Lucerne-Interlaken Express; how to then get to Zurich

Gilbert, you need to keep this simple. You want to get from A to B, A=Interlaken, B=Zürich Airport (NOT Zürich city centre).
All rail routes in Switzerland have at least one train per hour, two on the main routes, so yes you can get from anywhere to anywhere in Switzerland.

Go to the SBB (Swiss Federal railways) website: https://www.sbb.ch/en
Enter From: Interlaken (West or Ost, there are two stations in the town), to : Zürich Flughafen (the name of the station at the airport), plus date and time.
Click on "Search".
It will list all the possible trains for the next two hours. Lots, two trains per hour. Depending on train it takes about 2 h 12 mins.
The route is Interlaken, Spiez, Bern, Olten, Zürich Flughafen. The first part to Spiez is along a lake and scenic, less so thereafter.

P.S. I would not call Luzern to Interlaken an Express. It is a scenic route, beside lakes and over the Brünig Pass, but not fast.

Chris:
First, I did want to take the scenic route to the airport, and that is the name of that "express" train that goes that way.
I know that it is not an express, nor did I name it that way.
All I wanted was info to get to the airport once in Lucerne.
But I will look at the link you provided.
thanks.

Gilbert&Tina. I was a bit confused as to what you were wanting to do.
Luzern to Zürich airport is 70 minutes. A quick trip across the (relatively) flat part of Switzerland and through the Zürich conurbation.

Luzern to Interlaken is 1h50 in TOTALLY THE OPPOSITE DIRECTION.
See map of Switzerland here: https://www.sbb.ch/content/dam/infrastruktur/trafimage/karten/karte-sts-pass-gueltigkeit.pdf
This is a scenic route, past lakes and over the Brünig Pass, so it is usually called the Brünig Pass Route. I has one train per hour. It is marketed as the "Luzern–Interlaken Express", but is not a special tourist train, it is the same regular hourly train the locals take.

If you then want to get from Interlaken to Zürich airport, you can either double back the way you came via Luzern. or take the longer but slightly faster route via Bern and the lowlands, which takes just under 2½ hours.

CONCLUSION: Luzern - Interlaken - Zürich airport takes 4h10. Luzern - Zürich airport direct takes 70 minutes. Going via Interlaken is not logical. If you want to go this route, do it out-and-back as a day trip from Luzern on a different day.

I believe the question is Interlaken Ost > Brünig > Luzern > Zürich Flughafen.

Once you have had sufficient Luzern you board the train to the airport. There are two trains an hour from Luzern to Zürich and one of them continues to the airport. If you get the one which doesn't you can change in Zürich for the correct one.

While it does take longer than the flatland route it is quite scenic, one of my favs. The train changes ends in Meiringen which is at the end of a long two pronged fork. If you were going forward you will go backward and vice versa.

I'd never seen the Lucerne-Interlaken Express marketing title, I've always called it the Brünig route. You will also see the whole route from Luzern to Montreux marketed as the Golden Pass Route. It is all the same, just the occasional extra fare fancy tourist trains are mixed in with the regular ones.

My understanding of your question is that you are traveling from Interlaken to the Zurich airport, taking the scenic "Luzern-Interlaken Express" train which ends in Luzern, and then you want to change in Luzern to the train that goes directly to the Zürich airport (Flughafen).

I noticed last summer that the scenic Brunig Pass route (which is via Meiringen) had the new name "Luzern-Interlaken Express" written on the side of its train carriages, and I see on the SBB transportation web site that they name it that way, now, too. (It used to say "Golden Pass" on the side of the train cars.)

The "Luzern-Interlaken Express" always pulls into the Luzern station on Platform 12 at 55 minutes after each hour.
The train you want from Luzern to the Zurich airport (Flughafen), which doesn't require you changing trains along the way, dragging your luggage, is the direct train that always leaves from Luzern's Platform 4 at 10 minutes after each hour.

By the way, I took the "Luzern-Interlaken Express" many times last summer, and those trains are new and very nice. They have panorama windows. The restrooms are unusually roomy. And they have a Bistro Car with table service. The rows of seats have a little table by each window, too.