yes I agree there is a huge difference.
But alot of people champion GPS as a 100% reliable system which they can depend on in any wx all the time. When in my experence when it gets horrible and you really need the bloody thing, the atmo conditions are such that there is strong possibility of signal drop.
I was just trying to illustrate that even with the BRNAV IFR GPS which have all the bits and bobs to tell you when its giving you good data. They still loose it occasionally and in my experence its not a rare event. I will admit that the likely error that the units are experencing is far less than the error for those devils devices NDB's
Both those units are certified for GPS approaches in the US.
I am not saying that they arn't great usefull devices. And have done many a IFR leg to intersections using the GPS for track and loosely monitoring the nav with radio nav aids. I just worry that all the chat about them will lull pilots into thinking that the box is god and will never tell a lie. And for the average PPL pilot unless they are very professional in there attitude to flying will tend to go for the easy option and put blind trust in the box. Which could cause a pilot to push on in crap wx when they really should have diverted.
As said on other threads its all about educating the users in the limitations and use of the units. The kit that IO540 has is way out of the league of most UK ppl's. Who after skrimping and saving and watching ebay after xmas may get themselves a very nice moving map colour display. Great but no one explains to them the importance of keeping the database up to date, limitations on using the GPS altitude, the fact that when the wx goes poo thats when you have to watch for signal drop.
BTW out of the 2 units the none graphic trimble is by far the best in my opinion. But its not what people want for VFR flying. In fact both of them are great for what we use it for. But lets face it not much point showing all the controlled airspace or giving warnings that we are in it. We want to be in it as much as possible. So neither of them is a solution for VFR aircraft.
MJ