Flight 447 air speed, GPS?
February 21st, 2010 | by admin |Many overseas flights have GPS maps showing passengers the speed and flight path on a map. Did Flight 447 note have GPS for speed monitoring and wouldn’t the pilots have GPS in the cockpit? I recently used my hand held Garmin on a domestic flight (window seat) to track route and airspeed.
I thought about this as well since I’ve personally used this technique when I had a pitot freeze up on me. Luckily it was in a small plane at a lower altitude where the wind was not a huge factor. As the others have said the winds at altitude can easily be 200 knots especially in weather. However this doesn’t totally invalidate the ground speed number. When I’m at cruise I make a point of watching the ground speed number to see what the winds are doing since all my fuel planning is based on forecast winds. So if the airspeed indicator craps out I have some "approximate" idea of what my airspeed is. Unfortunately the longer you fly in this condition the less "reliable" the ground speed becomes since the winds change as you fly. In a thunderstorm or near any weather front the winds can change dramatically over a very short distance/time so this technique becomes very minimally usefull but still better than NOTHING. As far as the plane having an FMS/FMC yes it would as well as an ADC (air data computer) that calculates true airspeed and feeds it to the FMS/FMC to give the pilots true airspeed/mach number as well as ground speed and even wind speed/direction (which it calculates based on true airspeed, heading, ground speed and ground track)
4 Responses to “Flight 447 air speed, GPS?”
By Larry454 on Feb 22, 2010 | Reply
George -
Interesting, but remember that GPS does not provide airspeed information, only speed relative to a "static" earth – or ground speed. Winds aloft during storm conditions may exceed 200 knots, either as a tailwind or a headwind. Both conditions, if not understood by the pilots, could cause serious safety of flight issues.
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By Techwing on Feb 22, 2010 | Reply
GPS cannot provide airspeed information. It can only provide speed over the ground, which isn’t the same thing. For flying purposes, the airspeed—the speed at which the air moves past the aircraft as it flies forward—is far more important than speed over the ground. Whenever there is any wind (which is most of the time, especially at high altitudes or in storms), the GPS ground speed may be completely different from the an airplane’s airspeed; even the direction might be completely different.
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By Connor D on Feb 22, 2010 | Reply
You guys are forgetting that this was a large jet. It would be equipped with an FMC/FMS(flight management computer/flight management system). The FMC does not display airspeed. The only place where you would get an indicated speed reading is on the primary flight display.
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By cj1pluspilot on Feb 22, 2010 | Reply
I thought about this as well since I’ve personally used this technique when I had a pitot freeze up on me. Luckily it was in a small plane at a lower altitude where the wind was not a huge factor. As the others have said the winds at altitude can easily be 200 knots especially in weather. However this doesn’t totally invalidate the ground speed number. When I’m at cruise I make a point of watching the ground speed number to see what the winds are doing since all my fuel planning is based on forecast winds. So if the airspeed indicator craps out I have some "approximate" idea of what my airspeed is. Unfortunately the longer you fly in this condition the less "reliable" the ground speed becomes since the winds change as you fly. In a thunderstorm or near any weather front the winds can change dramatically over a very short distance/time so this technique becomes very minimally usefull but still better than NOTHING. As far as the plane having an FMS/FMC yes it would as well as an ADC (air data computer) that calculates true airspeed and feeds it to the FMS/FMC to give the pilots true airspeed/mach number as well as ground speed and even wind speed/direction (which it calculates based on true airspeed, heading, ground speed and ground track)
References :