Worldwide orders for the smaller A320neo have been 25% higher than for the A321neo. In the USA the dominant model has been the A321neo. There have only been three orders for the A320neo, and the third one placed by Virgin America and inherited by Alaska Airlines is obviously very vulnerable.

A320neo / A321neo @Oct 2019
165 / 49 FRONTIER AIRLINES
43 / 0 SPIRIT AIRLINES
30 / 0 VIRGIN AMERICA→ ALASKA
0 / 120 AMERICAN AIRLINES
0 / 100 DELTA AIR LINES
0 / 85 JETBLUE AIRWAYS
0 / 16 HAWAIIAN AIRLINES (+2 leased A321neo)
238 / 370 All Neos

No NEO orders as of October 2019
Southwest
United
Sun Country
Allegiant

The A320ceo was more popular with USA airlines
JETBLUE AIRWAYS 132
UNITED AIRLINES 98
NORTHWEST AIRLINES 78
SPIRIT AIRLINES 55
US AIRWAYS 28
AMERICA WEST AIRLINES 23
VIRGIN AMERICA 19
ALLEGIANT AIR 13
FRONTIER AIRLINES 4

I suspect that the A321neo will get additional USA orders, but I don't know if any more A320neo orders will arrive at this point.
Any thoughts?

Legacy carriers will configure the A321neo just under 200 seats requiring 4 flight attendants Low cost carriers would be over 200 seats adding a 5th FA. Jetblue configures their A321s with 200 seats or less to avoid the extra FA. The A321neo also can fulfill transcontinental roles that the A321ceo would of had limitations on. AA has 150 seats on their A320ceo but low cost carriers have around 180 seats on theirs. In all fairness the A319 and the A320 should have been stretched by 2 frames. The A320.5 would be a perfect fit for US LCC and the A319.5 would be suited better for legacy carriers

PacoMartin wrote:

Any thoughts?

US airlines are a bit behind on replacing old types. I suspect that Delta and AAs priority was to first and foremost replace their MD-80 and 757 fleets. It is an almost perfect fit for the 757 replacement, while for part of the MD-80/90 fleets they decided to upgrade (much of the latter also got replaced by smaller 737NGs).

Eventually I could see a possibility of the A320neo at Delta, when the time comes to replace the A319ceo and A320ceo. Of course they could also split it between more A321s and A220s.
For American Airlines, they have the middle covered by the 737-8.
United, who knows. For now they seem intent on covering their needs with the 737MAX and second hand A319s. Personally I doubt it.

JetBlue should be a strong contender. The A321neo has so far only been for expansion at that airline. Eventually they will need to replace the A320 fleet.

But it doesn't really help that the US has so few airlines to begin with (independent mainline airlines at least, not counting affiliate regional operators).

VSMUT wrote:

US airlines are a bit behind on replacing old types.

There is an existing fleet of 764 aging A319/A320 ceos spread among airlines other than Frontier and Spirit which have ordered neo versions. It doesn't seem as if anyone wants to purchase newer versions of the A319 with the same size jet. Delta has the oldest individual jets with an A320 over 29 years old.

A319ceo years / count
16.31 317
18.00 80 United
17.80 57 Delta Airlines
15.50 132 American
14.40 38 Allegiant
12.10 10 Alaska

A320ceo years / count
16.93 447
24.30 62 Delta Airlines
21.40 99 United
18.50 48 American
14.2 130 Jetblue
13.1 55 Allegiant
9.20 53 Alaska (8 year old order for 30 A320neos)

CEOs you can fly till 30 and they are still profitable especially on short stints <2h. Why replace them with an existing frame at 20 years of age when you can use them for 10 more. Delta will be the first one to start replacing them but it will be interesting how. Some probably with A321 others maybe with A220 and increased frequencies if possible. Depending on what the next single aisle from A & B will be the NEO/MAX generation might be skipped (or as much as possible) and the time till then just filled by buying cheap NGs and ceos.

Well the USA always had the most B757's. These now all need to be replaced.

