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#1
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Its a 296. It seems the like the higher I go the farther off it is.
I am one to think the GPS would be more accurate than the altimeter. I was thinking that we get incorrect altimeter settings "Casey Wilson" N2310D @ gmail.com wrote in message news:x1Pqe.2896$9a1.185@trnddc01... "Aluckyguess" wrote in message ... I am getting over 500ft. difference and more. "Matt Whiting" wrote in message ... Aluckyguess wrote: How come the GPS reads a different altitude than the Altimeter? For many reasons. The main reason is that they derive altitude by two completely different methods and this inevitably introduces errors. Then each method has its own inherent errors. Even two altimeters side by side won't read the same altitude other than by accident. Matt The number of sattelites being received is one of the variables -- how many are you registering on the GPS? What brand/model is the GPS. Is the GPS certified for navigation? Does the GPS have a Kohlsman equivalent input? What are the altitude specifications of the GPS? Are you comparing it to an altimeter in an airplane? Is the calibration data on the altimeter valid? Have you compared the altimeter to the GPS while parked at a known reference (i.e., the benchmark of your local airport)? My Magellan handheld takes about five mintues of averaging to get a reasonably close altitude correlation -- how much time are you giving yours? Bottom line, forget the GPS altitude reading, dial in the local pressure data into the airplane's altimeter and trust it. |
#2
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Aluckyguess wrote:
Its a 296. It seems the like the higher I go the farther off it is. I am one to think the GPS would be more accurate than the altimeter. I was thinking that we get incorrect altimeter settings The altimeter is only "accurate" when the temperature profile of the airmass is equal to the ISA standard atmosphere. The rest of the time, there will be some error which increases with altitude (wrt wherever the source for the altimeter setting is located). This isn't a concern for en-route operations since everybody's altimeter has the same "error". It can be a concern for terrain clearance in the mountains or in some cases instrument approaches in cold weather since the altimeter reads higher than the plane actually is. |
#3
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Fred G. Black wrote:
This isn't a concern for en-route operations since everybody's altimeter has the same "error". It can be a concern for terrain clearance in the mountains or in some cases instrument approaches in cold weather since the altimeter reads higher than the plane actually is. No concern, either. When IMC, there is a safety margin built into the approaches, and when VMC, there are windows in the copckpit. Pneumatic altimeters are reliable, independant of any infrastructure and work without electricity. Stefan |
#4
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Stefan wrote:
Fred G. Black wrote: This isn't a concern for en-route operations since everybody's altimeter has the same "error". It can be a concern for terrain clearance in the mountains or in some cases instrument approaches in cold weather since the altimeter reads higher than the plane actually is. No concern, either. When IMC, there is a safety margin built into the approaches, and when VMC, there are windows in the copckpit. Pneumatic altimeters are reliable, independant of any infrastructure and work without electricity. Stefan There is a buffer in the procedure design however given that cold temperature corrections are published (at least in Canada, ref CAP GEN p19), it's not unreasonable to assume that there are situations where they should be used. Fred. |
#5
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Fred G. Black wrote:
There is a buffer in the procedure design however given that cold temperature corrections are published (at least in Canada, ref CAP GEN p19), it's not unreasonable to assume that there are situations where they should be used. Of course. That's one more reason why you must pass a test to get the license. Stefan |
#6
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![]() "Stefan" wrote: Pneumatic altimeters are reliable, Most of the time. In very cold weather, you can run into something by relying on a pneumatic altimeter. -- Dan C172RG at BFM |
#7
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Dan Luke wrote:
In very cold weather, you can run into something by relying on a pneumatic altimeter. Pssst, I'll tell you a secret: All that stuff you had to learn to pass the written was somehow linked to real life. Stefan |
#8
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![]() "Stefan" wrote: Pssst, I'll tell you a secret: All that stuff you had to learn to pass the written was somehow linked to real life. Really? Gosh! -- Dan "How can an idiot be a policeman? Answer me that!" - Chief Inspector Dreyfus |
#9
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Does anybody know a quick rule of thumb about how much the altitude changes
with non-standard temperature? I guess is also has to have in consideration that the airport altimeter setting is also kinda "corrected". I.E., you are flying at 4000 ft, then if you set up the altimeter setting for an airport at 3800', you'll be far more accurate than if you set it up for an airport at 1000' (assuming that the atmosphere is exactly the same). or, in other words, the closer you are to the airport altitude, the more accurate your altitude will be. "Dan Luke" wrote in message ... "Stefan" wrote: Pneumatic altimeters are reliable, Most of the time. In very cold weather, you can run into something by relying on a pneumatic altimeter. -- Dan C172RG at BFM |
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