Inspired by #1075: Ask an Airline Pilot

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Re: Inspired by #1075: Ask an Airline Pilot

Postby dubsola » Thu Jul 05, 2012 12:23 pm UTC

On the inside or the outside?

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Re: Inspired by #1075: Ask an Airline Pilot

Postby wam » Thu Jul 05, 2012 1:01 pm UTC

dubsola wrote:On the inside or the outside?

Iv only seen it on the outside, but i imgaine both.
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Re: Inspired by #1075: Ask an Airline Pilot

Postby KodiakRS » Thu Jul 05, 2012 5:23 pm UTC

Steax wrote:So basically a floppy wall thing isn't any harm, right? There was a moment in my childhood when planes got scarier as I realized that, yes, there are only a few inches between me and the sky.

Also, on the accident avoidance side: are there any signs that passengers should be aware of that might indicate that something's wrong? I often hear different whistles or hums on planes, but I expect that to be because of differences of seating, weather and plane models. Still, it's nice to know if there are clear indicators that passengers should report about.


Not really. Airplanes all have their little quirks and noises that can seem disturbing. The a320 family of aircraft is famous for it's hydraulic power transfer unit that makes a noise like a dog barking the cargohold. I don't think I've ever heard an md-80 retract or extend it's gear in a way that didn't involve some combination of thinking, shuddering, or groaning. There's a type of airplane I fly on a lot where de-ice fluid pools in a certain spot and then streams out above a certain speed looking a LOT like a fluid leak.

Chances are that the pilot are going to know about something long before you do anyway.

A floppy wall is basically a non issue. The wall that you can see from inside the airplane is there for looks and to protect the insulation/wiring that runs along the aircraft. On a somewhat related note, there have been multiple cases of aircraft loosing large chunks of their outer skin and continuing to fly.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby EdgarJPublius » Thu Jul 05, 2012 6:12 pm UTC

wam wrote:
Steax wrote:I do find the cell phone thing to be oddly strange, though, because a great deal of people who know about planes are waaaay over in the "they're actually fine" or "holy shit turn that off or we're gonna die" camp. It's an interesting thing to talk about.


Also when you install new electronic components in the cockpit you have to do electronic emissions tests, to check that everything works.


My understanding is that this is actually the biggest barrier to allowing cell-phones on planes. Since to allow it there would have to be an extensive emissions/interference certification process for just about every different kind of phone on every different kind of airplane.


I don't think I've ever heard an md-80 retract or extend it's gear in a way that didn't involve some combination of thinking, shuddering, or groaning.


I don't think I've ever experienced an MD-80 do anything that wasn't at least mildly terrifying. It probably has something to do with the ridiculous seating configuration.
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Re: Inspired by #1075: Ask an Airline Pilot

Postby KodiakRS » Thu Jul 05, 2012 6:35 pm UTC

EdgarJPublius wrote:I don't think I've ever experienced an MD-80 do anything that wasn't at least mildly terrifying. It probably has something to do with the ridiculous seating configuration.


Have you ever sat in jumpseat on an MD80 and watched the crew? They used about 8 different timers during each engine start, the cockpit layout looks like it was designed by a guy with a square dartboard and a dart for every switch or button, and the controls require so much movement it looks like the pilot flying is boxing with the airplane instead of flying it.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby MichiK » Thu Jul 05, 2012 11:44 pm UTC

KodiakRS wrote:Have you ever sat in jumpseat on an MD80 and watched the crew? They used about 8 different timers during each engine start, the cockpit layout looks like it was designed by a guy with a square dartboard and a dart for every switch or button, and the controls require so much movement it looks like the pilot flying is boxing with the airplane instead of flying it.


Oh yeah, the good old MD80. Back in the late 90ies, I was sitting on passenger seat 1C, what came pretty close to a jumpseat as there was no cockpit door at all (hardly imaginable after all the FUD following 9/11...) but just some curtain that stayed open all the time. It was quite some fun to watch the guys in the cockpit, especially since on another flight a few weeks before I had the pleasure to visit an Airbus cockpit. That was like worlds colliding...

