[nikcub]

the other similar incidents are Birgenair Flight 301, where the pitot tubes were blocked because of insect nests, resulting in pilot confusion:

http://en.wikipedia.org/wiki/Birgenair_Flight_301

and Aeroperu Flight 603, where the pitot tubes had been covered by maintenance workers and not removed prior to takeoff, also resulting in pilot confusion and lack of confidence in instrument readings:

http://en.wikipedia.org/wiki/Aeroper%C3%BA_Flight_603

With these similar incidents you would think that air crews would have learnt from these disasters. If you read the reports on those two accidents, the similarities to the AF disaster are remarkable.

[Simon_M]

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 calculating airspeed.

Is there a reason GPS is not suitable here?

[aperiodic]

GPS gives you speed relative to the ground, not speed relative to the air, which is what's important for aerodynamics.

[eftpotrm]

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]

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.

[crikli]

> You can be moving backwards relative to the ground and still be overspeed

Only in a simulator.

A Cessna 152 is a slow, low-powered trainer. It has a never-exceed speed of 141 knots. So for that aircraft to be going backwards AND be overspeed, you'd have to going into a headwind that exceeded 141 knots.

These windspeeds only occur a) during hurricanes/tornados or b) the high flight levels. You're not going to get a 152 out of the hanger during a hurricane and with a service ceiling around 14,000 feet, you're not getting close to the flight levels, which start at 18,000 feet. I supposed you might see some 100+ knot winds on occasion between 14,000 feet, but again, you're not probably going to be alive to attain the necessary altitude.

[lutorm]

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]

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 :)

[Florin_Andrei]

(asking here because your other reply is nested too deeply)

> The margin between stall and overspeed is something like 20 knots at that altitude.

Whaaa? I thought aircraft have a much wider margin.

How does it change with altitude?

If the margin is so low, then wouldn't a sudden wind gust simply knock the plane off the sky?

[jrockway]

http://en.wikipedia.org/wiki/Coffin_corner_%28aviation%29

(Perhaps a better explanation than the article: http://de.wikipedia.org/wiki/Datei:CoffinCorner.png)

And to answer your question about wind gusts: yes. That is why you don't fly into thunderstorms.

[crikli]

> I'm sure you'd want to have a Big Flashing Warning Light telling you that ground speed <> air speed

That light would never stop flashing. :)

Once you get up a couple of thousand feet, even if the flag is hanging flush against the pole on the ground, you're going to have some type of air movement. The higher you go, the higher the windspeed (in general).

[andrewmccall]

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]

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)

[rwmj]

GPS gives you ground speed. Airspeed is a different thing -- imagine if you're flying into a strong headwind.

[alpyne]

It can't give you the relative speed of the air around the aircraft.

[mtts]

Given the speed at which the readings in my android phone update while driving a car, I'd say yes.

[Shivetya]

let alone we forget losing a B2 bomber during take off for similar reasons.

http://en.wikipedia.org/wiki/Andersen_Air_Force_Base_B-2_acc...

[afterburner]

Yes, I keep hearing about pitot tube problems... I thought the Egypt Air flight I was thinking of had the same problem but I can't find information about it. It might be harder to find because I'm not sure the plane actually crashed.