6 ms·
Reminds me of the quote, "For every complex problem there is an answer that is clear, simple, and wrong." -- H.L. Mencken One of the things I have experienced
by ChuckMcM 8y ago
Reminds me of the quote,
"For every complex problem there is an answer that is clear, simple, and wrong." -- H.L. Mencken
One of the things I have experienced in my career is the mind boggling complexity of the software in systems that are capable of killing people. The more people it can kill the more complex the software.
As a result when I read articles like the one posted I find it tantalizing to speculate about the requirements behind the story. Taking the story at face value that Boeing has thought a lot about it and that is how the software has to be, what prevents the other solution of disabling the reverser? My guess is that you want the reverser to work in the event of software failure so it has to always work, but if the pilots pull it while you are flying that would probably rip the engines off the plane. Perhaps the compromise is to take the reverser off during flight and relight the engines using aerial pressure to spin up the engines. (which has me wondering if airlines still have a turbine they can drop down to start an APU which can then be used to start the engines). Which leads me to wondering if the pilots turn off the reverser right away do they have enough residual engine power to relight? Versus when they got to the end of the runway and had nothing? Clearly the 777 doesn't have an APU running when it lands since they would have used that to do an engine start at the end of the runway or if it does, it isn't running.
It is one of those things that my like minded systems friends could sit around lunch and make a good hour and a half discussion out of.
- TremendousJudge 8y agoRelevant article: "Reality has a surprising amount of detail" http://johnsalvatier.org/blog/2017/reality-has-a-surprising-amount-of-detail http://johnsalvatier.org/blog/2017/reality-has-a-surprising-...
- dTal 8y agoThis is very good.
- deleted 8y ago[deleted]
- SomeHacker44 8y agoYes, Boeing still puts the RAT - ram-air turbine - electrical backup system on their planes.
- dullgiulio 8y agoWhy "still"? Even if the chances of a failure of both engines is almost zero, it has happened that there are losses of fuel. The ram-air turbine allows the pilots to have some instrumentation. That's super useful, for example in this accident: https://en.wikipedia.org/wiki/Air_Transat_Flight_236 https://en.wikipedia.org/wiki/Air_Transat_Flight_236
- SomeHacker44 8y ago“Still” because if you read the parent to my reply he uses that term in his query.
- inferiorhuman 8y ago> The ram-air turbine allows the pilots to have some instrumentation. Ideally, yes. I submitted a recent incident where the RAT deployed on a 777 because it's so unusual (and was also not due to lack of fuel): https://news.ycombinator.com/item?id=19039978 https://news.ycombinator.com/item?id=19039978
- salawat 8y agoIf the reverser could rip the engine off the wing, it wouldn't be safe to engage on the ground. Just thought that was worth pointing out. A reverser only redirects thrust, and only generates about 60% of max thrust pushing backwards. It's only on for a limited time on the ground because under a certain speed, you run the risk of blowing FOD into the intake path, putting the engine at risk. I'm not aware of any reason to outright lockout a reverser in flight other than to hedge your bets against a very, very poor set of configuration choices by the pilot (reversing near stall speed too low to recover). I could foresee scenarios where being able to use reversers in the air could save the aircraft with the right combination of subsystem casualties. Not a pilot or engineer, but absolutely LOVE aviation.
- gugagore 8y agoThe cruising airspeed of an airplane is faster than its landing speed. I don't know if that alone is enough to rip the engine off the wing, but it's something that it sounds like you did not consider in making your point. [EDIT remove "roughly speaking an order of magnitude"]
- AshleyGrant 8y ago>The cruising airspeed of an airplane is roughly speaking an order of magnitude faster than its landing speed. No. No it is not. 787 approach speed is 145-153 knots. It does not cruise at 1400+ knots.
- gugagore 8y agoThanks for bringing more precision to the conversation (really). What would you like to call the factor? 3? Call me a weasel, but I was hoping "roughly speaking an order of magnitude" would go down to 3. I suspected it was comfortably above 2. Am I right about that?
- a1369209993 8y ago> I was hoping "roughly speaking an order of magnitude" would go down to 3. I'd call that half a order of magnitude, considering log₁₀(3) is around 0.477. So you're off by more than a factor of two.