Since the AF 447 crash is in the media again now, what's the status quo about GPS in airliners? I remember that there were plans to use it since it's a lot more convenient and less error-prone than radionavigation (at least on the user's side, not technically per-se) and does not have the flaws of inertial navigation like considerable offsets after long flights over the ocean. Why the question: If there was a GPS receiver on board, then it should not have been too difficult for a somewhat sophisticated FMS to easily detect the problem that lead to the AF 447 crash, shouldn't it? Or would problems like that already be detected but the warning message (if there is any) would just confuse the pilots even more since they have never seen it before and it looks really obscure?

(Short version of the context for everyone interested: AF 447 presumably crashed because the pitot tubes froze and gave a wrong airspeed indication which was misinterpreted by the crew and/or the computers and basically lead to a stall at cruising altitude, causing the plane to drop into the ocean like a stone.)

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Re: Inspired by #1075: Ask an Airline Pilot

Postby KodiakRS » Fri Jul 06, 2012 2:41 am UTC

MichiK wrote:
KodiakRS wrote:Have you ever sat in jumpseat on an MD80 and watched the crew? They used about 8 different timers during each engine start, the cockpit layout looks like it was designed by a guy with a square dartboard and a dart for every switch or button, and the controls require so much movement it looks like the pilot flying is boxing with the airplane instead of flying it.


Oh yeah, the good old MD80. Back in the late 90ies, I was sitting on passenger seat 1C, what came pretty close to a jumpseat as there was no cockpit door at all (hardly imaginable after all the FUD following 9/11...) but just some curtain that stayed open all the time. It was quite some fun to watch the guys in the cockpit, especially since on another flight a few weeks before I had the pleasure to visit an Airbus cockpit. That was like worlds colliding...

Since the AF 447 crash is in the media again now, what's the status quo about GPS in airliners? I remember that there were plans to use it since it's a lot more convenient and less error-prone than radionavigation (at least on the user's side, not technically per-se) and does not have the flaws of inertial navigation like considerable offsets after long flights over the ocean. Why the question: If there was a GPS receiver on board, then it should not have been too difficult for a somewhat sophisticated FMS to easily detect the problem that lead to the AF 447 crash, shouldn't it? Or would problems like that already be detected but the warning message (if there is any) would just confuse the pilots even more since they have never seen it before and it looks really obscure?

(Short version of the context for everyone interested: AF 447 presumably crashed because the pitot tubes froze and gave a wrong airspeed indication which was misinterpreted by the crew and/or the computers and basically lead to a stall at cruising altitude, causing the plane to drop into the ocean like a stone.)


I would imagine that af 447 not only had multiple GPS receivers but they were in fact the primary means of navigation, the inertial nav system serving only as a backup. I'm not sure how you think GPS could have prevented the accident from happening. The only speed readout that a GPS can produce is your speed over the ground which can vary by hundreds of knots depending on the wind and your true airspeed. I suppose the crew could have looked at their ground speed and just held the speed relatively constant, but they would have had to make a note of their baseline ground speed BEFORE the instrumentation failure and the speed would be inaccurate as soon as the winds changed.

By the way, AF447 is a perfect example of why I don't like airbus's design philosophy. Not only did you have a triple instrumentation failure on a system where a single failure is a big-ish issue, but the information provided to the crew was so baffling that they rode the stall all the way into the ocean from 30,000+ feet. This wasn't a gut reaction in the wrong direction like colgon 3407, this was an experienced crew who had no clue what sort of situation they were in.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby MichiK » Fri Jul 06, 2012 9:01 am UTC

KodiakRS wrote:I would imagine that af 447 not only had multiple GPS receivers but they were in fact the primary means of navigation, the inertial nav system serving only as a backup. I'm not sure how you think GPS could have prevented the accident from happening. The only speed readout that a GPS can produce is your speed over the ground which can vary by hundreds of knots depending on the wind and your true airspeed. I suppose the crew could have looked at their ground speed and just held the speed relatively constant, but they would have had to make a note of their baseline ground speed BEFORE the instrumentation failure and the speed would be inaccurate as soon as the winds changed.

