It's _exactly_ the kind of comment that deserves to be downvoted here.
It's curiosity, it's learning, it's looking for an explanation.
That's exactly the kind of comment that deserves to be here.
>[...] who doesn't have any relevant expertise,
Is that a requirement to comment on this thread?
Do you fulfill that requirement you brought in?
If I'm wrong, then apologies to the OP.
Yes, I've been on this website quite a long time, unfortunately.
Is that the topic of this thread?
So I was wondering what if current plane designs had 4 smaller but equally as efficient engines instead of 2. The vast majority of airplane accidents happen at takeoff or landings, if some of those can be avoided by having 4 engines for commercial aircraft, its a worthwhile idea to explore.
Also I would venture that 99% of comments on public forums like this are from people without expertise. My expertise in this space is a curiosity about planes for a few decades, taking some actual flying lessons, and being generally interested in aviation to go to airshows, watch youtube content from pilots, etc. I probably have about the same aviation knowledge as an average HN person.
Larger jet engines are more fuel efficient than smaller ones, because larger diameters allow for more bypass air and therefore more fuel efficiency [1]. It is a function of size and a lot of the engineering goes into materials and designs to be able to increase size and maintain strength. So you simply can't make 4 engines that are as efficient as 2 large ones, and that is compounded by the significant additional weight (and drag) of the duplicated engine parts and mounting structures.
>if some of those can be avoided by having 4 engines for commercial aircraft, its a worthwhile idea to explore
Everything comes with tradeoffs. Adding more engines mean more complexity, more maintenance, more chance of single engine failures, etc. You don't want to introduce more failure modes than what you are trying to fix. The move to two engines for large aircraft and the evolution of ETOPS (Extended Twin-engine Operational Performance Standards) involved a lot of people considering a lot of scenarios. I can guarantee the "why not 4 engines" question has been studied extensively.
[1] https://simpleflying.com/why-do-jet-engines-keep-getting-lar...
Impossible to answer until we know the cause. If it was independent powerplant failures, then yes. If it was e.g. fuel contamination, pilots improperly shutting down the engine, some other crap failing, then no.
Speaking as someone with aerospace engineering and GA pilot experience.
"4 smaller but equally efficient engines" feels like a unicorn though (we'll probably get to the point in future where four large engines are superior in efficiency to two of today's engines, but two large engines to that latest design will still be more efficient than four smaller ones...)
With turbines, yes, for fundamental reasons. With electric motors, on the other hand, perhaps not, though not particularly relevant to a long-haul route like AMD-LON.
(I get to write about arrayed space thrusters in the day job too, but again, fundamentally different physics and goals...)
It's pretty clear what the guy is inquiring about.
Speaking as someone without aerospace engineering or GA pilot experience. My only relevant experience here is being able to read.
Double bird strikes are “independent powerplant failures.”
Apologies!
Smaller turbofan engines are less efficient than larger ones. This is because they have a lower bypass ratio - thrust generated by turning the big fan over the thrust generated by combustion.
So expect even bigger engines.
Unironically, you're probably way more qualified than most of the people here throwing rubbish at you.
A classic on places like this.
We won't know until we have all the details and the exact cause of the shutdown.
The passengers could just take turns going out and pushing.
But it is somehow implied that the context of the comment is normal driving conditions.
Perhaps that comment could be reworded like:
>When driving on a highway, while not being pursued by the police, on planet Earth, with a road temperature below 200C, and not driving behind a van transporting nails with an open door that's dropping them on the road, why don’t all four tires on a car blow out at the same time?
That way people could get a better sense of what it is about.
Any time after it’s too late to abort takeoff.
Pilots should be able to “regain full control of the aeroplane without attaining a dangerous flight condition in the event of a sudden and complete failure of the critical engine…at each take-off flap setting at the lowest speed recommended for initial steady climb with all engines operating after takeoff…” [1].
[1] https://www.easa.europa.eu/en/downloads/136694/en 25.143(b)(1)
Aircraft can land (in right circumstances) by gliding in sans power .. the same cannot be said for take offs.
Aborting above V1 is heavily discouraged because usually there's a strong risk of running off the end of the runway. Of course, if you lose both engines above V1, you're really in trouble and left without much choice.
But we don't know what happened with this flight so nothing I've said here should be taken as indicative of whatever went wrong in this case. It's purely information.
[0] Which depends on many factors including the type of aircraft, loading, weather conditions, state of the runway surface - for example, wet, or iced - etc., and needs to be calculated afresh for every take off.
An airliner in the US did it and the pilot was praised for making that hard decision. Everyone walked I think. I forget which flight.
One a plane reaches v1 during takeoff, it can lose an engine and still takeoff.
It an engine was lost before v1, the takeoff would be aborted.
