Delta would use old aircraft on this route

Delta uses old aircraft on most of their routes. That's been their MO for a while. Delta was the launch customer for the DC-9 in 1965 and retired the type in 2014. COVID accelerated the retirement of the derivatives (MD-80/90), but they're still flying the 717 (a.k.a. MD-95).

The last time I flew SFO-JFK I was on a Delta 767-400 and yeah Delta hasn't updated the interiors on those. Compared to other airlines that typically run a premium (single aisle) product on that route the extra aisle and the 2-3-2 seating are pretty competitive unless you're jonesing for crappy seat back entertainment.

Delta actually retired its DC-9s in 1993. Then it merged with Northwest Airlines in 2008 which reintroduced the DC-9 to the Delta brand, and those aircraft hung on until 2014.

I don’t know about most of their routes but likely most of their long hauls.

Only 20% of their fleet today are 757s and 767s (and they are the largest operator for both), but they are also the largest operator for the Bombardier/Airbus A220 — my favorite short haul plane, which is an engineering marvel and a new design.

A lot of the MDs were from the Northwest Airlines days which they merged with. I used to fly NWA and the cabins were never inspiring but the points never expired and were among the best in the industry.

https://en.m.wikipedia.org/wiki/Delta_Air_Lines_fleet

I used to live at a place where the airport was serviced exclusively by the MD-80. That is possibly the worst aircraft I've ever experienced. The noise, the vibration, is just awful. You can't even hear the flight attendant ask if you would like something to drink.

Delta kept that plane around in passenger service far, far too long. It should have been banned from the skies long ago.

I rejoiced when I found out the MD-80 was retired due to reduced demand from COVID. Apparently some South American carriers still use it for passenger service, so I guess I'll just have to wait a few more decades before I can be fully safe from having to experience that misery.

This is a strength of theirs. They have a very strong maintenance program called TechOps

A lot of new aircraft don't even even have back seat entertainment anymore. Just movies that stream over wifi to your phone or tablet.

They have 127 Boeing 757s, a plane that stopped being made two decades ago with still no clear successor.

I think Airbus is trying to position the A321-XLR as replacment of the 757

As does Icelandair.

I wonder if this is a general phenomenon with Delta's codeshare partners: I flew on a KLM 747-400 that looked like it came right out of the 1990s a couple of years ago. I think they've retired it since, but it was very surprising to step onto.

The 747-400 was retired not long after you flew it, I think KLM was the last airline flying passenger flights on the type and they retired it in early 2020. In general if it's getting retired soon (or primarily being used on not-so-profitable routes) it's unlikely to get any interior updates. In fact United's 747s were pretty ratty by the end (not that United is known for having nice interiors).

Lufthansa is still flying the 747-400 with passengers today (and other 747 models).

They’re also still flying the A380 and A340.

And the first class on both of those planes is amazing.

KLM have fairly new aircraft, on average.

Is the single aisle a 4-4 then?

3-3 in back probably 1-1 and 2-2 up front. American, United, and (maybe?) JetBlue use narrow bodies (757, A321) with a more premium seating configuration on SFO/LAX-JFK routes. Delta does not. True to form Delta puts pretty much anything they can find on that route (including the 767-400).

I think there are 'old aircraft' and old aircraft. A 767 is an example of the former, whereas a Caravelle would be an example of the latter. Aircraft undergo stringent inspections every x hours, have to comply with Airworthiness Directives (ADs), and even more stringent standards and practices as far as maintenance goes. That's even truer for commercial airliners. So the chronological age of a plane is usually not a great indicator of its true state.

For example, I prefer flying on a 757 to a 737, even a new one, despite the fact that 757s are no longer produced: they have fantastic performance, and a well-maintained 757 is a very good plane to fly in, despite its age. Ditto for the 767. It's a beautiful twin-aisle plane, and I recently flew on one from Atlanta, and loved the comfortable ride. In fact, I was overjoyed to discover that I'd get another opportunity to fly on a 767, having flown on one to Hawaii (Hawaiian used to operate 767s also) some years ago. I would prefer flying on an (older) 767 to even a 757. If the airline does maintenance properly and has a good safety record, then it's actually better to fly a older airplane because it is likely to be more comfortable, powerful, and safer.