Just a quick Q. on the FMC that someone may be able to answer. I setup my flight plan in the FMC and everything was going fine in VNAV mode except when I went to engage the LNAV. It would not engage (the annunciator light did not come on) when I pressed the button. I looked at the FMC and noticed a message in the cratchpad section that said "Not on Intercept Heading". Now, this must have something to do with why I cannot engage LNAV. So, if anyone has any clues or has experienced this, please tell me what I am doing wrong...LOL!Regards,Tom Stewart

>Just a quick Q. on the FMC that someone may be able to>answer. I setup my flight plan in the FMC and everything was>going fine in VNAV mode except when I went to engage the LNAV.> It would not engage (the annunciator light did not come on)>when I pressed the button. I looked at the FMC and noticed a>message in the cratchpad section that said "Not on Intercept>Heading". Now, this must have something to do with why I>cannot engage LNAV. So, if anyone has any clues or has>experienced this, please tell me what I am doing wrong...LOL!>>Regards,>Tom Stewart >>In order to engage LNAV, the nose of the aircraft must be pointed in a direction that intercepts the active leg of the flight plan.so you need to point your nose at the active waypoint, or at the magenta line before that waypoint, before you engage LNAV.

''Not on intercept Heading''This is displayed when you attempt to engage LNAV but you current track is off course. Go to your MCP manuually select a heading to your next W/P. You will see the track you select as a white dashed line on your HSI map place your track to intercept just before the W/P then re engage LNAV.You can use this when you are asked by ATC to alter course to avoid traffic etc then after they give a resume own navs to bring you back on course.Also if you are flying out on a SID wait until you have your wings level before pressing LNAV. Howard

Thanks for the valuable input gentlemen. I will redo this flight and give those tips a try. BTW Timothy I appeared to be on the magenta line when the VNAV would not engage, but let me try these tips first. I will report back on my results.Thanks again,Tom Stewart

I should of said that the dashed line is magenta not white.Sorry to confuse.

> In order to engage LNAV, the nose of the aircraft must be pointed in a direction that intercepts the active leg of the flight plan. Aircraft must be pointed towards a hdg that intercepts the active leg of the FP.or> Aircraft must be within LNAV engagement limits (L/R)Bruno Francescoli.

Criteria for activating LNAV:Within 3 nm of the magenta line, all headings will engage LNAV.Outside of 3 nm, the current airplane intercept heading must be less than 90 degress(note, intercept heading, not actual heading), and intercept the magenta line before the active waypoint.Failure to meet either criteria will cause a FMC message 'not on intercept heading'Confusing, I know :(

Fred.What you said coresponds to what happend to me. I lost LNav, and could not reengage until I set my heading OFF course by about 30 deg. and then turning back towards the megenta course line at a rather sharp angle. After turning back LNav engaged with no problem.Regards

Thanks again all. I retried that flight using the same flight plan loaded into the FMC and lo and behold the LNAV was captured properly. It must of been that I was outside the 3 nm limit and or the 90 degree intercept of the magenta line. I understand the error of my ways now. Thanks again for all your input here. Regards,Tom Stewart