@gsuberland right so the next question is "why is this an intellectually honest way to calculate per-passenger emissions"

@whitequark it does rather gloss over externalities doesn't it

@whitequark although even then the calculation has major uncertainty factors for reasons you don't even control as a passenger, like "did the flight sell out?" (since you're then dividing the constant mass of the aircraft by fewer passenger)

@gsuberland it's not even constant! the amount of fuel would vary with the amount of passengers (as well as the route and decisions like "do we need to take on fuel for the flight back / next flight")

@gsuberland @whitequark the aircraft and fuel weigh much more than the passengers and their luggages (like 10x by my napkin) so I think it's not an unreasonable simplification to just divide the trip emissions into the passengers by the space they take.

@chrisvest @gsuberland for a B737-600, the empty jet weighs 36t and the passengers would weigh ~13t if i go with the "dense but still realistic" seating. so it's not an order of magnitude

edit: fixed typo (767->737)

@whitequark @chrisvest and even just from passive consumption of ACARS Drama it seems clear that aircraft are fuelled to significantly different levels depending on the passenger load.

(although I did also know this from other sources)

@whitequark @gsuberland I looked at the 787 on wikipedia and its in a 200t-250t weight class, with the 787-10 carrying up to 310 passengers. I picked 85kg per passenger+luggage ( maybe that’s low) which gave me 26.3t

@whitequark @gsuberland I think your numbers are off, though I can’t find the 767-600 specifically. A 767-300 has max take-off weight of 158t and max payload of 40t. I can’t imagine the fuel makes up the difference.

@chrisvest @gsuberland source

@chrisvest @gsuberland oh, sorry, i made a typo. it's 737, not 767

@whitequark @gsuberland ooh, yes, tracks. Seems like, the smaller the plane, the bigger a percentage of the take-off weight the passengers can take.

@chrisvest @gsuberland that is an even stronger argument against making a single pair of figures for economy/business: it strongly depends on the composition of the fleet!

@gsuberland @chrisvest meatbags: fuckin heavy, actually

@gsuberland @chrisvest i was curious and did some calculations, apparently if you go with some reasonable assumptions (158 cm max linear dimension for checked bags, 30 kg max weight) then the checked bag density must be no more than 1/5 of passenger density

@whitequark @chrisvest related: a lot of lift weight capacities are actually pretty terrifying when you do the numbers. very easy to overload a lot of them with just a few tall heavily built people. and the safety margins on a lot of them are... uh... degraded.

@gsuberland @chrisvest huh. well, that's one more thing i'll proceed to not think about

@whitequark @chrisvest the good news is that there are like 4 redundant safety mechanisms to prevent plummets, and a couple of them are effective far beyond the stated weight capacity, even with worst-case dynamic loads. but the experience of stepping into an aging lift that barely had the capacity for two people when first installed, and feeling it drop a full 6 inches, is deeply alarming.

@whitequark yeah true. it's the fuel to carry the fuel problem

@whitequark @gsuberland a question i am asking from a place of total ignorance and curiosity: do commercial airlines vary the amount of fuel they take based on the total weight of the boarded flight and expected distance?

they keep finding ways to pack flights fuller and fuller (at least in the merica), which goes against how i would expect cost optimization to work unless they were being really wasteful with fuel to begin with

@aeva @gsuberland

a question i am asking from a place of total ignorance and curiosity: do commercial airlines vary the amount of fuel they take based on the total weight of the boarded flight and expected distance?

yes, this is a really important factor in the pre-flight calculations and getting it even a few % off can have serious consequences

@aeva @whitequark all of that, plus weather.

@aeva @gsuberland

they keep finding ways to pack flights fuller and fuller (at least in the merica), which goes against how i would expect cost optimization to work unless they were being really wasteful with fuel to begin with

don't forget that airlines often lease most of their planes rather than outright owning them (and even if they own it they took out a loan first), so any idle seats or idle planes cost them a lot of money regardless of fuel

@whitequark @aeva @gsuberland what i'm more curious about is if they use counts of pax/bags or if they use some kind of sensors in the landing gear to get actual weight.

When you're flying little single engine stuff it's common to actually weigh everyone and bags to make sure you're not too unbalanced

@azonenberg @whitequark @aeva airlines and safety bodies rely on "Standard Passenger Weight" studies for the passenger part. baggage is weighed.

the figures include uncertainties.

@azonenberg @whitequark @aeva @gsuberland I have had a flight tell passengers (after boarding) that they were going to offload some luggage for weight reasons so they do have sensors as well, apparently.

@wronglang @azonenberg @whitequark @aeva it's measured at check-in. they were probably offloading because they sold based on median luggage weight and your flight happened to be an outlier on what people actually arrived with.

@wronglang @azonenberg @whitequark @aeva like the baggage allowance is 23kg or whatever but they assume the average bag on any given flight is lighter than that 'cos designing the limits around the upper bound is inefficient. if everyone shows up with 21-23kg bags then it's too much, but that's really rare.

@gsuberland @azonenberg @whitequark @aeva huh, I would've assumed they'd do that before boarding but 🤷

@wronglang @azonenberg @whitequark @aeva they don't usually finish loading bags until they're already boarding. plus until everyone's boarded you don't know how many people no-showed.

@gsuberland @azonenberg @whitequark @aeva yeah that makes sense, funny to have just inferred that wrong

@azonenberg @whitequark @aeva obviously it's not globally static - average passenger mass in Texas is gonna be very different to Singapore.

@gsuberland @whitequark @aeva checked, i assume you mean? i've never had anyone weigh my carryon

@azonenberg @whitequark @aeva yeah checked. since carry on is restricted you can assume a fixed upper bound per passenger.

@gsuberland @azonenberg @aeva oh right they probably do it when you check it in

@whitequark @azonenberg @aeva yeah check in bag weight is how they measure that part