Bearcat,
Dual GPS that I have used averaged the position and over time, updated the already very accurate inertial position. I expect a new panel mounted dual GPS would just average the two positions and present you with enough nav info to follow the selected tracking. If the position difference of the GPSs was too great it would be another matter and there should be a wealth of experience out there for you to call on.
A question you have not asked, is the actual DOC savings from GPS use. If you have to assume operation in europe, there will be many small direct tracking efficiencies that when added together would slightly reduce DOC. It is the significant direct tracks that can really help and you might only get one of these in a full day of operating.
The tracking distance reduction is not the end of the matter. Your direct track might give a few minutes earlier arrival time that avoids a few times around a holding pattern because of other flights arriving around the same time as your original ETA. If ATC requires passing a certain enroute point at a specific time, your crossing time is more assured with modern navigation gear. Getting something like that wrong is not going to improve the chances of an efficient flight!
Arriving at your destination parking position on time or early usually gives more chance for the subsequent departure to be on time or a little early. There are enough difficulties maintaining a schedule in busy airspace. Every chance should be taken to minimise such difficulties. A good schedule keeping reputation impacts on efficiency. Got to keep those seats filled with happy customers who will go to another operator if your operation is unreliable.
Being late can impact on flight crew duty limitations. If the crew needs an unscheduled rest period where there are no standby crews available, flight has to be cancelled or significantly delayed.
Some of these difficulties can reduced with the accurate navigation available from GPS. From my own experience in Australia, Europe, ME, North Africa and Asia in airline jets (and F27 long ago) the immediate tangible efficiency advantage from modern nav gear can be be about 2%. Your F27 could get about 2%, depending on the routes.
If crew are paid per flying hour, the benefit could be less. My expat crew in one airline could regularly carve 30 minutes flight time from a particular 1 hour 45 minute schedule. We were effectively on a fixed salary. Locals were paid for excess hours. GPS expenditure in your project should therefore be linked to a pilot salary that does not reward greater flight times, meaning the commercial, industrial and operational parts of your project are linked to your avionics part.
Replacing the original nav comms and radar would be based on reliability and maintenance matters and not relate to operational use in the same way as adding GPS.
Thanks, thats helpful. When you say "radar" I assume you mean wether radar? Didn't know the F27 has one? And what's the point in replacing comms? Are the original ones so unreliable/ maintanence-thursty on the F27?
I'm guessing you don't know what's involved in maintaining GPS units? Are they trouble-free for the most part?
Thanks again for the help though, much appreciate it
