Hey fellows,

i notice, in a guy's video, that he changed the number of the RNP via the FMC, it made me wonder, what do they do? they're on the ND.

 

cheers.

RNP = required navigation performance

 

This is the one you can change. Different kinds of flight segments have different requirements - an approach for instance is going to have much stricter tolerances than enroute cruise. The pilots can key in the proper RNP value if it's not already present in the navdata.

 

ANP = actual navigation performance

 

This is the airplane's own self-check on what the maximum theoretical precision of the navigation system currently is. If ANP gets above RNP, that's a serious situation at night or in IMC because you run the risk that the airplane isn't actually where it thinks it is - you could impact terrain, be way off from the runway at minimums etc.

RNP = required navigation performance

 

This is the one you can change. Different kinds of flight segments have different requirements - an approach for instance is going to have much stricter tolerances than enroute cruise. The pilots can key in the proper RNP value if it's not already present in the navdata.

 

ANP = actual navigation performance

 

This is the airplane's own self-check on what the maximum theoretical precision of the navigation system currently is. If ANP gets above RNP, that's a serious situation at night or in IMC because you run the risk that the airplane isn't actually where it thinks it is - you could impact terrain, be way off from the runway at minimums etc.

that's great!! thanks for the Info Ryan, cheers.

Hey fellows,

i notice, in a guy's video, that he changed the number of the RNP via the FMC, it made me wonder, what do they do? they're on the ND.

 

cheers.

Best example of what Ryan just explained is the LOWI approach. You absolutly need to be on the RNP as per the charts. The NGX handles it great and is well below the Required. But this is an example of where you would never want to be very much off course as there is steep mountains on either side of you. I believe its the second advanced tutorial that takes you through this.

Best example of what Ryan just explained is the LOWI approach. You absolutly need to be on the RNP as per the charts. The NGX handles it great and is well below the Required. But this is an example of where you would never want to be very much off course as there is steep mountains on either side of you. I believe its the second advanced tutorial that takes you through this.

absolutely, cheers.

Best example of what Ryan just explained is the LOWI approach. You absolutly need to be on the RNP as per the charts. The NGX handles it great and is well below the Required. But this is an example of where you would never want to be very much off course as there is steep mountains on either side of you. I believe its the second advanced tutorial that takes you through this.

 

Just to clarify though - the "handling" of the airplane doesn't really have anything to do with ANP - it's not a measure of where the aircraft actually is, it's a measure of how accurately the navigation system can even theoretically know where it is. This is the composite of all the ways the FMC has to judge position - GPS, the IRSes, ground based navaids etc. For a real life example, say you're over the ocean or something and you simultaneously get a drift / map shift in the IRSes combined with a degradation of the GPS signals due to a coronal mass ejection from the sun or something like that. That'd be enough to trigger the warning about not being able to meet RNP.  Where the plane actually is in reality related to the desired route has nothing to do with it - when this situation happens the plane literally can't possibly know with certainty where it is, and that is actually what the issue is.

Just to clarify though - the "handling" of the airplane doesn't really have anything to do with ANP - it's not a measure of where the aircraft actually is, it's a measure of how accurately the navigation system can even theoretically know where it is. This is the composite of all the ways the FMC has to judge position - GPS, the IRSes, ground based navaids etc. For a real life example, say you're over the ocean or something and you simultaneously get a drift / map shift in the IRSes combined with a degradation of the GPS signals due to a coronal mass ejection from the sun or something like that. That'd be enough to trigger the warning about not being able to meet RNP.  Where the plane actually is in reality related to the desired route has nothing to do with it - when this situation happens the plane literally can't possibly know with certainty where it is, and that is actually what the issue is.

that's a great info! thanks for that Ryan! regards.

So, altering the RNP value will make no difference on how the plane flies, right? It will only trigger the warning  if it cannot maintain it?

 

 

It will only trigger the warning  if it cannot maintain it?

 

Correct.

For those interested in learning some more about RNP, here's an article from Boeing about it:

http://www.boeing.com/commercial/aeromagazine/articles/2011_q4/5/

For those interested in learning some more about RNP, here's an article from Boeing about it:

http://www.boeing.com/commercial/aeromagazine/articles/2011_q4/5/

That's great Kyle! thanks for that, cheers.