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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

#21

Post by sk5t »

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.

So it does. I still find this disunion of UOM disagreeable, in the way that "in thousandths, take 300 grams of acetaminophen twice daily" is troubling.

Re: A330 flight control laws saved Voyager, inquiry finds

#22

Post by djrogers »

mikeash wrote: post #9
sk5t wrote: post #5

> with a maximum indicated air speed of 358kt (662km/h), or Mach 0.9, recorded What? 358 knots is much closer to mach 0.5 in air. 358 meters/second is close... 662 mph is close.

Indicated airspeed is based on the force of the oncoming air, and decreases as air gets less dense. There's some altitude where 358kt indicated is Mach 0.9. Edit: before I get more replies attempting to lecture me on how wrong I am, please look up the difference between true airspeed (how fast the air is moving past the airplane) and indicated airspeed (a measurement derived from the difference between static and dyn…

That's not correct. At 33,00 ft, Mach 0.9 is about 600Kts, the altitude charts don't go high enough for Mach 0.9 to be 358Kts - by that point yo haven't enough air to transmit sound.

And if you're implying that 358kts indicated could be 600kts actual with the right tailwind - that's true, but it still wouldn't be Mach 0.9, as the speed of sound applies only to airflow over the airplane. No matter the tailwind, the airflow will remain subsonic.

If this weren't the case, passenger liners could go supersonic with a 200kt tailwind all day long...

Re: A330 flight control laws saved Voyager, inquiry finds

#23

Post by sk5t »

lutusp wrote: post #10
sk5t wrote: post #5

> with a maximum indicated air speed of 358kt (662km/h), or Mach 0.9, recorded What? 358 knots is much closer to mach 0.5 in air. 358 meters/second is close... 662 mph is close.

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.

Re: A330 flight control laws saved Voyager, inquiry finds

#24

Post by huh333i »

lutusp wrote: post #10
sk5t wrote: post #5

> with a maximum indicated air speed of 358kt (662km/h), or Mach 0.9, recorded What? 358 knots is much closer to mach 0.5 in air. 358 meters/second is close... 662 mph is close.

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).

Indicated airspeed, as sibling comments point out, is not true airspeed. The air is moving at 500 but the stagnation pressure is the same as if it were moving only 300 at sea level so the indicated speed will be 300 +- calibration errors.

Re: A330 flight control laws saved Voyager, inquiry finds

#25

Post by NikolaeVarius »

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?

Controls laws on an Airplane is an extremely tricky subject and there is no real consensus as to how to deal with conflicting inputs.

Re: A330 flight control laws saved Voyager, inquiry finds

#26

Post by mikeash »

djrogers wrote: post #22
mikeash wrote: post #9

Earlier quoted context omitted.

Indicated airspeed is based on the force of the oncoming air, and decreases as air gets less dense. There's some altitude where 358kt indicated is Mach 0.9. Edit: before I get more replies attempting to lecture me on how wrong I am, please look up the difference between true airspeed (how fast the air is moving past the airplane) and indicated airspeed (a measurement derived from the difference between static and dyn…

That's not correct. At 33,00 ft, Mach 0.9 is about 600Kts, the altitude charts don't go high enough for Mach 0.9 to be 358Kts - by that point yo haven't enough air to transmit sound. And if you're implying that 358kts indicated could be 600kts actual with the right tailwind - that's true, but it still wouldn't be Mach 0.9, as the speed of sound applies only to airflow over the airplane. No matter the tailwind, the ai…

It has nothing to do with wind. 358kts indicated at 30,000ft translates to about 670kts true airspeed, for example. It's purely a result of how airplanes measure speed.

https://en.m.wikipedia.org/wiki/Indicated_airspeed

Re: A330 flight control laws saved Voyager, inquiry finds

#27

Post by awinter-py »

not sure it's legit for airbus to be declaring a win for their automation. sounds like the copilot dogpaddled back to the cockpit through freefall and batted at his controls from the ceiling until the computer got confused and resumed level flight.

If any safety technology deserves credit here it's seatbelts. From the sound of it, nobody who was belted in was injured.

Re: A330 flight control laws saved Voyager, inquiry finds

#28

Post by mikeash »

kristianp wrote: post #20
Someone wrote: post #7

"seven dented ceiling panels, 50 damaged in-flight entertainment sockets" The article doesn't state it, but that's because the passengers, like the co-pilot, fell towards the ceiling of the airplane during this episode. Apparently, the headphone cables are stronger than those sockets.

It's a safety concern that at least 50 passengers didn't have their seat-belts on!

And this is why they tell you to always keep your seat belt fastened when seated, even when the seat belt light is turned off. You never know when a sudden maneuver or severe turbulence might hit.

Re: A330 flight control laws saved Voyager, inquiry finds

#29

Post by cypherpunks01 »

Shouldn't there be an override switch to tell the plane to only accept one of the two control inputs, for situations like this where one of the inputs suffers some physical damage or jam? None of the hundreds of cockpit switches does that?

What happens if one pilot dumps their entire cup of coffee onto their controls and it malfunctions causing erroneous input? Is it basically game over?

Re: A330 flight control laws saved Voyager, inquiry finds

#30

Post by hlandau »

cypherpunks01 wrote: post #29

Shouldn't there be an override switch to tell the plane to only accept one of the two control inputs, for situations like this where one of the inputs suffers some physical damage or jam? None of the hundreds of cockpit switches does that? What happens if one pilot dumps their entire cup of coffee onto their controls and it malfunctions causing erroneous input? Is it basically game over?

There is. Google "sidestick priority".
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