Keeping United from buying A321s has been a battle won by Boeing so far. With the NMA/MAX situation continuing and the A320/757s getting real old, I wonder if Boeing can keep United on board..

It should not bother Airbus to much, the rest of the world buys heaps of A320neo. Over 3000 in backlog. The problem is getting in line.
That is without counting the 2900 frames backlog for the A321neo.
That is not including the orders from Dubai.

PacoMartin wrote:

VSMUT wrote:

US airlines are a bit behind on replacing old types.

There is an existing fleet of 764 aging A319/A320 ceos spread among airlines other than Frontier and Spirit which have ordered neo versions. It doesn't seem as if anyone wants to purchase newer versions of the A319 with the same size jet. Delta has the oldest individual jets with an A320 over 29 years old.

A319ceo years / count
16.31 317
18.00 80 United
17.80 57 Delta Airlines
15.50 132 American
14.40 38 Allegiant
12.10 10 Alaska

A320ceo years / count
16.93 447
24.30 62 Delta Airlines
21.40 99 United
18.50 48 American
14.2 130 Jetblue
13.1 55 Allegiant
9.20 53 Alaska (8 year old order for 30 A320neos)

It is all very relevant, but keep in mind, there are still a couple hundred even older and less fuel efficient MD-80s and 757s in service. In a time with high fuel costs, replacing those has higher priority.

PacoMartin wrote:

Worldwide orders for the smaller A320neo have been 25% higher than for the A321neo. In the USA the dominant model has been the A321neo. There have only been three orders for the A320neo, and the third one placed by Virgin America and inherited by Alaska Airlines is obviously very vulnerable.

A320neo / A321neo @Oct 2019
165 / 49 FRONTIER AIRLINES
43 / 0 SPIRIT AIRLINES
30 / 0 VIRGIN AMERICA→ ALASKA
0 / 120 AMERICAN AIRLINES
0 / 100 DELTA AIR LINES
0 / 85 JETBLUE AIRWAYS
0 / 16 HAWAIIAN AIRLINES (+2 leased A321neo)
238 / 370 All Neos

No NEO orders as of October 2019
Southwest
United
Sun Country
Allegiant

The A320ceo was more popular with USA airlines
JETBLUE AIRWAYS 132
UNITED AIRLINES 98
NORTHWEST AIRLINES 78
SPIRIT AIRLINES 55
US AIRWAYS 28
AMERICA WEST AIRLINES 23
VIRGIN AMERICA 19
ALLEGIANT AIR 13
FRONTIER AIRLINES 4

I suspect that the A321neo will get additional USA orders, but I don't know if any more A320neo orders will arrive at this point.
Any thoughts?

B6 has a lot of old A320ceo that are comming up for replacement. There was no need to replace them when the A321neo's were being ordered as those were for expansion, not replacement. So the A320neo orders could increase, unless the A220-500 gets the green light.

rbavfan wrote:

PacoMartin wrote:

Worldwide orders for the smaller A320neo have been 25% higher than for the A321neo. In the USA the dominant model has been the A321neo. There have only been three orders for the A320neo, and the third one placed by Virgin America and inherited by Alaska Airlines is obviously very vulnerable.

A320neo / A321neo @Oct 2019
165 / 49 FRONTIER AIRLINES
43 / 0 SPIRIT AIRLINES
30 / 0 VIRGIN AMERICA→ ALASKA
0 / 120 AMERICAN AIRLINES
0 / 100 DELTA AIR LINES
0 / 85 JETBLUE AIRWAYS
0 / 16 HAWAIIAN AIRLINES (+2 leased A321neo)
238 / 370 All Neos

No NEO orders as of October 2019
Southwest
United
Sun Country
Allegiant

The A320ceo was more popular with USA airlines
JETBLUE AIRWAYS 132
UNITED AIRLINES 98
NORTHWEST AIRLINES 78
SPIRIT AIRLINES 55
US AIRWAYS 28
AMERICA WEST AIRLINES 23
VIRGIN AMERICA 19
ALLEGIANT AIR 13
FRONTIER AIRLINES 4

I suspect that the A321neo will get additional USA orders, but I don't know if any more A320neo orders will arrive at this point.
Any thoughts?

