4 ms·

> Side question: is fly-by-wire an obviously good idea for passenger airplanes? Once you have electric control, you can start putting logic between pilot input

by mopsi 6y ago

> Side question: is fly-by-wire an obviously good idea for passenger airplanes? Once you have electric control, you can start putting logic between pilot inputs and actual control surface movements. You can create dynamic, real-time-conditions-based safety stops that prevent pilots from doing common mistakes like pitching up too much and falling from the sky. With direct control, it's up to pilots to figure out where the limits are and ensure that they are not crossed. With advanced fly-by-wire, pilots can resort to setting goals and it's up to the control system to figure out how far the aircraft can go (within safety limits) to meet them. This is really difficult to get right, but saves lives when it finally works. It's like memory safety in computer programming. If you're really good at programming and you never make mistakes, then you don't need it, but most people make mistakes from time to time and are better off when something checks that their buffers don't overflow and variables don't go uninitialized.

lmm 6y ago
> Once you have electric control, you can start putting logic between pilot inputs and actual control surface movements. You can create dynamic, real-time-conditions-based safety stops that prevent pilots from doing common mistakes like pitching up too much and falling from the sky. Which may end up doing more harm than good, as seen in Air France 447.
- mopsi 6y ago
  Quite the opposite! Protections are built for situations just like the AF447, where pilots have a perfectly flyable aicraft, but crash because they are disoriented, don't understand what's going on, and accidentally push the aircraft out of safe flying margins. The AF447 didn't have automatic protections available due to sensor failure. Flight computers detected the failure and degraded flight controls into direct mode with less protections than under normal operating conditions. While flying on their own, pilots performed below their expected standard and there was not enough information available from sensors for automatic systems to save them.
  - lmm 6y ago
    > The AF447 didn't have automatic protections available due to sensor failure. Flight computers detected the failure and degraded flight controls into direct mode with less protections than under normal operating conditions. Notably the net result was that when the pilots did the right thing (pitching down) and the sensors recovered, a stall warning sounded. > While flying on their own, pilots performed below their expected standard You're talking as though pilot performance is a constant. Notably these pilots had little experience flying "on their own", precisely because of these automated systems, and were thrown in at the deep end, having to take over flying under bad conditions.
    - mopsi 6y ago
      > Notably the net result was that when the pilots did the right thing (pitching down) and the sensors recovered, a stall warning sounded. This is to be expected. Pilots learn on their first single-engine prop trainer that stall horns are primitive mechanical devices based on airflow over the wing and warnings may trigger intermittently when the airflow is seriously disturbed. It's additive: blasting alarm indicates that something is wrong, but lack of warning doesn't mean that everything is right. > were thrown in at the deep end Shallow end. Like stall warnings, airspeed indicators are also known to become unreliable relatively often. It's like loss of cabin pressure, bird strike or a blown tire. Every pilot can reasonably expect it to happen to them, unlike the 737 MAX crashes that took place in completely uncharted territory that nobody knew to be afraid of or prepare for. This makes the official animation at https://www.youtube.com/watch?v=n-hbWO0gL6g https://www.youtube.com/watch?v=n-hbWO0gL6g really puzzling. Speed keeps wildly jumping around throughout the event, an obvious sign that it's faulty. At one point, airspeed indication drops by 200 knots in three seconds to almost zero without any other indications supporting it. Everything else remains consistent. Nose is pitched up and stable. Altitude is dropping fast, vertical speed is negative. Stall warning is blasting, albeit intermittently, and the aircraft is experiencing a characteristic stall buffeting as turbulent airflow develops around wings. Why would any pilot look at that and give a nose up command? It goes opposite to their training and the flying instinct that every pilot should have. If anything, the AF447 case shows that automatic protections should be developed further, to work under wider range of conditions than they currently do. Had some other failure disoriented the crew instead (eg engine failure), and had the protections remained active, they probably would've saved the flight.

by mopsi 6y ago

lmm 6y ago

> Once you have electric control, you can start putting logic between pilot inputs and actual control surface movements. You can create dynamic, real-time-conditions-based safety stops that prevent pilots from doing common mistakes like pitching up too much and falling from the sky. Which may end up doing more harm than good, as seen in Air France 447.

mopsi 6y ago
Quite the opposite! Protections are built for situations just like the AF447, where pilots have a perfectly flyable aicraft, but crash because they are disoriented, don't understand what's going on, and accidentally push the aircraft out of safe flying margins. The AF447 didn't have automatic protections available due to sensor failure. Flight computers detected the failure and degraded flight controls into direct mode with less protections than under normal operating conditions. While flying on their own, pilots performed below their expected standard and there was not enough information available from sensors for automatic systems to save them.
- lmm 6y ago
  > The AF447 didn't have automatic protections available due to sensor failure. Flight computers detected the failure and degraded flight controls into direct mode with less protections than under normal operating conditions. Notably the net result was that when the pilots did the right thing (pitching down) and the sensors recovered, a stall warning sounded. > While flying on their own, pilots performed below their expected standard You're talking as though pilot performance is a constant. Notably these pilots had little experience flying "on their own", precisely because of these automated systems, and were thrown in at the deep end, having to take over flying under bad conditions.
  - mopsi 6y ago
    > Notably the net result was that when the pilots did the right thing (pitching down) and the sensors recovered, a stall warning sounded. This is to be expected. Pilots learn on their first single-engine prop trainer that stall horns are primitive mechanical devices based on airflow over the wing and warnings may trigger intermittently when the airflow is seriously disturbed. It's additive: blasting alarm indicates that something is wrong, but lack of warning doesn't mean that everything is right. > were thrown in at the deep end Shallow end. Like stall warnings, airspeed indicators are also known to become unreliable relatively often. It's like loss of cabin pressure, bird strike or a blown tire. Every pilot can reasonably expect it to happen to them, unlike the 737 MAX crashes that took place in completely uncharted territory that nobody knew to be afraid of or prepare for. This makes the official animation at https://www.youtube.com/watch?v=n-hbWO0gL6g https://www.youtube.com/watch?v=n-hbWO0gL6g really puzzling. Speed keeps wildly jumping around throughout the event, an obvious sign that it's faulty. At one point, airspeed indication drops by 200 knots in three seconds to almost zero without any other indications supporting it. Everything else remains consistent. Nose is pitched up and stable. Altitude is dropping fast, vertical speed is negative. Stall warning is blasting, albeit intermittently, and the aircraft is experiencing a characteristic stall buffeting as turbulent airflow develops around wings. Why would any pilot look at that and give a nose up command? It goes opposite to their training and the flying instinct that every pilot should have. If anything, the AF447 case shows that automatic protections should be developed further, to work under wider range of conditions than they currently do. Had some other failure disoriented the crew instead (eg engine failure), and had the protections remained active, they probably would've saved the flight.