Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Ryanair flight landed at Manchester airport with six minutes of fuel left

theguardian.com

Post reply on HN
Print view View original

451–460 of 586 posts

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#451

Post by Gibbon1 »

johndubchak wrote: post #325
alwa wrote: post #209

Earlier quoted context omitted.

(1) The turbofan category of jet engine seems to inspire a lot of very pretty animated technical diagrams—here’s one set from a German manufacturer [0]. Now if only we could convince Bartozs Ciechanowski to take on such a subject… [1] (2) I know glider pilots who fly without any fuel at all, once aloft… sounds not unlike the 150-200km glide range that @MaxikCZ mentions at idle from cruising altitude. [0] https://aero…

Regarding the turbofan and [0], above...if you're communicating to a non-engineer (me), how does the design get to the point of such complexity? I would love to learn the design story behind such an incredibly complex piece of machinery. I am being serious, if you cannot tell.

For the same thrust it's more efficient to accelerate a large mass of air a small amount than t accelerate a small mass of air a large amount. The fan is what gives you that.

I rough guessed the cost of fuel over a 737's life as $150 million. Where the engines cost something around $30 million. That pushes the engineering economics towards maximizing the engines efficiency.

I'm suspicious that bypass ratio's for turbofans are close to maxed out. The diameter of the fan gets unwieldy. That was the design issue that the 737 Max was trying to get around. With bad results. Possible the future is hybrid designs with two engines and 4 or more electrically driven fans.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#452

Post by LikeBeans »

alterom wrote: post #437
TZubiri wrote: post #414

Earlier quoted context omitted.

My guess is higher air density means more wind resistance, which acts as negative forward acceleration.

Not just that. Jet engines are efficient at higher speeds because the exhaust of the jet engine is fast . If the plane is going fast as well, that exhaust is more or less stationary relative to the ground. The engine works to exchange the position of the plane with the position of the air in front of it. If the plane is going slow, it's accelerating the air backwards . That's where the work is going, making the engin…

So perhaps the differential air speed between the intake and exhaust is a big factor in the efficiency equation? The bigger the difference the more work is needed..

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#453

Post by kqr »

abtinf wrote: post #40
jacquesm wrote: post #23

That is very exceptional. I've written fuel estimation software for airliners (cargo, fortunately), and the number of rules regarding go-arounds, alternates and holding time resulted in there usually being quite a bit of fuel in the tanks on landing, by design. I've never heard of '6 minutes left' in practice where it wasn't a massive issue and the investigation into how this could have happened will make for interes…

Naively as an outsider, this situation seems like everything worked as intended? On a nominally 2h45m flight, they spent an extra 2 hours in the air, presumably doing doing fuel intensive altitude changing maneuvers, and were eventually able to land safely with their reserves almost exhausted. I’m a little confused by what there is to investigate at all. How much fuel should they have landed with?

In safety-critical systems, we distinguish between accidents (actual loss, e.g. lives, equipment, etc.) and hazardous states. The equation is

hazardous state + environmental conditions = accident

Since we can only control the system, and not its environment, we focus on preventing hazardous states, rather than accidents. If we can keep the system out of all hazardous states, we also avoid accidents. (Trying to prevent accidents while not paying attention to hazardous states amounts to relying on the environment always being on our side, and is bound to fail eventually.)

One such hazardous state we have defined in aviation is "less than N minutes of fuel remaining when landing". If an aircraft lands with less than N minutes of fuel on board, it would only have taken bad environmental conditions to make it crash, rather than land. Thus we design commercial aviation so that planes always have N minutes of fuel remaining when landing. If they don't, that's a big deal: they've entered a hazardous state, and we never want to see that. (I don't remember if N is 30 or 45 or 60 but somewhere in that region.)

For another example, one of my children loves playing around cliffs and rocks. Initially he was very keen on promising me that he wouldn't fall down. I explained the difference between accidents and hazardous states to him in childrens' terms, and he realised slowly that he cannot control whether or not he has an accident, so it's a bad idea to promise me that he won't have an accident. What he can control is whether or not bad environmental conditions lead to an accident, and he does that by keeping out of hazardous states. In this case, the hazardous state would be standing less than a child-height within a ledge when there is nobody below ready to catch. He can promise me to avoid that, and that satisfies me a lot more than a promise to not fall.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#454

Post by testaccount28 »

minetest2048 wrote: post #441
alterom wrote: post #437

Earlier quoted context omitted.