B6 has a lot of old A320ceo that are comming up for replacement. There was no need to replace them when the A321neo's were being ordered as those were for expansion, not replacement. So the A320neo orders could increase, unless the A220-500 gets the green light.

The A220-500 is indeed an interesting case for US carriers

- they use bulk load in their luggage / cargo operations anyway
- it's build in USA
- way lighter/ more efficient than 319NEO/738MAX
- offers interesting 3 fa seatcapacity / CASM with typical US 2 class configurations.

VSMUT wrote:

But it doesn't really help that the US has so few airlines to begin with (independent mainline airlines at least, not counting affiliate regional operators).

The DOT's Air Travel Consumer Report covers ten mainline carriers, the smallest of which by frame count is Hawaiian at 60 aircraft. Sun Country is a little less than half that size. How many is the right number?

To the OP's thesis:

DL upgauged and bought 739s and 321s instead of direct A320 replacements. They've shown the math on CASM for large narrowbodies vs. medium narrowbodies.

AA went with 738s (and later MAX 8s) for their mid-size narrowbody while Airbus got the small and large with AA's blow-out narrowbody orders of 460 frames in 2011. Planespotters.net shows AA with 304 738s at an avg age of 10.1 years. https://www.nytimes.com/2011/07/21/busi ... akers.html

UA hasn't gotten around to replacing 320s. MAX 9 and 10 orders suggest a MAX 8 if they want parts/crew efficiencies but they may seek to balance manufacturers. UA's oldest 320 is 26 years old, and a subfleet avg of 21.4 years, so a plan will soon unfold. Whether it's a direct 320neo or MAX 8 replacement, or they upgauage (lots of Max 10s and 9s on order already), remains to be seen.

The 320s of Alaska and JetBlue aren't old enough to worry about replacing. Spirit's are even newer still.

Given those facts and circumstances I don't see anything particularly anomalous about a present absence of 320neo orders by U.S. carriers.

The US economy is strong with increasing passenger demand. In a strong domestic market, airlines want bigger planes so that they can upgauge flights to adjust to demand which led to a surge in demand for A321s and 737-900ERs. In a weak economy, we see that smaller airplanes are more popular. US airlines don’t always replace airplanes one for one. When the economy is strong they upgauge when retiring airplanes. When the economy is weak like it was in the 2000s, airlines downgauge and buy smaller planes.

FluidFlow wrote:

CEOs you can fly till 30 and they are still profitable especially on short stints <2h. Why replace them with an existing frame at 20 years of age when you can use them for 10 more. Delta will be the first one to start replacing them but it will be interesting how. Some probably with A321 others maybe with A220 and increased frequencies if possible. Depending on what the next single aisle from A & B will be the NEO/MAX generation might be skipped (or as much as possible) and the time till then just filled by buying cheap NGs and ceos.

While an A320 can fly for 30 years, most do not. More than 75% of A320s are scrapped before they hit 30 years. 757s actually have a longer average useable life in service than A320s based on age at retirement

Air Travel Consumer Report CARRIER* NUMBER OF AIRPORTS REPORTED

UNITED AIRLINES NETWORK 237
- UNITED AIRLINES 107
- BRANDED CODESHARE PARTNERS 220
AMERICAN AIRLINES NETWORK 238
- AMERICAN AIRLINES 106
- BRANDED CODESHARE PARTNERS 221
DELTA AIR LINES NETWORK 225
- DELTA AIR LINES 143
- BRANDED CODESHARE PARTNERS 201
ALLEGIANT AIR 110
FRONTIER AIRLINES 102
ALASKA AIRLINES NETWORK 97
- ALASKA AIRLINES 72
- BRANDED CODESHARE PARTNERS 53
SOUTHWEST AIRLINES 88
JETBLUE AIRWAYS 67
SPIRIT AIRLINES 50
HAWAIIAN AIRLINES NETWORK 22
- HAWAIIAN AIRLINES 19
- BRANDED CODESHARE PARTNERS 4
TOTAL AIRPORTS SERVED 367

MIflyer12 wrote:

The DOT's Air Travel Consumer Report covers ten mainline carriers, the smallest of which by frame count is Hawaiian at 60 aircraft. Sun Country is a little less than half that size. How many is the right number?

