6 ms·

Considering how many incidents there seems to be due to the loss of these airspeed sensors it seems crazy not to have an additional, different method of calcula

• andrewmccall 15y ago
  GPS can only tell you how fast you're moving over the ground. It can't tell you how fast you're moving through an airmass that might be moving with or against you, this is far more important to keeping a plane in the air than how fast you're moving between point a and point b.
  • al_james 15y ago
    I wonder if GPS could be used to estimate the air speed by means of a permanently refining mathematical model? E.g. If I know I have heading X, ground speed Y, weight Z, thrust A, you should be able to work out your predicted ground speed. Any variation in real ground speed and estimated ground speed is got to me made up of wind direction and velocity right??? Just a thought. (Disclaimer: I know nothing about aerodynamics so this may be nonsense)
• mtts 15y ago
  Given the speed at which the readings in my android phone update while driving a car, I'd say yes.
• alpyne 15y ago
  It can't give you the relative speed of the air around the aircraft.
• aperiodic 15y ago
  GPS gives you speed relative to the ground, not speed relative to the air, which is what's important for aerodynamics.
  • eftpotrm 15y ago
    Yes, but when groundspeed with a slight lag is all that's available is it really that much worse than nothing, which seems to be the failure mode at present? I stress I'm not a pilot and I'm sure you'd want to have a Big Flashing Warning Light telling you that ground speed <> air speed, but there'd seem to be some benefit over nothing at all.
    • jrockway 15y ago
      The ground speed is not useful information. You can be moving backwards relative to the ground and still be overspeed. The only thing that matters to the airframe is the airspeed, and the only way to know the airspeed is to sample the air around the plane.
      • lutorm 15y ago
        You can be moving backwards relative to the ground and still be overspeed. That's not true. The wind even at altitude won't be more than ~100knots. It's true you can't land using GPS speed, but if your GPS tells you 90 knots ground speed at 37000ft, you know something's not right regardless of wind.
        • jrockway 15y ago
          The margin between stall and overspeed is something like 20 knots at that altitude. You're not going to be able to calculate your airspeed from the groundspeed within that margin. (FWIW, I'm pretty sure this GPS speed information is available in the cockpit already. If not, you can get it off your iPhone if you really care.) Finally, the flaps-down speed range of a Cessna 152 is 35-85 kts. So if you're facing into 85kt winds with the flaps down, you're flying backwards and are overspeed. (This can happen with the flaps up too, of course, but winds of 149 kts are a little hard to believe :)
          • lutorm 15y ago
            True about the small margin between stall and overspeed, I didn't mean you could regularly fly like that. But according to the article, their air speed decreased from > 220knots to 90knots. What I meant was that regardless of wind, 90knots air speed should give you a ground speed so low that it should leave no doubt that you are stalled. Apparently the PF was even thinking they were in overspeed at that point. So a ground speed should have told them that they weren't. But on the other hand, positive pitch angle and -10,000 ft/min vertical speed should also tell you beyond a doubt that you are stalled, so the problem here was not that the pilots didn't have the information they needed to figure out what was going on. They did, but failed to process it. It seems this is a classical case of "getting behind the airplane", they were just not processing events at the speed they were happening.
• rwmj 15y ago
  GPS gives you ground speed. Airspeed is a different thing -- imagine if you're flying into a strong headwind.