Auckland to LA is a little over 12 hours. But, in my case, total flight time was almost 20 hours because the plane had to turn back twice because of an electrical problem. They had to dump the fuel so that was an extra hour on the first two attempts. Finally made it back to LA a day late.
Don’t remember how long it took, but I flew from Tokyo to Frisco once.
Damn, the longest flight i’ve ever taken was 4 hours. And even that was mildly unpleasant. I can’t sleep on a plane, so a 12 or 16 hour flight would not be pleasant at all. It beats the alternatives though.
The one that *felt *the longest was a Delta flight that was supposed to be Washington Dulles -> Atlanta -> San Jose, but because another Delta flight was grounded, they decided to reroute us to pick up the passengers on the other flight. So we wound up Washington Dulles -> Atlanta -> New Orleans -> Shreveport -> Los Angeles -> San Jose. All of those wait times on the ground felt like forever.
I’ve done London - Hong Kong and Auckland - LA. Both about 12 hours.
To be honest I don’t mind it so much. Even in economy, As long as I’m fed, watered and entertained I’m happy as Larry.
I don’t sleep on a plane so a flat bed would be wasted on me. When you chunk it up it isn’t too much of an issue really. Think of it as three movies interspersed with 3 meals and a few sessions with a good book. If you are one of the lucky ones who can sleep. then you are golden.
I’ve done JFK to Singapore - 21 hours non-stop.
I barely remember my longest. Clarksville, TN to the Marshall Islands when I was 3.
The longest I DO remember was Chicago to Warsaw, Poland. 9 hours, 51 minutes.
Japan to San Francisco, non stop.
The first time I did Detroit-to-Tokyo (~13.5 hrs), I was in a mildly anxious state by the end of the flight. I had never done one nearly that long before, and between the sleep deprivation and the lack of preparedness with respect to in-flight entertainment, it was an emotional feeling of “I may never be allowed out of this box.”
Now knowing what to expect, subsequent flights have been anxiety free, although I generally don’t sleep. But with the seatback entertainment system, along with a laptop PC stuffed with several gigabytes of TED talks, I have plenty of material to keep my brain occupied. Apart from that, it helps to drink a LOT of water during the flight (wife and I each buy a liter before departure, and the cabin crew also gives you water between meals); this makes you get up to pee about once per hour, which is good for your body. After I’m done peeing, I stand in the bathroom for a minute and do calf raises and other leg- and buttock-tensing exercises to get blood flowing all through my lower body; deep vein thrombosis is a real concern on long-haul flights like that, and thorough hydration and occasional leg exercise goes a long way toward preventing it.
You undoubtedly remained on the same plane, but you stopped somewhere…I don’t believe any commercial airline can fly 21 hours non-stop.
Longest single leg: New York to Johannesburg, ~18.
Longest combined flights: Portland to Phnom Penh and the reverse, typically ~32.
Dubai to Sydney 13 hours 35 minutes
But that’s only part of the flight from Manchester to Christchurch, New Zealand. The entire journey is usually over 30 hours.
It was more than 20 years ago, but flying from JFK to Narita we had an aborted takeoff due to an erroneous instrument reading. 747 taxied back to the terminal. We sat on the plane as it was checked out and eventually took off two hours late. When we finally got to Japan, we had to circle at least an extra half hour waiting for a landing slot. I think I was on the plane at least 16 hours, maybe longer.
The flight with the most air hours was probably LAX-SYD, back in the day. And I don’t think (???) that we got out of the plane for refuling in HNL
But back in the day, economy wasn’t full, and we were smaller anyway. I slept on the floor.
You are indeed correct. I am confusing a Samsung smartphone with a luxury-class business jet. (Jeesh, how embarrassing). Sad but true, but old-age does have effects on memories. 
My apologies for the confusion.