Here is an Airbus doing just that.
There are many factors at play and things are complicated by unexpected failures.
Thank you for the video that demonstrates a pilot aware in advance of planned "engine failure" can cope with such an event in scheduled test conditions.
The phrase "line kilometres" might indicate a smidgeon of aviation industry adjacency to some.
EDIT: Above and below comments appear to be low grade random sniping in bad faith.
There's a failure to address content and specifics and a straw assertion about "more insight than the pilots, engineers and safety regulators", a claim that was never made.
At best I have the same insights as anyone that worked with 20 airframes for a few decades and staged them about the globe in that time.
EDIT2: Symbiote has deleted their problematic reply below that the first edit was made in response to. The michaelt reply came after the reply by Symbiote and is moot, all my statements are here, undeleted and unredacted.
Everyone in the formula 1 subreddit uses jargon, none of them are F1 drivers.
The statement I made:
> Aircraft can land (in right circumstances) by gliding in sans power .. the same cannot be said for take offs.
is about having _no_ thrust power during take off.
The other statement I made acknowledged that test pilots in planned and scheduled clear weather conditions often test aircraft with mock engine failures, then pointed out that this is very different to an unexpected failure during non test flights.
Yes, sometimes these things work out alright (as per your example), other times not so much.
Landing sans power is landing with no thrust (no functioning engine).
Completing a take off with no thrust isn't possible unless the craft is a glider, a hot balloon, or a ballistic launch .. taking off with a single engine is not "taking off sans power".
Constructing solutions for multiple-mode failures like this is a bad engineering smell. Almost always the solution isn't actually helping anything, and often makes things worse in whatever metric you're looking at. In the example here, having four engines makes the chances of total thrust loss lower, but it doubles the chance of a single engine failure. And the literature is filled with incidents of theoretically-survivable single engine failures that led to hull loss as a proximate cause (generally by confusing or panicking the crew).
The most well known double-bird-strike incident is probably the one where Sully landed a plane on the Hudson River.
https://en.wikipedia.org/wiki/US_Airways_Flight_1549#Takeoff...
-edit: ok, everyone had the same thought, haha -
There was this very famous double bird strike https://en.m.wikipedia.org/wiki/US_Airways_Flight_1549
There certainly have been bird strikes that disabled all engines.
What? It happens multiple times a year. They made a movie about a famous incident (US Airways Flight 1549). There's even events with four engine strike (Eastern Air Lines Flight 375).
So far this year, it's happened at least twice resulting in engine failure.
Jan - Air New Zealand NZ207 - aborted take off following dual bird strikes and both engines damaged.
~~Mar - Ryanair FR 4102 - dual bird strikes on landing resulting in injuries and hull loss.~~
Before that, in December 2024, Jeju Air Flight 2216 crashed on landing following dual bird strikes, resulting in the loss of all PAX.
These aren't as rare as you believe they are.
Selection bias
The lower the barrier to entry of the subject matter the lower quality the people discussing it. This crap is like the Kardashians for white nerds with stem degrees.
The people with the requisite dozen brain cells to common sense realize these problems are complex and keep their mouths shut.
But in the video of the plane taking off and crashing, there's no clear, obvious, or tell-tale "poof" of bird turning into exhaust as there often is in bird strikes.
That doesn't rule it out.
(In that case they were at cruising altitude, so had time to handle the situation and relight the engines).
https://www.youtube.com/watch?v=z_ewa7R20MA
Lufthansa 747-8 after engine failure:
*We're not an emergency.*
Most airlines avoid nowadays the invest into maintenance of four engines airliners. Others have prefer the additional transport capacity and margins. Lufthansa has it's own maintenance branch "Lufthansa Technik" and doesn't need to handle extra costs. Emirates needs the huge capacities of the A380.
PS: The 747 can and does - if necessary - ferry flights without passengers and only three engines. Not possible with twin engine planes.
I think it's more that they needed the prestige of having the biggest planes, offering a whole bedroom with shower etc. It goes well with their ultra luxury image.
If it's just about seats that can fly smaller ones with the benefit that they can operate more frequently and thus attract more transit passengers looking for a good connection. That's their main market.
An A380 is quite a hassle because most airports can't even handle one.
Connect major hubs like FRA with JFK and it makes sense. You need capacity, it is a long route and slots are rare and expensive. And for Emirates the hub concept is crucial.
But yes. The luxury thing is also part of their show. But it fills the plane ;)
Many operators dropped the 380 during COVID. Makes sense but they never took them back on afterwards and passenger numbers are higher than ever before now. The A380 is cool but it was built for the past not the future.
One has to wonder if this was a bird strike incident on both engines that maybe having 4 engines would have allowed the plane to circle back around.