What Really Happened Aboard Air France 447

[Tallpine]

Thank you. I didn't know that.

Also IAS and TAS are two drastically different things at higher altitudes.

From the simulator work I used to do, I don't think IAS ever gets much more than 250kts 

The pilot/computer has to know which one he/she/it is dealing with.

[Hawkmoon]

Question: Is it technologically possible to use a GPS/GLONASS receiver as a backup tool to estimate the speed of an aircraft?

The pilots had ground speed data. They didn't have airspeed data -- and I don't see how GPS could compute airspeed.

Ah -- I see our resident Airbus jockey already covered that.

[MechAg94]

Airspeed is the speed relative to the air around the aircraft.  So, if you're flying into a strong wind, you might have very good airspeed, but not being going very fast relative to the ground.  (In this case, you'd be well within your flight envelope, even though a GPS would say you are going too slow.)  The amount of air going over the wings dictates lift - and it can't be measured by absolute velocity of the aircraft relative to ground.

Yeah, but I learned watching Under Siege 2 that satellites can detect the wind movements around stealth fighters and see where they are despite radar not detecting them.  If they can do that, the GPS satellites can measure wind speed also.   

Amazing the tech you can learn from movies.   

[MechAg94]

This stuff scares me to death.  It's one thing to automate the control of a turbofan engine, but another to fly a plane.

And like sausage, I've seen how it's made 

Well that is simple.  We just set up all the airliners like drones.  You have your most experienced pilots working shift and flying the planes remotely.  That way your plane gets landed by a veteran pilot all the time no matter where you are including in thunderstorms.   

[Hawkmoon]

Well that is simple.  We just set up all the airliners like drones.  You have your most experienced pilots working shift and flying the planes remotely.  That way your plane gets landed by a veteran pilot all the time no matter where you are including in thunderstorms.   

But Air France 447 wasn't landing.

At least, not intentionally ...

[Tallpine]

Well that is simple.  We just set up all the airliners like drones.  You have your most experienced pilots working shift and flying the planes remotely.  That way your plane gets landed by a veteran pilot all the time no matter where you are including in thunderstorms.   

Nothing can go worng ...

[Fly320s]

Well that is simple.  We just set up all the airliners like drones.  You have your most experienced pilots working shift and flying the planes remotely.  That way your plane gets landed by a veteran pilot all the time no matter where you are including in thunderstorms.   

These are not the drones you're looking for.

[41magsnub]

Well that is simple.  We just set up all the airliners like drones.  You have your most experienced pilots working shift and flying the planes remotely.  That way your plane gets landed by a veteran pilot all the time no matter where you are including in thunderstorms.   

Especially if you want to take a side trip to Iran!

[CNYCacher]

Sure, GPS can't tell you airspeed. And I'm sure that is exactly the reason for the computer being programmed to just give up when there is no airspeed indicator, BUT, let's be realistic here.  What are the chances that your airspeed and ground speed will differ so greatly that you can't pick a nice ground speed somewhere in the middle to keep the plane flying?

So I'll just throw some numbers out that are not accurate because I have no clue about airplanes, but lets just say that you have to be going 100 knots or better to stay flying and 700 knots or slower to keep the wings on.  In the absence of airspeed input, can't the computer shoot for 400 knots ground speed and just hope that the headwind or tailwind is less than 300knots?  Put a disclaimer on the software that says "Not guaranteed to fly the plane through a category 9 hurricane" and you should be good to go.

[Fly320s]

That could work in a pinch, but it isn't worth the progamming and safety effort to make it work as a normal function.

Besides, rules of thumb work just as well. Such as how often 3 comes up:

- 3 to 1 decent profile. A 3 degree decent angle will give a decent rate of 1,000 feet every 3 miles.

- Most jets will fly with power and pitch at 3.  3,000 lbs of fuel flow per hour and 3 degrees pitch up will keep you flying.

[Tallpine]

That could work in a pinch, but it isn't worth the progamming and safety effort to make it work as a normal function.

Besides, rules of thumb work just as well. Such as how often 3 comes up:

- 3 to 1 decent profile. A 3 degree decent angle will give a decent rate of 1,000 feet every 3 miles.

- Most jets will fly with power and pitch at 3.  3,000 lbs of fuel flow per hour and 3 degrees pitch up will keep you flying.

They probably did a safety analysis and decided that in the event of data input failure, the computer would just turn control over to the pilot 


3 degrees pitch up  - that would be angle of attack, not a climb right ?

[Fly320s]

They probably did a safety analysis and decided that in the event of data input failure, the computer would just turn control over to the pilot 


3 degrees pitch up  - that would be angle of attack, not a climb right ?

In planes that show AOA, sure, but most planes don't have an AOA indicator.  Three degrees of nose above the horizon. The combination of pitch and power may create a climb, but it will be slow. More likely, the plane will stay level and accelerate to a safe airspeed.

Of course those numbers might not work with an engine that burns 10k lbs/hr in cruise. 3k might not be enough to stay aloft, but it should be close.

[Tallpine]

In planes that show AOA, sure, but most planes don't have an AOA indicator.

Sorry - back when I was developing simulators, I had to be very careful to discriminate between AOA and pitch relative to the earth's surface.

Can't remember exactly now ... maybe the code computed AOA on the fly (  ) and then fed that value back into the next frame loop to affect rate of climb (+/-), drag, airspeed, etc.  It was sort of recursive, as TAS, ROC, and pitch resolve to AOA, which in turn affects TAS and ROC. 

It wasn't a very sophisticated simulator, as all it was intended to do was serve as a platform to test/calibrate ILS systems in a ground lab.  There was no visual interface except for some instrumentation.  You couldn't do loops or barrel rolls without some variable going negative and producing really bizarre results (I know, because I tried all that) 

[Boomhauer]

hey probably did a safety analysis and decided that in the event of data input failure, the computer would just turn control over to the pilot

Well if the idiot copilot had simply leveled the wings and kept the pitch at a reasonable angle (like the 3 deg Fly320s is discussing above) using the artificial horizon instead of honking back on the stick like a psychotic monkey (or if the captain had been paying attention and knocked the copilot out), AF 477 would have landed...on land.

[KD5NRH]

This does raise an interesting question; does left seat have a quick and easy way to shut down right seat's stick in that particular aircraft?

[roo_ster]

This does raise an interesting question; does left seat have a quick and easy way to shut down right seat's stick in that particular aircraft?

Blow to the temple with the left-seater's fist?

[Fly320s]

This does raise an interesting question; does left seat have a quick and easy way to shut down right seat's stick in that particular aircraft?

Yes.  Both sidesticks have a takeover button. 

[KD5NRH]

Yes.  Both sidesticks have a takeover button. 

Does left have priority if both buttons are being pressed?

A stick position/pressure indicator also seems like a good idea, so that both sides can see what is being done.

[Fly320s]

No, most recently pushed has priority.

I don't see any need for sidestick position indicator.

[Tallpine]

No, most recently pushed has priority.

Stick wars! 


All the math in the 'verse ain't gonna keep this bus in the air.

[Fly320s]

Stick wars! 

Done that in the sim. Things get interesting.

[CNYCacher]

Done that in the sim. Things get interesting.

Define "interesting"?

[dogmush]

Define "interesting"?

Oh God, Oh God, We're all going to die.

[Hawkmoon]

Oh God, Oh God, We're all going to die.

Or, in the case of Air France 447, "Mon Dieu, Mon Dieu, nous sommes tout aller mou .... "

[Fly320s]

Define "interesting"?

Hard to keep control for more than a few seconds, so the plane really has no pilot.