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FMC INOP

Old 26th Jan 2015, 07:37
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Join Date: Jun 2011
Location: Hong Kong
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FMC INOP

Hi there

Can someone please advise whether you are still capable of flying RNAV STARS after the loss of both FMC's in the Boeing. (e.g. Jumbo or 777)

I can't see why not if we are still updating form the GPS but any guidance would be appreciated
Barronflyer is offline  
Old 26th Jan 2015, 07:55
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Join Date: May 2007
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but any guidance would be appreciated
There is the crux of the matter - guidance. The FMC provides the lateral & vertical guidance to fly the STAR. Most of the waypoints are not defined by a radial & DME distance, just a lat & long, so while you could theoretically fly some STARs manually, it wouldn't be very accurate & the workload would be very high. You would also have to ensure you made the altitude constraints manually too. Some seem to struggle with the altitude requirements when they have VNAV, so without it it would be really interesting. The old skills have all but disappeared.

The GPS's only provide input to the FMC position in the Boeings & can't be used for tracking, as the ones in GA aircraft can.
Oakape is offline  
Old 26th Jan 2015, 08:00
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Join Date: Jun 1999
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How would you access the GPS position if the FMC is INOP?
With the FMC inop the GPS can't update anything.

You'd be Alternate Nav and the magenta line on the ND is generated by the ADIRU isn't it? With all it's associated drift/errors.

On the A330 to fly an RNAV Approach you need at least 1 FM working.

( I know you said RNAV STAR.)


Just checked the B777 smart cockpit Navigation section 11.50.1 with regards to Alternate Nav:--

It says the CDU does not accept undefined waypoints or conditional waypoints. Complete departure and arrival proceedures cannot be created in the CDU or cross loaded from the FMC if they contain these waypoints.

Therefore cannot do an RNAV SID/STAR or Arrival without an FMC.

Last edited by ACMS; 26th Jan 2015 at 08:35.
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Old 26th Jan 2015, 09:19
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Join Date: Jun 2014
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I would just sit there and cry.
Amadis of Gaul is offline  
Old 26th Jan 2015, 19:16
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Join Date: May 2000
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It's one of those "legal" vs "able" issues...

As already pointed out, the CDU alone in Alternate Nav is NOT certified for RNP5, so you could not LEGALLY fly an RNAV arrival in normal circumstances.

However, provided the arrival had been entered into the CDU prior to the FMS failure, that route would still be available in the CDU. So, in an EMERGENCY (lost comm, IMC?), you COULD fly that arrival route with nav guidance. You would have to have some confidence in the IRU drift, which you MIGHT get by crosschecking a VOR/DME or ILS/DME fix if available.
Intruder is offline  
Old 26th Jan 2015, 21:57
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Join Date: Jul 1999
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Just invoke your briefed contingency procedures and ask for radar vectors?
Matey is offline  

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