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> how does a plane know it's stalling if the pitot tubes are frozen

Angle of attack sensor. AoA is the actual definition of a stall as it measures the point at which airflow breaks away from the wing, reducing lift.

Re your other points on computer warnings, cockpits can get pretty noisy when shit happens with various alarms, buzzers, horns and voices going off. There's actually a tendency to reduce the number of different alarms and use screen information to indicate the problem (although that may be changing after the Qantas drama in 2010 http://en.wikipedia.org/wiki/Qantas_Flight_32).

   There's actually a tendency to reduce
   the number of different alarms and 
   use screen information to indicate the problem

Yes, that'd be good UX. There should be only one actionable task presented at any time to correct errors. In any case, user testing is more important than guidelines.

I wonder if grouped alarms make any sense. For instance you can group all alarms related to stalling together, and present the one thing the pilot can do to correct this. This gives the pilot a sense of what is the most effective use of their attention in a bad situation.

QF mishap - the Wikipedia article didn't talk about the alarms.

With the Qantas incident, they had something like 146 msgs appear on the screen spread over about 5 or 6 pages. So they were forcibly distracted from solving the problem from a top-down approach to having to investigate and cancel each of the 146 msgs, and that was why the two extra pilots were such a godsend, they were able to help out.

Yes, a message flood is also a failure of UX. At my place of work, when a flood of errors occur, we throttle and batch the errors so that the admin doesn't get thousands of emails.

Given that user interfaces on airplanes are digital now, there are a lot of opportunities to innovate.

For instance, where there are multiple failures and alarms, it might be better for the panel to continuously replay the sequence in which the alarms were set off, more or less like how movies do it to help the viewer understand what is happening on the computer. By showing how a system is failing through time, it shows a causal relationship. In addition, you can provide drill down capabilities.

In the case of Air France, perhaps it could have illustrated the AoA through time, and the flight velocity. Perhaps that would have explained something to the pilot.

Messages are prioritized on the screens in the cockpit in any aircraft I've ever seen. Higher priority messages are near the top and are a different color.

There are lots of messages because lots of things can go wrong with an aircraft. They aren't all critical "land now" messages, but may be relevant.

This already happens. I have not been trained to fly an airliner, but I believe that the priority is something like stall, gpws (flying into the ground), tcas (flying into other traffic), master warning, and master caution. These all have their own lights and sounds in the cockpit, and if I know them, so does the flight crew. Presumably the 150 messages that needed to be looked at were all "caution" messages. Too many messages, yes, but nothing that endangered the safety of the flight.

In the AF447 case, the crew was getting the stall warning. They did the exact opposite of what you are supposed to do to recover from the stall. Computers were not the problem. (The same thing happened to that Colgan Air flight a few years ago. The crew reacted to the stall warning by stalling the plane even more. The plane tried to physically force the controls to nose down, which is how you recover from a stall, but the pilots fought it. Bad UI was not the problem. Bad flying was.)

      The plane tried to physically force the
      controls to nose down,

I'm glad you mentioned that. I thought that's what a plane should do at first, and then on second consideration wondered if the psychology of panicking pilots would be to fight the controls in order to wrest the plane from going down.

It does seem like that happens. Wikipedia links to a few incidents involving the stick pusher:

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

Yeah, I don't know about the a/c in question; however, the Colgan crash was a result of the pilot fighting the stick pusher and winning. The stick pusher is not easy to override.

It seems counter intuitive to nose down when you're falling out of the sky, but it's how you recover.

Exactly.

If one were to apply principles of Tao, it would be to yield. Give the stick pusher nothing to push.

I utterly agree on reducing continuous and loud sound warnings in the cabin.

This 1996 757 Aeroperu crash recording is quite scary: http://www.youtube.com/watch?v=G5QSBlYTJ1Y

They had no functioning pitot tubes and lots of contradictory indications, which triggered a storm of alarms, most of them false. Pilots spend quite some time trying to shut alarms off while trying to figure out their situation with air control. I can't imagine trying to talk and cooperate with colleagues, facing a complex system and a life-or-death situation, while so many loud and stressful sounds are buzzing through my ears.

After 9:00, the plane inverts upside down, a "whoop-whoop" alarm goes off and the plane finally crashes into the sea. The alarm only served the sinister purpose of announcing they were going to die.

I really appreciate that recording because it helps empathize with exactly how disturbing it would be to be in that situation.

The autopilot turning off altogether is the biggest equipment problem here (along with averaging/independent sticks). An alarm will surely be necessary but I don't see how killing off autopilot helps since the pilots probably won't have any better of an idea. Perhaps this specific incident caught an ugly edge case.

There is actually a fair amount of ergonomics and interfaces design that goes into these systems - at least equal to Amazon's shopping cart, probably more. Same goes for systems like ATC.

"Stall" does mean "dive now" to every pilot. It is extremely questionable whether including this information explicitly would help at all in the chaotic, confused environment in the cockpit at the time. "Why are you pulling the stick back" is way too long as well, although it does raise a fair point about keeping both pilots aware of each other's control inputs.

Try writing the code for an autopilot some time. It's hard. We spend a lot of time flight testing just the autopilot.

Making something go in a particular direction at a particular altitude at a particular speed is hard enough. Throw in a stall and the best the plane can do is try to nose down.

Well not at 400' and 130knots... That is way they were performing a windshear maneuver ( incorrectly) at FL 340.

Fair enough. My main point is that we spend a lot of time trying to get the autopilot to function right, but it's not an easy problem where you can just throw a bunch of edge case detection code in. There are lots of physical control laws involved in a/c code that you can't break. Silly laws of physics type things.

pitot tubes just measure longitudinally forward airspeed (ie the direction the plane is going). altimeters measure asl (above sea level) altitude, and gyros measure angle of attack and accelerations.

I believe there is a way to tell stall just from altimeter and gyro readings when combined with state information (flap position, gear up/down, &c.) about the plane.

great points about the ui design, though.

i think the biggest issue, though, was the controls not announcing (either through force feedback or a blaring alarm or an urgently blinking light) conflicting input on the control sticks. does anyone know why this is a feature in the first place?

AoA sensors are separate from pitot tubes and in every schematic I have seen located on the exterior of the aircraft, so I believe the measurement is direct.

I double checked, AOA sensors are weather-vane type systems.

> The voice should demonstrate increased tension and panic as counting down.

This part doesn't sound so useful, in a cockpit with worried pilots.

>how does a plane know it's stalling if the pitot tubes are frozen?

I think it can easily do that by measuring the G force similar to an accelerometer on iPhone.

No. There is, not surprisingly, another sensor in the airflow for that.

http://www.lindenhillimports.com/images/photof48.jpg

Accelerometers measure acceleration. You won't feel any unusual G forces for any constant velocity, whether it's climbing or descending.

Yes you're right...Stall is not a free fall but a sudden reduction in lift which can occur for instance when the angle of attack increases beyond a certain value.

It's actually not a sudden reduction in lift either. Even in a stall, lift equals gravity. It's just that the normal relationship between angle of attack and lift is reversed to that higher angle of attack lowers lift rather than increasing it. This makes it inherently unstable and difficult to control, but there is in principle nothing preventing you from flying a stalled airplane all day.