14 ms·

That is very exceptional. I've written fuel estimation software for airliners (cargo, fortunately), and the number of rules regarding go-arounds, alternates and

• psunavy03 1y ago
  And the reason why those fuel reserves exist is to be a guard band allowing situations like this to happen without flames, wreckage, and death. Having worked with many US airline pilots over the years, this is also why they are so proud to be unionized. Sure, senior pilots make as much as some FAANG developers, but the union is also there so that management doesn't get bright ideas about things like cutting fuel reserves to cut costs without the union telling them to stuff it.
  • jacquesm 1y ago
    Management can't cut fuel reserves, not because the pilots are unionized but because there are some very strict rules about these fuel estimations prior to take off and margins be damned. And those rules are exactly there because otherwise this kind of incident would happen far more frequently. But it's regulation that is the backstop here, not the pilots.
    • psunavy03 1y ago
      The point is that the unions are there to allow the pilots to advocate for all kinds of safety-of-flight related things like fuel reserves, crew rest, and so forth that management would be happy to cut to save money. And to do so without fear of retaliation. And if you don't think the airlines would love to lobby Congress about the regulatory backstop, well . . .
      • jacquesm 1y ago
        As I wrote elsewhere in this thread I actually wrote software to estimate the amount of fuel a jet should load to comply with the rules. This was commissioned by the airline and they were scared shitless that they would ever be found to be in breach of the regulations on this aspect. It is one of those red lines that you really do not wish to cross. There are other aspects of flight where you are right but this particular one is different. The main reason why airlines would like to take the least amount of fuel is because it immediately increases payload capacity and thus flight efficiency. This being a cut-throat market there is a serious incentive to cut it as fine as possible. So the regulations around this particular issue are incredibly strict: you have to have a certain amount of fuel left upon landing, you have to write up truthfully how much you still had left and you will be investigated without fail if you cut into the reserve. The good thing about unions here is that they help to make sure that pilots know they are safe reporting truthfully because the airlines can not retaliate if they would pressure the pilot to not report an incident (which all pilots would normally definitely do). So they're a factor, but it is the regulator that writes the rules here and they are super strict about this. And that's immediately why the calculation of the estimate becomes so important: you now have 30 minutes (or 45, depending) of deadweight + the deadweight for two alternates and an x amount of time in a holding pattern, plus up to three go-arounds. That really adds up, so you have to do your best to get the calculation as close as possible to what it will be in practice without ever cutting into that reserve. It took me the better part of a year and massive amount of learning to write a small amount of code + associated tests to pass certification. It also taught me more about software engineering (as opposed to development) than anything I did up to that point in time and it made me very wary about our normal software development practices.
        • in_cahoots 1y ago
          As an aviation fan just reading this thread is quite eye-opening in terms of how much risk tolerance the average commenter has vs what is standard in the aviation community and on aviation forums. It's almost like peeking into two different worlds. I wonder if there would be any value in teaching an "engineering when lives are on the line" or "war stories from accident investigations" classes to new engineers. I feel like there's value in appreciating just how much more work goes into building a system where people's lives are at stake.
    • jMyles 1y ago
      ...that regulation is text in a database. It can be changed capriciously at any moment, like they often are. It takes people with ideas and a willingness to put pressure in the right places to be sure that sane policies prevail. I think it's pretty obvious that as time moves forward, we need to rely on "regulations" less. The root and history of the word in the political context is to make things regular. But state actions increasingly bring irregularity to the world. It seems absolutely fair to say that, in this situation, the people - the pilots in particular, but also cabin crews, ATCs, engineers, and their unions, are the backstop worth observing and celebrating.
