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A330 flight control laws saved Voyager, inquiry finds

flightglobal.com

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Re: A330 flight control laws saved Voyager, inquiry finds

#171

Post by mcguire »

mikeash wrote: post #18
sk5t wrote: post #13

Earlier quoted context omitted.

Thanks for the clarification. Is it normal to refer to kts with the assumption this is related to pressure on the airframe and not actual airspeed? The reference to the 365KIAS rating later in the article provides only a clue IMO.

It literally says "indicated air speed." There's no need for interpretation or assumption. If I saw a raw airspeed without and qualifier, I'd probably assume it meant indicated speed. But I fly small planes where that's the only airspeed available. If you want true airspeed, you have to take what's indicated and convert manually.

IIRC, true airspeed is not especially useful. Ground speed is important for navigation (although hard to get accurately without GPS) and IAS tells you the forces acting on the aircraft.

Re: A330 flight control laws saved Voyager, inquiry finds

#172

Post by swasheck »

nathancahill wrote: post #85
closeparen wrote: post #83

Earlier quoted context omitted.

Is it me or has seat-belt-sign discipline gone out the window? Over my December travels, dozens of passengers on all 4 segments I flew openly flaunted the seat-belt sign, getting up to go to the bathroom and standing in the aisle waiting for it in full view of flight attendants, who didn't say anything. I broke down and did so myself, as the seat belt sign was on for the vast majority of the flight and I was getting…

I've noticed that too. I used to do that myself, until I hit some of the worst turbulence of my life flying in to Denver a couple years ago. Whacked my head pretty hard on main cabin ceiling (the plane dropped ~20ft without warning and I didn't). Ever since then I've worn my seat belt for as much of the flight as possible.

"flying in to Denver ..." I live in Denver and I consistently dread flying home because of the horrid turbulence we experience.

Re: A330 flight control laws saved Voyager, inquiry finds

#173

Post by Arizhel »

JshWright wrote: post #64
sanatgersappa wrote: post #60

Earlier quoted context omitted.

souls. Not bodies.

Not sure if you're serious or not, but 'souls' is the term used to refer to everyone onboard a plane (when declaring an emergency, etc)

Ok, but what do they do for Air Force One? The only souls on that plane when it's flying are likely to be the pilot and copilot.

Same goes for any corporate jets used by corporate executives.

Re: A330 flight control laws saved Voyager, inquiry finds

#174

Post by mcguire »

sk5t wrote: post #23
lutusp wrote: post #10

Earlier quoted context omitted.

The speed of sound varies with altitude. Nevertheless, at 30,000 feet, Mach 1 is 1,091 km/h, so the original statement is not correct (mach 0.9 at 30,000 feet would be about 982 km/h).

My takeaway/learning is that "knots indicated airspeed" is a measure of pressure due to the aircraft mushing its way through the atmosphere, and is vaguely in proportion to actual_airspeed * altitude, and from my non-pilot's perspective ought to be expressed in bars or torr or something else meant for pressure and not velocity or distance.

IAS is calculated from the difference between the outside air pressure as measured by a "static" port on the side of the aircraft and the pressure measured by the pitot tube pointed in (hopefully) the direction of travel. It could be measured as pressure, but it is proportional to true airspeed under standard temperatures and pressures.

The short answer is that bus left about a hundred years ago.

See about page 10-24:

https://www.faa.gov/regulations_policies/handbooks_manuals/a...

Re: A330 flight control laws saved Voyager, inquiry finds

#175

Post by mcguire »

huh333i wrote: post #34
Shivetya wrote: post #3

I do not understand, it took only one input to put it in a dive with auto pilot engaged but two inputs to cancel auto pilot to get it out of the dive?

I have an A320 type so let me try to guess what happened in the A330. The airbus is... different. You can displace the stick 100% in any direction and it wont bank beyond 67 degrees, pitch up more than 30, or pitch down more than 15. It wont overstress because the stick controls G-forces through a closed feedback loop. It also has high-speed protections where it will automatically apply positive G-force to pitch up i…

"...connected sticks in antique Boeing aircraft..."

We saw what you did there.

Re: A330 flight control laws saved Voyager, inquiry finds

#176

Post by FabHK »

JshWright wrote: post #154
FabHK wrote: post #142

Earlier quoted context omitted.

Of course there is a system, and it's sophisticated. Averages are taken in case of inputs on both, and there's a priority button to take precedence (so that the other is ignored). There's more to it than that, but of course there's a system and a lot of thought has gone into it. In the AF 447 case, the left pilot did take priority, but the dude on the right took it back. Had the left one taken it and held it (by keep…

I'm not saying it wasn't thought out, I'm saying that no amount of thought could result in a system that made sense in every situation... Having two independent control inputs means there is always room for subtle failure modes (either technical or operator related). Multi-master is a tricky problem to solve. When it comes to flying a plane, sitting here in my armchair, I think the the simpler solution (linked yokes)…

Fair enough. I tend to agree, in particular as there was not only AF 447, but also the AirAsia from Surabaya to Singapore, Indonesia AirAsia Flight 8501, with basically the same failure mode.

