| Author | Message | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
I was entertained by this, so I thought I'd share. A couple days ago, I bought a bundled Microsoft GPS receiver and Microsoft Street & Trips 2006. We flew up to Portland Oregon, to give moral support to a friend in the hospital there (he came out ok). It was helpful driving back to the airport, even though some of the turns were given wrong. One in particular listed a left-side exit, when it was really on the right. It's good that I can read maps, and pay attention to street signs. My girlfriend was driving, which made it easy for me to keep up with the pesky navigation tasks. On the flight back, I was wondering if it would handle being in an airplane. Sure thing, it showed us at 33,000 feet at 450mph. While we had it on, the captain came on the PA and said we were cruising at 37,000 feet. Since my receiver was just stuck in a side window, I know I didn't have the best view for satellites. For those that don't know, more satellites make for better calculations. It was entertaining seeing it draw the ground track. | ||
| FAST FRED Rating: N/A |
Sure thing, it showed us at 33,000 feet at 450mph. While we had it on, the captain came on the PA and said we were cruising at 37,000 feet. . The aircraft had a "std day" setting in the Klossermsn window 29.92 , as does EVERY other aircraft. As the barometric pressure will effect the altitude reading , every aircraft sets the altimiter the SAME , to maintain seperation above 18,000ft. The aircraft dont care how far above the ground they are , just how far (1000ft) above or below the other planes. A mid air can ruin your entire day! FAST FRED | ||
| Marc Bourget. Rating: N/A |
It was my understanding, after 9/11, that it was not allowed for a passenger to operate a GPS while in flight! I understand that GPS is a blanket prohibition, not a "during take-off and landing" restriction. | ||
| David Hartley (Drdave)
Rating: N/A |
That's why Garmin makes them for light aircraft and airliners huh? They are not a transmitting device. I seriously doubt an interaction with instruments is really an issue. There are Rules and there is Reality.. We must be somewhere in between? ( I dunno ...) FAA says seat bottoms float and requires it. Plane crashes into water at 300 mph. Who is gonna worry about a flotation seat bottom? | ||
| Brian Elfert
Rating: N/A |
My friend told that the government has programmed the GPS satellites to not provide accurate altitude readings for civilian use. The reason supposedly is so civilians cannot build guided missiles using GPS for guidance. I have not researched this so I don't know if it is true. I do know when going through the Rockies that the GPS reported altitude was varying a lot more than the terrain it seemed. Brian Elfert | ||
| John MC9 Rating: N/A |
I think Marc's assumption is based on the notion that an aircraft passenger can then relay the exact position of that aircraft... To bolster Marc's assumption: "AIRLINE RESPONSE In response to the incidents and government regulations, airlines have taken action to restrict the use of portable electronic devices. Airline policies generally divide PEDs into three categories: those that may never be used, those that may always be used, and those that may be used only at certain times. The treatment of each category of device is, for the most part, very similar among airlines. Airlines generally agree that PEDs such as hearing aids, pacemakers, electronic watches, and one-way pagers may be used at any time during the flight. On the other hand, a majority of airlines do not allow certain portable electronic devices at any time. Examples of these are AM/FM radios, television sets, two-way pagers, and CB radios. In the middle of these two extremes are portable electronic devices that can only be operated before departure, while the aircraft door is open, or after the aircraft has reached an altitude of 10,000 feet. When the aircraft is descending, all PEDs in this category must be turned off. These actions are usually controlled by flight attendant announcements throughout the flight. The PEDs subject to these restrictions include CD players, laptop computers, electronic video games, and GPS navigation sets. As in all cases where PEDs are being used before takeoff or above 10,000 feet, the pilot must be notified that all PEDs have been turned off before departure and/or descent." (From here: The Subcommittee on Aviation People who willingly trade freedom for safety... deserve neither. (Franklin) | ||
| Ross Carlisle (Rrc62)
Rating: N/A |