The consumer report states: *All U.S. airlines with at least 0.5 percent of total domestic scheduled service passenger revenues plus any branded codeshare partners.
which cuts off Sun Country from the list
Domestic scheduled service by passengers for 2018
10,031,000 Hawaiian Air
2,089,000 Sun Country

First half 2019 total revenue
$23,073 Delta Air Lines Inc.
$22,539 American Airlines Inc.
$20,991 United Air Lines Inc.
$11,059 Southwest Airlines Co.
$4,161 Alaska Airlines Inc.
$3,977 JetBlue Airways
$1,869 Spirit Air Lines
$1,368 Hawaiian Airlines Inc.
$1,184 Frontier Airlines Inc.
$897 Allegiant Air
$366 Sun Country Airlines d/b/a MN Airlines

FluidFlow wrote:

CEOs you can fly till 30 and they are still profitable especially on short stints <2h. Why replace them with an existing frame at 20 years of age when you can use them for 10 more. Delta will be the first one to start replacing them but it will be interesting how. Some probably with A321 others maybe with A220 and increased frequencies if possible. Depending on what the next single aisle from A & B will be the NEO/MAX generation might be skipped (or as much as possible) and the time till then just filled by buying cheap NGs and ceos.

Lol i was about to write the same, anyway thanks for reading my mind

Weatherwatcher1 wrote:

The US economy is strong with increasing passenger demand. In a strong domestic market, airlines want bigger planes so that they can upgauge flights to adjust to demand which led to a surge in demand for A321s and 737-900ERs. In a weak economy, we see that smaller airplanes are more popular. US airlines don’t always replace airplanes one for one. When the economy is strong they upgauge when retiring airplanes. When the economy is weak like it was in the 2000s, airlines downgauge and buy smaller planes.

FluidFlow wrote:

CEOs you can fly till 30 and they are still profitable especially on short stints <2h. Why replace them with an existing frame at 20 years of age when you can use them for 10 more. Delta will be the first one to start replacing them but it will be interesting how. Some probably with A321 others maybe with A220 and increased frequencies if possible. Depending on what the next single aisle from A & B will be the NEO/MAX generation might be skipped (or as much as possible) and the time till then just filled by buying cheap NGs and ceos.

While an A320 can fly for 30 years, most do not. More than 75% of A320s are scrapped before they hit 30 years. 757s actually have a longer average useable life in service than A320s based on age at retirement

A320 just entered service 30 yrs ago & 757 hasn't been build for 15 years & there was no replacement.
But probably you liked the conclusion so much, you took a short break from integrity on the data

MIflyer12 wrote:

VSMUT wrote:

But it doesn't really help that the US has so few airlines to begin with (independent mainline airlines at least, not counting affiliate regional operators).

The DOT's Air Travel Consumer Report covers ten mainline carriers, the smallest of which by frame count is Hawaiian at 60 aircraft. Sun Country is a little less than half that size. How many is the right number?

Wikipedia shows eleven, I'm not saying anything is right or wrong.

But 11 is not many*. Consider that of those 11:
3x already have it (Alaska, Frontier and Spirit)
3x are die hard 737 or have no need for that size of plane (Southwest, Sun country and Hawaiian)
Then you are already down to just 5 candidates. And 2 of those (UA and AA) have already committed to an aircraft of that size.
That leaves a mere 3 possibilities: Delta, Allegiant and JetBlue.


*For comparison, just on a quick count I get independent 27 airlines with own ticket sales in Europe, and that is counting IAG, LH Group, AF-KLM and a few other groups as one and omitting some pretty relevant Turkish and Russian carriers.

keesje wrote:

The A220-500 is indeed an interesting case for US carriers

- they use bulk load in their luggage / cargo operations anyway
- it's build in USA
- way lighter/ more efficient than 319NEO/738MAX
- offers interesting 3 fa seatcapacity / CASM with typical US 2 class configurations.