So:

* KISS... but:

* Airbus engineers are certainly aware of it, though... but:

* they have thousands of Airbuses deployed out in the field though with the current tech, so it's unlikely to be changed anytime soon.

Is even more training the answer? Dunno.

My take:

Today's jets are incredibly well designed and safe. If something goes wrong, though, still better to have rather competent crew sitting at the pointy end.

Re: A330 flight control laws saved Voyager, inquiry finds

#177

Post by NamTaf »

lmm wrote: post #116
NamTaf wrote: post #95

Earlier quoted context omitted.

My point was that we don't weigh ourself in 'newtons' despite that being what we are actually measuring. We make some reference conversion to a much more intuitive unit, kilograms. We rely on the fact that it's a pretty constant conversion between the two. Is this really much different than that? I don't think so. The aerodynamics of the plane (stresses on the structure, performance of the aircraft w.r.t. stall, etc.…

The N/Kg conversion might be off by a factor of what, 1% in extreme cases (Denver)? Whereas IAS can easily be a factor of two or more different from the plain English sense of "airspeed".

My point is that airspeed is a vector measured relative to something. In this case, it's set to a specific situation (25C/101.3kPa/0% humidity) and then measured relative to the stagnation pressure at that point because then no matter those variables, the plane reacts more or less the same way for the pilot, who is the one who needs to understand what's happening. Your 'plain English' sense of 'airspeed' is pretty irrelevant to the most critical parts of flight - takeoff, landing and not exceeding the plane's design limits.

Moreover, it also means that if you're flying a very basic plane, you can use external stimuli to understand what the other variables are doing and account for them (also noting that IAS converges to the other 'air speeds', within reason, as you approach the ground). You have markers on runways, wind socks, etc. to all get a feel for what your IAS translates to on the ground and thus how much speed you're going to have when you hit the runway. That seems far more useful to me than having some kPa display on the dash.

Re: A330 flight control laws saved Voyager, inquiry finds

#178

Post by jsmthrowaway »

robzyb wrote: post #82
rwmj wrote: post #4

The link I posted is the only good technical summary, but there are plenty of others about the pilot's ongoing military trial, eg: http://www.telegraph.co.uk/news/2017/02/06/bored-raf-pilot-s... 'Bored' RAF pilot sent 187 passengers into a nosedive 'while playing with his camera'

> The link I posted is the only good technical summary Agreed, except for... > Its automatic high-speed protection system was triggered 3s later, with a maximum indicated air speed of 358kt (662km/h), or Mach 0.9, recorded.

There is another thread on exactly what you've perceived as an error, because that statement is, in fact, accurate, counterintuitive to a physics education.

Re: A330 flight control laws saved Voyager, inquiry finds

#179

Post by drewkett »

brandmeyer wrote: post #165
drewkett wrote: post #81

Earlier quoted context omitted.

Just so you know the forces are actually proportional to the square of equivalent airspeed which is indicated airspeed adjusted for the compressibility of the air at the sensor. Indicated airspeed is still a better number than true airspeed for approximating the aero forces

So long as we are being pedantic: The sensor just reads dynamic pressure. To get IAS from the pressure signal it is sufficient to solve the equation dynamic_pressure = density * indicated_airspeed^2, where density is taken to be air at a reference temperature at sea level (mumble mumble except for transonic and supersonic conditions mumble). In order to compute true airspeed, you need to measure the absolute pressure…

FYI

  dynamic_pressure = 0.5 * ref_density * equivalent_airspeed^2
Its not a function of indicated airspeed. Indicated airspeed needs to be corrected for the compressibility of air to obtain the equivalent airspeed. At low airspeeds/altitudes, the indicated airspeed and equivalent airspeed are very close, so your equation would hold up just fine.

As a result at higher altitudes and faster speeds, the red line on an indicated airspeed gauge would be variable to account for the effects of compressibility.

Re: A330 flight control laws saved Voyager, inquiry finds

#180

Post by [deleted] »

awinter-py wrote: post #160
Xixi wrote: post #137

Earlier quoted context omitted.

All modern Boeings (>= B777) are FBW (fly by wire) and have flight envelope protection. A 787 will absolutely not go over-speed: it will automatically throttle back.

Will throttling back help? The plane is pitched down 18 degrees and mach 0.9 KIAS.

[deleted]
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