Of course, the wind in higher altitudes can be quite strong and ground speed can differ from air speed a lot. However, aren't the winds in higher altitudes also quite constant? As a non-expert I would think that it should be at least possible to detect that the IAS is flawed by comparing the speeds... on the other hand, you wouldn't even need the ground speed for that, testing the combination of IAS, engine parameters and altitude should give a clear answer... and specifically a stall could be detected by the AOA alone (hopefully early enough before it's too late).

KodiakRS wrote:By the way, AF447 is a perfect example of why I don't like airbus's design philosophy. Not only did you have a triple instrumentation failure on a system where a single failure is a big-ish issue, but the information provided to the crew was so baffling that they rode the stall all the way into the ocean from 30,000+ feet. This wasn't a gut reaction in the wrong direction like colgon 3407, this was an experienced crew who had no clue what sort of situation they were in.

What I'm always sceptical about considering Airbus (and fly-by-wire, drive-by-wire etc. in general) is that you give the computer control over everything and completely give up the physical connection between the controls in the cockpit and the rudders themselves. While the computer can interpret the input and do what the pilots really want instead what just they put in and while it can prevent dangerous maneuvres leading into possibly unrecoverable states, this can lead to disaster when the computer is wrong about the real situation the plane is in and assumes something different. In that case, the computer might even prevent the pilot from doing what is neccessary to save the situation.

In earlier times, an able and experienced pilot could always say "screw the instruments, I think they're lying" and just rely on his own senses knowing that the plane would always do exactly what he tells it to do. In a modern glass cockpit with computers everywhere, when the system hits a situation the programmers have never thought of, you can just sit and watch, even if you actually know what's going on...

Another thing is the ever growing complexity. There is so much data read and processed at every second, which is invisible most of the time. But when the shit hits the fan, the computer will just put some fancy error message on the monitor and confront the pilots with all of that. This will of cause even worsen the situation if some of the data are flawed without the computer noticing.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby gorcee » Fri Jul 06, 2012 3:10 pm UTC

MichiK wrote:What I'm always sceptical about considering Airbus (and fly-by-wire, drive-by-wire etc. in general) is that you give the computer control over everything and completely give up the physical connection between the controls in the cockpit and the rudders themselves. While the computer can interpret the input and do what the pilots really want instead what just they put in and while it can prevent dangerous maneuvres leading into possibly unrecoverable states, this can lead to disaster when the computer is wrong about the real situation the plane is in and assumes something different. In that case, the computer might even prevent the pilot from doing what is neccessary to save the situation.

In earlier times, an able and experienced pilot could always say "screw the instruments, I think they're lying" and just rely on his own senses knowing that the plane would always do exactly what he tells it to do. In a modern glass cockpit with computers everywhere, when the system hits a situation the programmers have never thought of, you can just sit and watch, even if you actually know what's going on...

Another thing is the ever growing complexity. There is so much data read and processed at every second, which is invisible most of the time. But when the shit hits the fan, the computer will just put some fancy error message on the monitor and confront the pilots with all of that. This will of cause even worsen the situation if some of the data are flawed without the computer noticing.


There's like, an entire industry dedicated to automatic detection of these types of issues. The problem isn't that the control system is computerized; it's that they never really finished the job and put in proper FDI (fault detection and isolation) algorithms and the like. Constrained Kalman Filters have been around for years, and are very adept at detecting these types of problems.

Far more airplanes have crashed due to human error vs. flight control error. I agree that the pilots need to be kept in the loop, but the V&V process for these algorithms is very slow, and needs to be accelerated. AF 447 could have been entirely prevented just by using a few algorithms that are sitting here on my computer.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby Роберт » Fri Jul 06, 2012 6:14 pm UTC

KodiakRS wrote: This wasn't a gut reaction in the wrong direction like colgon 3407,

Colgon 3407 is on of many reasons why I'm less scared about compute control systems than I would be otherwise. That crash could have been avoided if the pilot had allowed the automatic control to do it's thing. But he overrode it and when against its safety response, making the plane never recover from the stall.