Brian...That's called differential GPS. It was an intentional timing error introduced by the DOD to limit GPS effectiveness. It essentially created errors of up to 100 meters. They stopped doing this in 2000 or so. With the differential removed, GPS acuracy today is around 10 meters or so. In most cases even a cheap unit will put you within a few feet of your mark. If I recall, the reasoning for doing away with the differential was that it was very costly to maintain a system to limit GPS accuracy, especially when differential GPS recievers could be bought by anyone. Before 2000, you had to buy a differential reciever to get an accurate GPS system. Altitude has never been as accurate as XY position with GPS. Altitude accurace has a lot to do with which satellites you are locked on to and thier position in the sky. While flying, I've seen GPS altitudes that almost match the altimeter and on other occations, altitudes that are thousands of feet off. Most of the time it is pretty accurate. | ||
| Fredd Rating: N/A |
Actually, that was called Selective Availability (SA), and yes it was set to 0, effectively turning it off. Differential GPS is the use of surveyed (i.e. known position) grund based receivers (transmitters in some instances) to improve upon the accuracy of a mobile receiver by removing errors introduced by the ionospheric conditions which cause delays in the signal transmissions. The reason to eliminating SA had more to do with controlling the denial of C/A (i.e. civilian)signals on a local basis during time of war. SA could only be controlled on a global basis. The government has figured out a method to completely deny access to C/A signals on a local basis (e.g. over your favorite hostile arab country, pick one). While uvertical position (altitude) is not as accurate as horizontal (Lat/Lon) position, if you are seeing deviations of thousands of feet between your altimeter and your gps, you either don't have clear sight to the satellites or your altimeter is not working properly. GPS with a proper constllation view will be within about 7-20 meters accuracy (whereas horizontal accuracy is around 5-10 meters) on C/A signals. Variations depend on satellite view, ionospheric conditions, and internal earth model data for the given position. I'd trust the GPS altitude over the baro or radio altimeter, but it's just another tool in the whole scheme of things. | ||
| JW Smythe (Jwsmythe)
Rating: N/A |
Marc, The FAA rules, in contrast to the FAA rules that particular airlines tell you often don't match. I've asked on various flights in the past. Some say "don't do it during takeoff and landing", and some say don't do it. Flight attendants frequently don't have a clue. I flew United a few weeks ago (BTW, bad service, rock hard seats, and the flew me all around the country on a 12 hour flight, because they had an equipment problem and couldn't put me on the 5 hour flight). They had an annoucement after takeoff saying that the FAA rules say passengers could NOT drink alcoholic beverages that they brought on the flight themselves, but we were more than welcome to drink their $5 drinks. I checked the FAA rules. The FAA says no drinks over 140 proof. It makes sense. 151 and everclear are flammable. Fred, the altitude difference may have also been the difference between AGL and ASL, and the way they're measured. I'm rusty on my flight levels. I know there's a few thousand foot seperation between flights in different directions For electronics, I go with logical rules. I know what kind of noise my equipment should be making, and I avoid using anything that should cause problems. I've also read MANY FAA case reports on interference with PED's in aircraft. As it turns out, it's almost impossible for a phone to cause problems on modern aircraft. The worst case that I can think of was a portable game (like a Gameboy, but not specified), that put off weird interference that would kick the autopilot off, and induce a 1 degree bank. Boeing bought the game from the owner, plus bought a dozen others of the same model. It was only that one particular unit that caused problems, none of the other units tested caused problems. Their advice to pilots was, if they notice a problem, try to isolate it to that unit, and try to acquire the unit for testing by the factory. Mythbusters did an interesting episode on the issue. They were testing cell phones. It took a signal generator at a much higher power than a regular cell phone could put off, and it only caused problems with an old radio navigation unit. In a modern aircraft, no matter how much noise they made, they couldn't get anything to tweak out in the least. Really, if cell phones were a big problem, flying over a cell phone tower would be a bigger threat than a cell phone on the plane. I do like the cell phone ban. With the ambient noise on the aircraft (wind, engines, etc), assuming people could even get a signal, they'd be yelling in their phones through the whole flight. All in all, I was entertained that the software was able to show the extreme altitude and speed. I figured it would get confused. Why should it expect that a car can go 450mph at 33k feet.  | ||
| FAST FRED Rating: N/A |
I know there's a few thousand foot seperation between flights in different directions There used to be 2000 ft altitude seperation between aircraft , that was changed a couple of years ago to effectivly doubble the world airspace. With most airlines loosing money , they are basically subsidizing flying , the demand always goes UP for someone elses free money. FAST FRED |