That's not a typical US 2-class configuration. Typical US legacy configuration is 2.5 class with 36-37" F seat pitch, several rows regular Economy of 34-35" seat pitch, and then the rest 30-31". In that hypothetical size, ignoring FA constraints you'd be looking at more like 160 seats, not 148. I could see that being an interesting decision point (150 seater with high amount of premium seating - probably less F and more Y+ though).

ethernal wrote:

keesje wrote:

The A220-500 is indeed an interesting case for US carriers

- they use bulk load in their luggage / cargo operations anyway
- it's build in USA
- way lighter/ more efficient than 319NEO/738MAX
- offers interesting 3 fa seatcapacity / CASM with typical US 2 class configurations.

That's not a typical US 2-class configuration. Typical US legacy configuration is 2.5 class with 36-37" F seat pitch, several rows regular Economy of 34-35" seat pitch, and then the rest 30-31". In that hypothetical size, ignoring FA constraints you'd be looking at more like 160 seats, not 148. I could see that being an interesting decision point (150 seater with high amount of premium seating - probably less F and more Y+ though).

And they certainly will not be putting 28 F seats in them, but rather 12-16. 28 is more than used on A321s/757s. US airlines are densifying their A320/738 cabins to be around 160-170 seats as you say. Many had 4 FAs anyways for service reasons and it makes it easier on crew scheduling with larger narrow bodies that will need 4 FAs.

Weatherwatcher1 wrote:

While an A320 can fly for 30 years, most do not. More than 75% of A320s are scrapped before they hit 30 years. 757s actually have a longer average useable life in service than A320s based on age at retirement

32.1 Years oldest active passenger B757 which is due to be retired in the next few weeks flown by Jet2 | 36.9 years first delivery of B757
30.9 Years oldest active passenger A320 | 31.7 years firsts delivery of A320

I am not sure how much data you have to support that sweeping generalization.

The ages are similar for the three USA carriers

United Fleet
99 Airbus A320 21.40 years
74 Boeing 757 21.70 years

Delta fleet
62 Airbus A320 24.30 years
127 Boeing 757 22.30 years

American fleet
48 Airbus A320-200 18.50 years
34 Boeing 757-200 19.90 years

PacoMartin wrote:

Weatherwatcher1 wrote:

While an A320 can fly for 30 years, most do not. More than 75% of A320s are scrapped before they hit 30 years. 757s actually have a longer average useable life in service than A320s based on age at retirement

32.1 Years oldest active passenger B757 which is due to be retired in the next few weeks flown by Jet2 | 36.9 years first delivery of B757
30.9 Years oldest active passenger A320 | 31.7 years firsts delivery of A320

I am not sure how much data you have to support that sweeping generalization.

The ages are similar for the three USA carriers

United Fleet
99 Airbus A320 21.40 years
74 Boeing 757 21.70 years

Delta fleet
62 Airbus A320 24.30 years
127 Boeing 757 22.30 years

American fleet
48 Airbus A320-200 18.50 years
34 Boeing 757-200 19.90 years

My statement that most A320s do not fly for 30 years was 100% factual and is supported by statistics

• 77% of 757s built in 1989 (30 years old) are still in service
• 22% of A320s built in 1989 (30 years old) are still in service

keesje wrote:

Weatherwatcher1 wrote:

The US economy is strong with increasing passenger demand. In a strong domestic market, airlines want bigger planes so that they can upgauge flights to adjust to demand which led to a surge in demand for A321s and 737-900ERs. In a weak economy, we see that smaller airplanes are more popular. US airlines don’t always replace airplanes one for one. When the economy is strong they upgauge when retiring airplanes. When the economy is weak like it was in the 2000s, airlines downgauge and buy smaller planes.

