Fleet Age Has a Price. Here’s the Data.

Yesterday, we introduced our Fuel Efficiency Index in a table looking at US airline single-aisle fleets. It provoked some conversation, so we're going deeper in this post. We're looking at the big airlines by fleet. The Next-Gen Premium: The MAX 8 and MAX 9 show up as hyper-efficient, sitting comfortably up in the 1.14 to 1.29 range. The A321neo Reality: Interestingly, American’s and Delta's A321neo sit right near the industry baseline (~0.98–1.04), while United's climbs to 1.20+. This perfectly highlights how network routing, stage lengths, or configuration densities change the field efficiency of the exact same airframe type across different operators. The Structural laggards: Older, sub-optimal fleet types like Delta’s 717 and the smaller A319s (0.68–0.73) are penalized for their lower seat counts and older engine architectures relative to the massive capacity weights of the global fleet. Mergers: Moving the Hawaiian fleet into Alaska Airlines for reporting gives a look at how newer Hawaiian A21Ns perform compared to the previous ex-Virgin America A21Ns at Alaska. Alaska Airlines Here we see the impact of Hawaiian's fleet consolidation. The 717's poor FEI drives the colors. It is materially lower than the 737-700 (73G). The MAX fleet delivers best-in-class FEI. The maligned (at Alaska) A21N is back, and its numbers are at the top. Alaska unloaded the inherited Airbus fleet as fast as it could. Looking at the last row, you see the negative drag on fleet FEI the 717 has brought. It's no surprise to see chatter in the industry about retiring them. [caption id="attachment_195256" align="aligncenter" width="470"] US DoT T2; AirInsight[/caption] American Airlines It turns out the MAX 8 is the leader at American. The Airbus fleet is outclassed as it is outdated. This fleet is in the crosshairs for the A220 or E195-E2. That's the good news; there's a solution. The bad news is neither OEM could deliver fast enough for the fleet size. That means American suffers relative fuel inefficiency for years to come. [caption id="attachment_195253" align="aligncenter" width="462"] US DoT T2; AirInsight[/caption] Delta Air Lines It's plain to see - Delta likes airplanes. Once it gets one, retiring is hard. This is the widest fleet among the US airlines. The numbers on older A19 and A320 compare with those at American. They would be red here too, but for the 717. The last data row showing the averages tells us Delta is even worse off than American. But to their credit, they moved to the A220, and it delivers good FEI. They are the only airline, as we noted yesterday, that has made this move. Another surprise - look at the 757-300 delivering excellent FEI. Olden and golden. Pity they only have 16. [caption id="attachment_195255" align="aligncenter" width="527"] US DoT T2; AirInsight[/caption] Southwest Airlines Here we see the least complex fleet among big US airlines. The results once again show how efficient the MAX is. Southwest has the largest MAX fleet and its acquisition pace remains good. If it does take the 'soon-to-be-certified' MAX 7, then the A220 has a real competitor. We are eager to see the impact of the FEI. We don't show the data here, but elsewhere we have reported on the excellent fuel burn (ASM/Gallon) from the MAX 8-200. Retiring the 737-700 at Southwest will materially impact fuel burn. [caption id="attachment_195258" align="aligncenter" width="476"] US DoT T2; AirInsight[/caption] United Airlines Here we see the second most complex single-aisle fleet. Not much green - but that which is green tells the story of how impactful an updated fleet is. Note the comparison of the 757-300 here and at Delta. Truly a remarkable aircraft, and yet so few were ordered. Here we see the impact again, and the drag, of the A319 and A320. They need to be replaced, and United is the most aggressive US airline in its re-fleeting. Every week we see new A321neo and MAX 9 going to United. This investment is going to pay off over the next two decades. [caption id="attachment_195259" align="aligncenter" width="533"] US DoT T2; AirInsight[/caption] Summary The summary chart distills the competitive reality: Frontier stands alone. An all-neo, high-density fleet isn't an operational choice — it's a structural cost advantage that compounds over time. The legacy carriers know the math. The only question is how fast they can act on it. The 2026 data is through 1Q, and we can see that, aside from Sun Country, the industry is closely matched. But that's all about to change, too. [caption id="attachment_195260" align="aligncenter" width="823"] US DoT T2; AirInsight[/caption]

US Flight Planner - US DoT On-Time Data	Airbus vs Boeing - Official OEM Data
US Airline Schedule Performance - US DoT Data	Daily OEM Production & Deliveries -

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