🧠 Musings

Does Flying Spirit Help Save the Environment?

2022-01-16

In my previous blog, I described my experience flying Spirit Airlines for the first time. Spoiler: it wasn’t that bad, and I honestly will likely do it again.

I ended that on a note about how I suspect Spirit may actually be emitting less harmful stuff by way of flying lean and reducing its mass load. Below I detail some napkin math that I did on board the plane (well not literally, because they didn’t even give us napkins) and while writing the previous blog. If my estimates are in the right direction, flying Spirit might make even more sense because they contribute less CO2 emissions than other airlines when flying the same route!

Estimating Environmental Effects with Non-Legit Math

When Spirit flies leaner, the aircraft has less weight to counter. I think that means a shorter takeoff distance, higher potential rate of climb, and lower engine thrust requirements.

Spirit’s tiny tray tables were the first apparent weight reduction I noticed, so I’m going to use them as the focal point of my napkin math. They’re also easy to visualize.

I suspect airplane tray tables are made with some injection molded plastic. I believe some of Spirit’s older interiors have tiny aluminium tray tables, while their newer design incorporates plastic. However, I’m not super familiar with the vast family of plastics so let’s assume they’re made of consumer grade PLA, which has a density of 1.24 g/cc.

I estimate the dimensions of a non-Spirit airlines tray table match the dimesions of a 13-inch MacBook Pro, at (1.49 * 30.41 * 21.24) cm. This means the maximum mass of a PLA tray table is about 1193.38 g, assuming it’s literally just a slab of plastic. Let’s say designers are able to reduce its mass by 30% through smart structural design. That results in a mass of 835.37 g.

I should’ve measured the Spirit tray table, but my guess is the top surface area of the table was about 40% of what I’ve seen with other carriers. Following the same calculation as above, I’d guess the mass of a Spirit tray table is 334.15 g.

There are 39 rows in Spirit’s A321-200 plane, resulting in a total seat count of 234. I will assume all these seats have the same Spirit tray table, though that’ll clearly be incorrect for upgraded seats and emergency exit rows. Other airlines’ A321 configurations have a similar seat count ± a row or two, substituted with more business and first class seating. The total mass of a non-Spirit airline’s tables is 195,476.58 g. Spirit’s corresponding total is 78,191.10 g. Thus, the total reduction in mass via tiny tray tables in Spirit is 117,285.48 g. That’s about a 90th percentile adult man in the States!

Using ICAO’s carbon emissions calculator, the per-passenger CO2 emission for a flight from Detroit to Los Angeles is about 243.7 kg. I believe the calculator attributes about 150 kg of mass to every passenger+seat combo. Thus we can approximate that 150 kg of mass in the cabin corresponds to 243.7 kg of CO2 emissions for this flight. Using proportionality, I’d say the reduction in tray table mass results in about 190 kg less of CO2 emission in such a trip!

If you start counting the frequency of such trips daily, you’re probably going to go crazy. I say this because I had a mini existential crisis. If there are two DTW-LAX round trips daily (so the above journey happens four times daily) through an entire year, that’s 277,400 kg of CO2 emissions not released into the environment by simply reducing the size of tray tables. The EPA’s Greenhouse Gas Equivalencies Calculator says you need 340 acres of US forest to sequester that much emitted carbon in one year.

Spirit Airlines does not ship cargo, so I think these mass reductions will actually result in savings. And that’s just the effect of tiny tray tables! Imagine the savings from carrying less food and drinks; thinner seats; no recliner mechanism; and as a result, potentially less fuel. Spirit also somewhat discourages additional baggage by charging creative rates for it, though I don’t know if there’s a statistically significant decrease in passenger baggage on Spirit.

I know this calculation is backed by a ton of assumptions from the beginning to the end, but I think the general point is this: a budget airline cutting its mass load scales up to an improvement in fuel efficiency and a lower impact on the environment. I know these numbers still pale in comparison to heavily polluting industries, but I think personal responsibility is still important in protecting the environment.

I think I’m even more convinced that flying Spirit, where flying is necessary, is the way to go. And no, I wasn’t held at gunpoint or paid to write this.

~ Amal

Addendums

2022-01-21: Airports usually charge airlines for “slots” at terminal gates and routes. A number of airlines across Europe have been forced to fly empty flights to keep these slots. I remember seeing elsewhere that these slots are really hard to keep up with, and some airport authorities even fine carriers if they exceed their allocated time in a slot! Regardless, flying a transatlantic route on an etops-certified plane seems crazy unless the plane was carrying significant amounts of cargo or had an occupied corresponding return trip.

2022-01-27: Last week, a friend rightly pointed out that flying a Spirit v/s non-Spirit plane probably won’t cause a significant difference because a person’s mass will probably have the same effect on emissions in both planes. I think this makes sense, so I guess my argument sort of shifts to “more planes should be structured like Spirit’s in lieu of reducing emissions”.