Hi, kind of a technical question. According to the FCOM, the FMC alert light should illuminate if

• the FAIL light on CDU(s) is illuminated, or

• an alerting message exists for both CDUs, or

• test switch is in position 1 or 2

Now that my navdata is out of date, the message pops up in the FMC and the alert light is illuminated, so far so good. But if let's say drag is required (which I think is shown on both CDU's), it is not illuminated. Or do I remember incorrectly and it is only shown on only 1 CDU?

Maybe someone with a thorough understanding of the system can highlight under which conditions the alert light illuminates and when not?

Thanks,

Robert

Any message that shows on one should show on the other. If you clear the message, Drag Req'd, Steep Descent, Unable 250 etc, it'll disappear from both FMCs.

Hi, kind of a technical question. According to the FCOM, the FMC alert light should illuminate if

• the FAIL light on CDU(s) is illuminated, or

• an alerting message exists for both CDUs, or

• test switch is in position 1 or 2

Now that my navdata is out of date, the message pops up in the FMC and the alert light is illuminated, so far so good. But if let's say drag is required (which I think is shown on both CDU's), it is not illuminated. Or do I remember incorrectly and it is only shown on only 1 CDU?

Maybe someone with a thorough understanding of the system can highlight under which conditions the alert light illuminates and when not?

As you already noticed is the FCOM it's correct that the FMC warning light is amber when an FMC has an alert message or when an FMC fails. The light also comes on when you put the TEST switch in position 1 or 2. This applies for both CDU's, Push the FMC warning light te reset the latch and turn the light off.

Any message that shows on one should show on the other. If you clear the message, Drag Req'd, Steep Descent, Unable 250 etc, it'll disappear from both FMCs.

What does then the second point in the FCOM refer to? Because if the messages are always shown on both, the alert light should be illuminated in all cases, but on my last flight it did not illuminate when the message 'drag required' or 'using altn fuel' appeared - although I can't remember whether it was only shown on the captain's side CDU or both. Robert

Not in all cases only FMC alerts are showing Like The NAVDATA IS OUT OF DATE is an alert, you need to act on it, When the FMC gives advisories FMC alert light is not illuminating, DRAG REQUIRED is a advisory you may act on it., In the FCOM 2 Chapther 11 section 60 you can see what FMC message is a ALERT and what is a ADVISORY.

Not in all cases only FMC alerts are showing Like The NAVDATA IS OUT OF DATE is an alert, you need to act on it, When the FMC gives advisories FMC alert light is not illuminating, DRAG REQUIRED is a advisory you may act on it., In the FCOM 2 Chapther 11 section 60 you can see what FMC message is a ALERT and what is a ADVISORY.

Thanks!