      • jacquesm 1y ago
        If you land with less fuel than the legal minimum you are going to have a lot of explaining to do, there will be an investigation and you, the pilot and the airline will get enough headache from it that you will make bloody sure it does not happen again. The pilot(s) may not be able to fly until that investigation has run its course, the airline may get fined or warned if this is the first time it happened. In an extreme case the pilots may lose their license. > It seems absolutely fair to say that, in this situation, the people - the pilots in particular, but also cabin crews, ATCs, engineers, and their unions, are the backstop worth observing and celebrating. I will hold off on that conclusion until the report is in. There are so many possible root causes here that speculation is completely useless, and celebrations would be premature.
        • jMyles 1y ago
          My apologies - I didn't mean to speculate about this incident in particular, but about the general role of so-called "regulation"; I thought it was unfair to minimize the role of the people and unions compared to the (in my view, comparatively flimsy) legislation.
      • rcxdude 1y ago
        I think the thing that's being pointed out as overlooked when praising the employees and the unions, is the regulators, who are the people who play a very large part in making sure that the regulations are enforced. The regulations are just text in a database, but it's the regulators who actually make it happen. A pilot who wants to push back against a beancounter cutting corners has a union and a regulatory agency to back them up.
    • yodelshady 1y ago
      Regulations are paper. Who enforces the behaviour, of whether to take off or not, on a windy night in central Italy? Of course the pilots are the backstop, and the unions are theirs, so they can make necessary calls the money doesn't like.
      • throwup238 1y ago
        The union is a nice backstop for issues around the edges that come up with corporate, but the real backstop is the pilots’ licensing. By making them directly responsible for the plane as PIC, it gives them leverage over their employer that few other professions have. AIR-21 gives them significant protection from retaliation and the ASRS is confidential. ALPA helps them navigate that mess if it comes to it, but that’s the real legal backing that pilots have. Same thing happens with Professional Engineers regardless of whether they are employed or work as independent consultants/firms. They’re legally responsible for the bridges and other infrastructure they sign off on with laws protecting them from employers and clients. (I fully support the ALPA and other unions, I just don’t think it plays as significant a role in following regulations as you claim)
  • parineum 1y ago
    > Sure, senior pilots make as much as some FAANG developers That's a funny way to phrase it. I'd probably go the other way and say "sure, FAANG developers make as much as some pilots..." Those pilots have hundreds of lives on the line every day.
    • kroolik 1y ago
      Those FAANG devs have milions of (social) lives on the line, though. Every day.
      • kpmcc 1y ago
        Is this a joke?
    • jacquesm 1y ago
      Yes. I think the average bus and train driver is completely underappreciated as well and they have a massive responsibility too. I know I could not do their jobs, it would weigh on me too much.
• abtinf 1y ago
  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?
  • _9ptr 1y ago
    30min+
    • jacquesm 1y ago
      Yes, I believe this is correct for this model aircraft.
  • fabian2k 1y ago
    My understanding is that they shouldn't have spent that much time in the air (not intended as a guess for the cause). The margin is there for situations where you can't land earlier, not the margin for scheduling the landing. There is margin for expected potential delays, they were in the other margin that should never be used except in true emergencies.
    • abtinf 1y ago
      Oh I think I see; so is the question not “why did they land with so little fuel”, but more like “why did it take so long to decide to redirect to a known-safe airport”?
      • fabian2k 1y ago
        I don't know. As the parent said, I'd be careful with guessing the root cause right now. They should not have been this low even if diverted due to weather.
      • jacquesm 1y ago
• jakub_g 1y ago
  How many go-arounds and alternates are usually accounted for? Assuming EU, high-airport density etc, typical 2h flight. Does the estimation change depending on weather forecast, season of the year etc?
  • jacquesm 1y ago
    3 go arounds + 2 hours in a holding pattern should result in at least 45 to 60 minutes left in the tanks after landing. Depending on the kind of aircraft that can be a pretty impressive amount of fuel. > Does the estimation change depending on weather forecast, season of the year etc? Yes. There are many factors that go into this including trade winds (which vary quite a bit seasonally and which can make a huge difference), time of day, altitude of the various legs, route flown, weather, distance to alternates, altitude of the place of departure and altitude of the place where you are landing, weight of the aircraft, engine type, engine hours since last overhaul, weight of passengers, luggage and cargo, angle-of-attack and so on. The software I wrote was a couple of thousand lines just to output a single number and 10x as much code for tests, and it was just one module in a much larger pre-flight application.
