United Airlines is a major force in the US domestic market. Known for its slogan, "Fly the Friendly Skies," the airline has been around for quite some time. Over the years, a number of planes have entered and exited the airline's fleet. Here is a look at the oldest aircraft still flying for United Airlines.

Boeing 757s and 767s take the top spots

United's most aged planes are the Boeing 757s and 767-300ERs, according to data from Planespotters.net. The two oldest planes are Boeing 757s. N502UA is 31 years old, while N521UA is 30 years old.

Next up are 13 Boeing 767-300ERS:

1. N641UA (29 years old)
2. N642UA (29 years old)
3. N644UA (29 years old)
4. N643UA (29 years old)
5. N646UA (28 years old)
6. N647UA (28 years old)
7. N648UA (28 years old)
8. N649UA (28 years old)
9. N651UA (28 years old)
10. N652UA (28 years old)
11. N653UA (28 years old)
12. N654UA (28 years old)
13. N655UA (28 years old)

This is also followed up by eight 27-year-old 767-300ERS. There are also three older 757-200s: N568UA (28 years old), and two 27-year-old 757s, N87UA, and N588UA.

All of these planes came new to United Airlines and have served venerably in the carrier's fleet. The 767-300ERs are used on a variety of routes. Some of them operate transcontinental flights out of Los Angeles to major hubs, including Newark and Washington-Dulles, and on smaller-demand international flights to destinations like Venice, Manchester (previously), Berlin, and others.

The 757s fly some transcontinental service. However, these planes also do smaller international routes such as between Newark and Lima, Dulles to Dublin, and Chicago to Edinburgh.

The Airbus A320s

In the 1990s, United Airlines started taking on Airbus A320s. This was a departure from the carrier's strong Boeing fleet. The airline has 21 A320-200s that are 26 years old. These are registered as N401UA through N421UA.

The Airbus A320s are part of United's short-haul fleet. The airline is working on retrofitting these aircraft with more first class seats as part of a push for premium customers.

What is the fate of these aircraft?

The fate of these planes remains up in the air. The airline is managing the current crisis and attempting to chart the best course forward. It is unclear if some of these older planes will return to service.

The A320s are likely to remain in service while some of the 767s and 757s could be on their way out. While some of the 757s have returned to service, many remain parked. Most of the aircraft mentioned above remain parked, currently.

United is still actively monitoring the situation and altering its fleet plans as necessary. Much of the airline's future plans will likely depend on when the carrier sees demand coming back. When the airline ordered new A321XLRS, it was planning on using them for transatlantic services out of Newark and Washington. This would see the Airbus A321XLR work as an ideal 757 replacement.

While the A321XLRs aren't due at the carrier until 2024 onwards, the airline has to decide whether or not it is viable to continue flying its current 757 routes. The fewer 757 routes the airline operates, the more 757-200s it would likely retire.

What is the oldest United plane you've flown on? Let us know in the comments!