Nav accuracy
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Is the Nav Accuracy based entirely on the entry of the coordinates in the FMC at the beginning of the flight? I always get a low accuracy warning at the beginning and then IRS nav only displayed after it aligns and then I never seem to fly on the line. So I’m curious if it all boils down to entering the stand coordinates because I’d figured it would become more accurate the longer I sat on the ground. I know the Maddog and 737 classic use GPS to augment the nav system and I’m assuming we only have IRS with the F100. So is the input of the gate coords the key to accuracy?
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Input at gates is important for sure (because it will otherwise typically default to center of airport), Then it depends on the navaids along your journey to help mantain / enhance accuracy. Degradation is normal, especially in remote areas. But yes, there's no GPS enhancement/Assist
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I've noticed the low accuracy / IRS nav only messages on two different flights, and assumed I had failed to complete something in the pre-flight. But on a subsequent flight, after completing the init pages, including the IRS alignment, I went back to the init pages to check weight... and the *Align IRS was back again. I selected the softkey again, and had no problems. On the next flight, the same thing happened. So I no longer think it was anything I was doing wrong -- something seems to be "unaligning" the IRS while I'm still sitting at the gate.
Edit: And yes, the times I got those FMS messages, I was indeed flying slightly off, but more or less parallel to, the line.
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Initial IRS input is very important for the Fokker and the gate coords have to be accurate. It will degrade if there are no VOR/DMEs in areas. You can remotely tune if you believe you are in range of one to help it regain accuracy.
Without a GPS/GNSS bolted on like models still flying IFR work today. It'll lose its enroute accuracy in remote areas