    • jakub_g 1y ago
      I can only imagine how the test suite looks like. Wild. This made me think about the fuel itself: is aviation fuel globally standardised and the same quality in every single airport in the world?
      • jacquesm 1y ago
        The test suite was much larger than the code. It took ages to get it certified, the calculations had to be correct to the last significant digit on reference problems to prove that the algorithms had been implemented correctly. This caused a bit of a headache because the floating point library that I used turned out to be slightly different than the one from the benchmark. There are three different kinds of jet fuel and all are produced to strict standards, and then there are allowances for ppm water contamination (very low, to ensure the fuel system will never freeze at altitude or in freezing weather on the ground or at lower altitude).
• YeahThisIsMe 1y ago
  I remember this stuff being a bigger story for a short moment x years ago, where low cost carriers (it might have been Ryanair then, too) routinely flew with unreasonably small amounts of "backup" fuel and had to declare emergencies in order to get on the ground safely. I guess they're trying it again now that the whole thing had blown over.
  • cosmicgadget 1y ago
    Pretty obviously not the case here if you read the article.
• coolThingsFirst 1y ago
  const estimateFuel = (distanceInKms, litersPerKm) => distanceInKms * litersPerKm;
  • deleted 1y ago
    [deleted]
  • BenjiWiebe 1y ago
    I don't even know what I'm talking about, but you at least forgot to account for headwinds and differing drag amounts at different altitudes/speeds.
    • jacquesm 1y ago
      The big one is the trade winds. Those can really kill your efficiency on long distance flights.
    • coolThingsFirst 1y ago
      Yes it was a bit of humor, sad it didn’t land.
• fidotron 1y ago
  I have known former air traffic controllers that won't fly certain airlines because of a notorious habit some have for queue jumping by claiming they're low on fuel. If they are low on fuel is something else, but in any case when the ATCs have noticed a pattern then something is up. This situation sounds a lot less nefarious, but it does also sound like they should have rerouted earlier.
  • kpmcc 1y ago
    Which airlines? I feel like if this is an issue we should be naming names.
    • estebank 1y ago
      RyanAir is famously one of them. Edit: I was recalling articles claiming the company purposely fueling less than other airlines in order to increase their rate of claims for priority landing to have a better "on time" statistics. This forum post disputes that: https://aviation.stackexchange.com/questions/38501/is-it-true-that-ryanair-flies-without-fuel-reserves https://aviation.stackexchange.com/questions/38501/is-it-tru...
      • PunchyHamster 1y ago
        also carrying less fuel does save on fuel usage
    • fidotron 1y ago
      No way. Having attended meetings at ICAO I can also tell you many details of various aviation incidents, including their existence, are covered by some secret classification. This fact being disclosed caused most of the attendees to lose all hope in the rest of the proceedings. To their credit the FAA reps on that occasion were by far the most reasonable gov representatives in the room, and the FAA are one of the major voices pushing for greater transparency on it.
      • nradov 1y ago
• geor9e 1y ago
  Do forecasted storms go into the fuel estimate formulas?
  • deleted 1y ago
    [deleted]
  • jacquesm 1y ago
    Yes. Even not forecasted storms in the form of a probability of wind at low altitude when the engines are at their least efficient. And tradewinds at altitude, which are quite variable as well.
• deleted 1y ago
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• huijzer 1y ago
  > I'd be very wary to get ahead of the investigation and make speculative statements on how this could have happened, the one thing that I know for sure is that it shouldn't have happened, no matter what. Just watch Juan Browne, he usually turns out pretty good in analyzing the mishaps. He didn’t upload anything for Manchester yet but will probably soon: https://youtube.com/@blancolirio https://youtube.com/@blancolirio
  • loeg 1y ago
    I'm also a Blancolirio subscriber. Juan also doesn't try to get ahead of the investigation, really. It's part of what makes him a valuable voice in the space.