Yes, we need to be very careful about systems like that, but really, they can be tested to be VERY reliable. Just like I'd actually trust a computer to be better at math than a human, I'm not sure that the modern control systems are any less reliable than human judgment.

AF 447 sounds really unfortunate, though. It sounds like it really wasn't the crew's fault in that case. Would the pilot have been able to fix it if he'd taken control from the co-pilots? Doubtful. It seems unlikely he was able to interpret what was happening and yet didn't do anything about it.
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Re: Inspired by #1075: Ask an Airline Pilot

Postby Steax » Mon Jul 09, 2012 5:38 am UTC

I have a new, but related, question. Can you use Bluetooth on planes? I've actually used it several times, and only just realized that it's probably classified like other radio-using devices...
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Re: Inspired by #1075: Ask an Airline Pilot

Postby Adacore » Mon Jul 09, 2012 6:37 am UTC

I'm pretty sure bluetooth isn't allowed - it's certainly deactivated on my phone when I switch it into flight safe mode.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby tastelikecoke » Thu Jul 12, 2012 9:07 am UTC

Aren't magnetic compasses already distorted by degrees due to pole shifting? Is the pole shift compensated? The cellphones would probably have littler chance than a sudden pole reversal.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby wam » Thu Jul 12, 2012 10:35 am UTC

tastelikecoke wrote:Aren't magnetic compasses already distorted by degrees due to pole shifting? Is the pole shift compensated? The cellphones would probably have littler chance than a sudden pole reversal.


Well assuming aircraft navigation is the same a boat navigation. Yes for a short answer.

In more detail, when navigating you have two different compass courses. You have true, which is the course read straight of the chart. You then have magnetic which is the true with the variation factor applied. You then steer to magnetic and plot it as true if that makes sense. Now practically for most applications (everything other than aviation I'm guessing) you can normally ignore it as in the UK at the moment its only about 2 degrees and normally there are larger sources of error.
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Re: Inspired by #1075: Ask an Airline Pilot

Postby gorcee » Thu Jul 12, 2012 3:18 pm UTC

wam wrote:
tastelikecoke wrote:Aren't magnetic compasses already distorted by degrees due to pole shifting? Is the pole shift compensated? The cellphones would probably have littler chance than a sudden pole reversal.


Well assuming aircraft navigation is the same a boat navigation. Yes for a short answer.


It is. My most recent FAA Pilot Training manual dates back to I think 1975*, but it had charts for compensating for that. I'd imagine more recent manuals would have similar charts, as magnets have not gone through major introspective life-altering changes in the last 40 years.

(It also had some things that are horribly, horribly wrong. Like, the description of how a wing works was some bastardized cross between the incorrect Venturi explanation and the incorrect greater transit explanation. It made me weep.)

*1975 pre-dates me, and I am not a pilot, although I have some training hours under my belt. The manual was something I picked up as a collector's item, since I am in some aspects an aeronautical engineer.

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Re: Inspired by #1075: Ask an Airline Pilot

Postby eSOANEM » Tue Jul 17, 2012 10:44 pm UTC

wam wrote:
tastelikecoke wrote:Aren't magnetic compasses already distorted by degrees due to pole shifting? Is the pole shift compensated? The cellphones would probably have littler chance than a sudden pole reversal.


Well assuming aircraft navigation is the same a boat navigation. Yes for a short answer.

In more detail, when navigating you have two different compass courses. You have true, which is the course read straight of the chart. You then have magnetic which is the true with the variation factor applied. You then steer to magnetic and plot it as true if that makes sense. Now practically for most applications (everything other than aviation I'm guessing) you can normally ignore it as in the UK at the moment its only about 2 degrees and normally there are larger sources of error.


It's also worth noting that this difference (variation) is not due to pole shifting but rather due to the magnetic and true north poles not being in the same place, pole shifting leads to the variation changing by something like about 0.3 degrees a year IIRC in the south of England.
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