If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
|
Thread Tools | Display Modes |
#11
|
|||
|
|||
Flight MH370: Altitude issues, flight-recorder operation
On Fri, 04 Apr 2014 10:12:55 -0400, Ho MeGu Y "Ho wrote:
trader_4 wrote: Another thing no one has mentioned. Malaysian military said they had it on radar somewhere over the Straits at 29,500 ft. No one AFAIK has commented on that. That's not a standard altitude. I've monitored the flights I've been on using hand-held GPS, and I can tell you that flight altitudes rarely match up with what the pilots claim to be their cruise altitude or in-flight map display. Being off by 500 feet is common. Don't confuse altitude with "flight level". Above 18,000 feet, everyone switches their altimeters (really a barometer) to standard pressure. That way, they don't have to keep finding out what the barometric pressure is where they happen to be. Remember, all this was in use long before GPS. So one date, flight level 370 (approx 37,000 feet) might be 36,500 while on another day, it might 37,500. Since everyone used the same system, it all works. When the plane gets near an airport, the air traffic controller tells them the local altimeter reading (a four digit number that matches the barometric pressure in inches of mercury without the decimal point). They dial that into their altimeter and can now read altitude in feet rather than "flight levels". |
#12
|
|||
|
|||
Flight MH370: Altitude issues, flight-recorder operation
doesn't really factor in the Malaysian Government lying it's ass off.
On Fri, 04 Apr 2014 12:16:39 -0400, Pat wrote: On Fri, 04 Apr 2014 10:12:55 -0400, Ho MeGu Y "Ho wrote: trader_4 wrote: Another thing no one has mentioned. Malaysian military said they had it on radar somewhere over the Straits at 29,500 ft. No one AFAIK has commented on that. That's not a standard altitude. I've monitored the flights I've been on using hand-held GPS, and I can tell you that flight altitudes rarely match up with what the pilots claim to be their cruise altitude or in-flight map display. Being off by 500 feet is common. Don't confuse altitude with "flight level". Above 18,000 feet, everyone switches their altimeters (really a barometer) to standard pressure. That way, they don't have to keep finding out what the barometric pressure is where they happen to be. Remember, all this was in use long before GPS. So one date, flight level 370 (approx 37,000 feet) might be 36,500 while on another day, it might 37,500. Since everyone used the same system, it all works. When the plane gets near an airport, the air traffic controller tells them the local altimeter reading (a four digit number that matches the barometric pressure in inches of mercury without the decimal point). They dial that into their altimeter and can now read altitude in feet rather than "flight levels". |
#13
|
|||
|
|||
Flight MH370: Altitude issues, flight-recorder operation
Ho MeGu Y wrote:
I've monitored the flights I've been on using hand-held GPS, and I can tell you that flight altitudes rarely match up with what the pilots claim to be their cruise altitude or in-flight map display. Being off by 500 feet is common. Altimeters based on air pressure are not as accurate as consumer GPS. I think you're wrong. Consumer GPS units are not designed to move at 500+ knots. Also, GPS altitude is inherently less accurate than its XY position. Also, there's the Flight Level factor already mentioned by Pat... |
#14
|
|||
|
|||
Flight MH370: Altitude issues, flight-recorder operation
John Weiss wrote:
I've monitored the flights I've been on using hand-held GPS I think you're wrong. Consumer GPS units are not designed to move at 500+ knots. You are wrong. My Garmin Geko has no problems giving altitude, rate of ascent or descent and speed when moving at 500+ mph. I've also had an older Garmin Nuvi (a mapping gps for use in cars) and I think the highest speed that it registered was 950 km/hr (almost 600 mph). Using a newer TomTop 1400 I remember flying into LAX last year and watching it continuously re-calculating the route based on the sparse roads in the desert southwest I was flying over. Also, GPS altitude is inherently less accurate than its XY position. GPS altitude is based on ellipsiodal model of the earth, so the exact verticle position of where sea level is on any given point on the planet will deviate from the elliptical model. When you have a line-of-sight to a significant portion of the sky from the window of a plane that's 6 or 7 miles in the air, your hand-held consumer GPS can make contact with upwards of 12 gps satellites so the altitude accuracy will be, at worst, 50 to 75 feet. Lat/Long accuracy will be 8 to 10 feet - something my Geko can do from a small open field at ground level. |
#15
|
|||
|
|||
Flight MH370: Altitude issues, flight-recorder operation
On 04/04/2014 07:31 PM, H omeG uy wrote:
John Weiss wrote: I've monitored the flights I've been on using hand-held GPS I think you're wrong. Consumer GPS units are not designed to move at 500+ knots. You are wrong. My Garmin Geko has no problems giving altitude, rate of ascent or descent and speed when moving at 500+ mph. I've also had an older Garmin Nuvi (a mapping gps for use in cars) and I think the highest speed that it registered was 950 km/hr (almost 600 mph). Using a newer TomTop 1400 I remember flying into LAX last year and watching it continuously re-calculating the route based on the sparse roads in the desert southwest I was flying over. They should really have something that screams "DEAR GOD WHY WON'T YOU LISTEN TO ME?" if it has to recalculate more often than x per minute. OTOH, my Garmin wanted to send me over a cliff on the edge of a mountain TWICE and the GPS in my phone clocked me skiing at 237.3 mph roughly a mile from any place I could actually have been. Definitely not trustworthy. Also, GPS altitude is inherently less accurate than its XY position. GPS altitude is based on ellipsiodal model of the earth, so the exact verticle position of where sea level is on any given point on the planet will deviate from the elliptical model. When you have a line-of-sight to a significant portion of the sky from the window of a plane that's 6 or 7 miles in the air, your hand-held consumer GPS can make contact with upwards of 12 gps satellites so the altitude accuracy will be, at worst, 50 to 75 feet. Lat/Long accuracy will be 8 to 10 feet - something my Geko can do from a small open field at ground level. -- Cheers, Bev " While in high school, we were encouraged to keep a daily journal. I never liked it, especially when early on I realized that anybody could find it and read it. Fortunately, the jury never saw it." -- Anonymous, for obvious reasons |
|
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Flight MH370 disaster - new theory (asphyxia - air problems) | Home Guy | Air travel | 0 | March 17th, 2014 03:30 PM |
Flight MH370 disaster - new theory (asphyxia - air problems) | Home Guy | Air travel | 7 | March 16th, 2014 10:57 PM |
20 employees of Freescale Semiconductor were on flight MH370 | The Daring Dufas[_2_] | Air travel | 3 | March 16th, 2014 06:42 AM |
Flight MH370 disaster - new theory (asphyxia - air problems) | Home Guy | Air travel | 0 | March 14th, 2014 02:16 AM |