VNAV... but DO NOT.. arm your autothrottle system at the gate! This means your TO/GA switches are active and once your engines are running, if you accidentally hit TO?GA you'd get take off thrust, not a good thing while still taxiing I can tell you! Autothrottle to arm goes on as you're lining up.So.. I would check your route, check your SID, look for discontinuities within your plan, does the SID include a break for vectoring? Have a think about how LNAV will pick up the track shortly after takeoff, arm both LNAV and VNAV at the gate and observe and deal with any outstanding issues the FMC has with your plan. This should stand you in good stead for your takeoff and in theory there should be no surprises. I've seen so many simmers make totally unreaslistic plans, first waypoint being direct on runway heading for 7 miles with a hard entered altitude of 10,000 feet entered, you can't expect this aircraft to do that, look at the turns you're asking her to do, look at the climbs, have a think about it, 'is that reasonable?'.. Your issues are definitely within your planning and FMC programming. Screenshots of your ND, PFD, and FMC legs pages and any chimed messages will help diagnose but I am sure with what I've told you here you can probably find the problem.It's all good fun!CheersCraig