A320F has a latitude limit for alignment of 82 N/S with or without the polar nav mod. And between 60 and 82 it takes significantly extra time.
One of the advantages of the polar nav mod is that it is selected before the boundary of the Mag database area to avoid tripping the AP and ATHR off as the ADIRUs swap from Mag to True automatically as usually they don’t swap in exact sync. Additionally there is a Grid reference on the screen above 65°.
Originally Posted by
DJ Flyboy
Ahh, got you. Any idea of the latitude limitations for the second point? Thanks.
From the Generic A330 FCOM:
The ADIRU gives true heading instead of Magnetic Heading
Above 82°N
Above 73°N between 90°W and 120°W
Above 60°S (make sure you understand that above in the Southern Hemisphere is higher latitudes, ie below on the map!)
Originally Posted by
Sidestick_n_Rudder
IIRC A320 has limitations both for alignment and operation at higher latitudes - don’t have the FCOM at hand to give specific numbers. Anyhow, not possible to operate in Polar regions and use True REF
OTOH A330 has only alignment limitations and has to be used in true ref above certain LAT.
The limitation on the A320 and the A330 are the same if the Polar Nav mod is fitted. Obviously most narrow bodies don't go into the polar region so it's not fitted as standard. A while ago I was told that there was only one narrow body Airbus in existence with the Polar Nav Mod, although with the growth of the LR and CJ narrow body fleet, I imagine that would no longer be true. The operational limits are the same as I quoted above.
Semantics are an issue here- don't mix up the geographic term Polar Regions with the polar regions area as determined by Honeywell et al. If the system is capable to navigate in True up to 82N, then the same is true for up to 82S, but for the IRS manufacturers the Polar Region definition starts at 60S due to magnetic database absence so (legalities aside) you could practically operate in True in the polar region at say 65S. The same logic for that 90W-120W sector.