Not just that. Jet engines are efficient at higher speeds because the exhaust of the jet engine is fast . If the plane is going fast as well, that exhaust is more or less stationary relative to the ground. The engine works to exchange the position of the plane with the position of the air in front of it. If the plane is going slow, it's accelerating the air backwards . That's where the work is going, making the engin…

That sounds like Oberth effect in rocketry, where the faster you go the more efficient your rocket be: https://en.wikipedia.org/wiki/Oberth_effect

they have nothing to do with each other.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#455

Post by jacquesm »

PunchyHamster wrote: post #385
abtinf wrote: post #40

Earlier quoted context omitted.

Naively as an outsider, this situation seems like everything worked as intended? On a nominally 2h45m flight, they spent an extra 2 hours in the air, presumably doing doing fuel intensive altitude changing maneuvers, and were eventually able to land safely with their reserves almost exhausted. I’m a little confused by what there is to investigate at all. How much fuel should they have landed with?

Might not be about fuel but about why they even tried instead of diverting earlier. Might even be 100% done by the book but book needs changing (tho I doubt that, it's not exactly first case of "a lot of bad weather")

Our definition of 'bad weather' is definitely changing as we gather more data.

Besides regular weather (which airliners aim to avoid except during take off and landing) there are many other factors at play here. There are several almanacs that are used for fuel calculations & navigation, they are updated annually.

The fastest jet stream (the aviation equivalent of the trade winds) recorded is north of 400 Kph, having that with you, against you or perpendicular to your flight path will have a substantial influence on fuel consumption and flight duration.

I agree with you that it may well end up with a regulatory change but that's one of many possible outcomes here. I will definitely keep an eye out for the report on this flight's investigation. It is going to make for very educational reading.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#456

Post by jacquesm »

jenadine wrote: post #432
paulddraper wrote: post #59

Earlier quoted context omitted.

At what point should they investigate? 0 minutes? -1 minutes?

They should investigate after the first failed landing, regardless of the amount of fuel in the tank.

Go arounds are perfectly normal and are not a 'failed landing', a failed landing is a crash.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#457

Post by Aeolun »

amadeusw wrote: post #438
ant6n wrote: post #300

Earlier quoted context omitted.

The greenhouse effects of flying is about 3-5x the effect of just burning the fuel.

What do you mean by this? What else than burning the fuel contributes to the greenhouse effect?

Building the airplanes? Servicing them? Heating the airports?

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#458

Post by traceroute66 »

aeronaut80 wrote: post #234
traceroute66 wrote: post #74

Earlier quoted context omitted.

> But it was a valuable lesson learned in speaking up before you get to that point. I'm not sure it was a lesson learned per-se because the captain was merely doing his job as fundamentally defined. A captain has ultimate responsibility for the aircraft . However there is a side question in relation to your post... When you say "declared an emergency" in your post, the more interesting question would be whether it wa…

The word Mayday is not required to declare an emergency. Pan pan still indicates an emergency. And neither phraseology is required as long as the intent is clear, see https://www.faa.gov/air_traffic/publications/atpubs/atc_html... In fact, it doesn’t even need to be the pilots who declare an emergency https://hsi.arc.nasa.gov/flightcognition/Publications/non_EA...

> The word Mayday is not required to declare an emergency.

That may be so in the US.

But it is a bad habit to pick up.

Especially if you are an airline pilot and you frequently fly to destinations where English is not the first language.

Or indeed in US airspace where you frequently get international carriers flying in and out.

There is a reason why there is internationally agreed standard phraseology for radio communications.

Everyone learns MAYDAY/PAN and the associated expectations around it (e.g. radio silence etc. etc.)

Not everybody will be able to adequately follow along if you have a long drawn-out waffle discussion over the radio ... "we have a little problem" ... "do you want to declare?" ... "oh wait, standby ...." ...."oh, we're ok for now" ... "oh actually maybe this or that"... yada yada yada.

If its truly an emergency then cut the crap and use the standard phraseology and keep the communications terse.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#459

Post by whycome »

School-Cotton wrote: post #356
whycome wrote: post #210

Earlier quoted context omitted.

[flagged]

Why do people keep insisting on pasting LLM output to HN when every time it happens, it gets downvoted to oblivion? The community clearly doesn't want it. If we wanted to know a computer program's opinion about something, we could ask it ourselves.

I was using it to question that exact stated fuel consumption number without a citation. For hard data (like fuel consumption) getting a value from an LLM isn’t absurd.

Re: Ryanair flight landed at Manchester airport with six minutes of fuel left

#460

Post by whycome »

lawlessone wrote: post #307
whycome wrote: post #210

Earlier quoted context omitted.

[flagged]

ok, how do we verify that?

That’s the point? I wasn’t suggesting it was correct. Just that the value is wildly different from their own non-cited number. The next stage was to get a citation from an actual datasheet. Their reasoning was nothing beyond “I’ve read”
Post reply on HN