FluidFlow wrote:

CEOs you can fly till 30 and they are still profitable especially on short stints <2h. Why replace them with an existing frame at 20 years of age when you can use them for 10 more. Delta will be the first one to start replacing them but it will be interesting how. Some probably with A321 others maybe with A220 and increased frequencies if possible. Depending on what the next single aisle from A & B will be the NEO/MAX generation might be skipped (or as much as possible) and the time till then just filled by buying cheap NGs and ceos.

While an A320 can fly for 30 years, most do not. More than 75% of A320s are scrapped before they hit 30 years. 757s actually have a longer average useable life in service than A320s based on age at retirement

A320 just entered service 30 yrs ago & 757 hasn't been build for 15 years & there was no replacement.
But probably you liked the conclusion so much, you took a short break from integrity on the data

If you don’t like the 30 year benchmark since the A320 was just entering service in 1989, you can use the 25 year benchmark and my statement is still true and supported by statistics

• 58% of A320s built in 1994 (25 years old) are still in service
• 82% of 757s built in 1994 (25 years old) are still in service

Most A320s do not have a 30 year useable life. They are retired earlier than that

mjoelnir wrote:

It should not bother Airbus to much, the rest of the world buys heaps of A320neo.

I expect Airbus is happy that the US carriers are favoring the A321 since it brings in higher revenues and margins.



As the A321 has grown in performance, the A320 might no longer be something the US carriers feel they need. An A321 can do transcons now at full payload without worry and I expect the trip cost delta between an A320 and A321 is low enough that even if they have to sell some of those extra seats at a discount to fill them, the incremental revenue is more than the incremental costs.

mjoelnir wrote:

It should not bother Airbus to much, the rest of the world buys heaps of A320neo. Over 3000 in backlog. The problem is getting in line.
That is without counting the 2900 frames backlog for the A321neo.
That is not including the orders from Dubai.

Why should this even bother AIrbus at all? More airlines buying the A321neo over the A320neo means more revenue. Airlines in the USA can buy 100% A321neo for all they care. Airbus will be delighted!

keesje wrote:

Weatherwatcher1 wrote:

A320 just entered service 30 yrs ago & 757 hasn't been build for 15 years & there was no replacement.
But probably you liked the conclusion so much, you took a short break from integrity on the data

If you don’t like the 30 year benchmark since the A320 was just entering service in 1989, you can use the 25 year benchmark and my statement is still true and supported by statistics

• 58% of A320s built in 1994 (25 years old) are still in service
• 82% of 757s built in 1994 (25 years old) are still in service

Most A320s do not have a 30 year useable life. They are retired earlier than that

I'm not disputing your data but the conclusion you're drawing from it (i.e. the A320 is not as durable as the 757) is simply wrong. Two key reasons:

1. The 757 fly longer sectors on average than the A320. This means lower cycles and airframe life is measured primarily in cycles
2. A320s are retired earlier because more efficient replacements are already available, and that it makes sense commercially to do so, not because they're technically not capable of flying as long, whereas the 757 viable replacements are only just starting to become available

Weatherwatcher1 wrote:

PacoMartin wrote:

I am not sure how much data you have to support that sweeping generalization.

My statement that most A320s do not fly for 30 years was 100% factual and is supported by statistics

• 77% of 757s built in 1989 (30 years old) are still in service
• 22% of A320s built in 1989 (30 years old) are still in service

My question was more about how much data you had, then the accuracy of the statement. According to planespotters, Delta has only 4 B757s over age 30, and United has only 1. As you pointed out the majority of the B757 (roughly 70%) were delivered to USA companies.
If you have an accurate database, can you tell us how many of those 77% are working as cargo jets?

The Boeing database indicates 255 deliveries from 1982-1989. A total of 77% of 255 is 196 active B757s.

B757-200
1982 2
1983 25
1984 18
1985 36
1986 35
1987 35
1988 37
1989 50
757-200M
1988 1
757-200PF
1987 5
1988 10
1989 1

Perhaps I misunderstand your statistic. Do you mean 77% of B757s actually built in the year 1989? So you are talking about roughly 50 jets.