    • jacquesm 1y ago
      Anybody that does isn't worth listening to.
• bartread 1y ago
  Yeah, again, I’m going to wait for the Mentour Pilot analysis on this one.
• j45 1y ago
  Very insightful, thanks. Glad everything was ok. All I had to contribute was to ask if they were trying to hypermile or something?
• davesque 1y ago
  Yeah, to give some idea, I believe the technical term that would have been radioed from the pilot in this situation would have been "mayday fuel."
• ecommerceguy 1y ago
  I'm just curious, is this hard on the fuel pumps? I've always been told to not run gas down in your car because the pumps will get hot.
  • t0mas88 1y ago
    The pumps are fuel cooled, but it's designed such that the pumps remain in the fuel even in a low fuel situation.
• ChrisMarshallNY 1y ago
  > it shouldn't have happened, no matter what You hear that a lot, with Ryanair stories. Sounds like a great airline!
  • patrickmcnamara 1y ago
    Ryanair has an impeccable safety record.
    • deleted 1y ago
      [deleted]
• XorNot 1y ago
  This honestly makes me think that we're missing a trick if an option for this sort of circumstance can't be "send a military fuel tanker up to refuel them in air" as a last ditch emergency measure (which IMO you would've triggered in this exact scenario). The argument in favor is simply that we need in air refueling for the military, but justifying all that expenditure is a lot easier if it's dual use technology.
  • darthwalsh 1y ago
    Isn't midair refueling notoriously difficult to get right? The headlines would become "airliner crashes after crew couldn't thread the needle for 45 min"
    • jacquesm 1y ago
      It's a ridiculous proposition.
• TZubiri 1y ago
  >I'd be very wary to get ahead of the investigation and make speculative statements on how this could have happened >Ryanair I wouldn't be so wary.
• bboygravity 1y ago
  "make speculative statements" isn't this 99 percent of modern infotainment "journalism" though? making speculative statements, omitting and lying..
• PaulRobinson 1y ago
  The context you're missing is that Ryanair have routinely declared fuel emergencies in the past, and it seems an operational tactic - they want to carry less fuel to burn less fuel, and then have to regularly mayday to jump the stack on inbound, saving cash. That's not covered in the article, but you can sure as hell expect the CAA are going to take another look at them and their operations planning. On this one, they did 3 attempted landings at Prestwick. [Edit: I now see that the third attempt was at EDI] What happened between the first and the second landing that made them think on their second go-around that a third attempt was more likely to succeed than the previous two? Was the wind dying down, or was the captain just feeling a bit braver or stupider? [Edit: I'm still curious as to what information they gathered that landing conditions were significantly different at EDI to make that diversion, given its relatively close and so likely to have similar weather]. Why was their final reserve Manchester when there were literally dozens of closer suitable airports, at least some of which are likely to have had better wind conditions by virtue of lower gusts, or more aligned to runway direction so not dealing with a strong crosswind? There are many reasons I won't fly Ryanair, but not least because they have been shown over and over again to make reckless planning and operational decisions, and they are fortunate to have not had hull losses as a result. Time is ticking down, variance will catch them one day, and a sad & tragic catastrophe is only a matter of time. People will go to prison as a result, because this pattern of behaviour shows that this isn't "bad luck", it's calculated risk taking with passenger and crew lives to save money.
  • normie3000 1y ago
    > There are many reasons I won't fly Ryanair I swore off them a decade ago when I realised how adversarial their relationship with their passengers is. Until an accident does happen, I have no doubt they'll trouser a lot of cash.
    • gizajob 1y ago
      I fly with them all the time and never have any kind of issue at all. They offer a good deal, ok there’s a couple of obvious dark patterns in their app and way of doing business but they’re hardly unique in that respect. Feels like getting a fast bus between European cities nowadays.