The A320s that are older than 29 years old had a slightly smaller engine which I believe was less efficient.
A320-111 26 February 1988 CFM56-5A1~ 25,000 lbf
A320-211 8 November 1988 CFM56-5A1~ 25,000 lbf
A320-212 20 November 1990 CFM56-5A3~ 26,500 lbf

VSMUT wrote:

United, who knows. For now they seem intent on covering their needs with the 737MAX and second hand A319s. Personally I doubt it.

United's smaller narrowbody fleet is so old, and they have purchased so few smaller jets in the last decade that I suspect that their "needs" must change in the next decade.

597 United Airlines NBs 15.78 years
80 Airbus A319 18.00 years on average
99 Airbus A320 21.40
74 Boeing 757 21.70
41 Boeing 737-700 20.6
141 Boeing 737-800 15.8
148 Boeing 737-900 7.9
14 Boeing 737 MAX 9 1.2

PacoMartin wrote:

VSMUT wrote:

United, who knows. For now they seem intent on covering their needs with the 737MAX and second hand A319s. Personally I doubt it.

United's smaller narrowbody fleet is so old, and they have purchased so few smaller jets in the last decade that I suspect that their "needs" must change in the next decade.

597 United Airlines NBs 15.78 years
80 Airbus A319 18.00 years on average
99 Airbus A320 21.40
74 Boeing 757 21.70
41 Boeing 737-700 20.6
141 Boeing 737-800 15.8
148 Boeing 737-900 7.9
14 Boeing 737 MAX 9 1.2

But they will also be adding over 160 new and secondhand aircraft, probably a fair few more. According to Wikipedia, they are now beginning to take some Vueling A320's too. They can continue finding fairly good used A319s and A320's for a decade at least. 737-800s as well.

VSMUT wrote:

But they will also be adding over 160 new and secondhand aircraft, probably a fair few more. According to Wikipedia, they are now beginning to take some Vueling A320's too. They can continue finding fairly good used A319s and A320's for a decade at least. 737-800s as well.

United purchases an average of two new Boeing aircraft a month for the last 8 years. Their fleet of widebodies is 40 more than Delta and American. They invest heavily in the -900ER and MAX-9 size narrowbody. And as you point out they keep finding used smaller jets to keep their fleet going.

There are no easy answers. American spent billions and now has their average age of their 787 narrowbody jets down to 10.76 years, younger than 750 jets in Southwest's fleet which has an average age of 11.72 years. But the financial performance of American is the worst of the big 4 airlines.

Delta seemed to revel about how good they were at maintaining old jets which they credited as an important part of their comeback from bankruptcy to the most profitable of the USA airlines. But now they are investing heavily in small jets like the A220.

United seems to be becoming the new Delta in terms of scouring the globe for older small jets to keep their fleet going.

Inevitably comes the question if airlines have simply outgrown the smallest jet sizes. I think that is a valid question, but these extended networks require small jets.
United fleet of 361 smaller jets is now 18.37 years old (B737-700/800 ; A319/320). I don't know if they can keep this fleet size operable finding used jets, and it will take more than a decade and a lot of money to replace.

I firmly believe that the primary airlines are going to shrink network size in the future allowing Frontier, Spirit and Allegiant to expand.

Airports served by mainline carriers in recent month
DELTA AIR LINES 143
UNITED AIRLINES 107
AMERICAN AIRLINES 106
ALLEGIANT AIR 110
FRONTIER AIRLINES 102
SOUTHWEST AIRLINES 88
ALASKA AIRLINES 72
JETBLUE AIRWAYS 67
SPIRIT AIRLINES 50
HAWAIIAN AIRLINES 19

Southwest sells itself as the "People's Airline" in that it is mostly point-to-point flights and there is no premium seating. But their decision to limit themselves to 88 domestic airports allows them to function without a jet smaller than 143 seats. In the USA 88% of domestic boardings are at only 61 airports which are at least 0.25% of the total traffic apiece.

Southwest's small Texas airports are a legacy of their startup in the 1970s. Mostly Southwest ignores the rural and small city population.

ELP El Paso
MAF Midland
LBB Lubbock
AMA Amarillo
CRP Corpus Christi
HRL Harlingen