I had a portable I used at night when I went to Australia, and I used it (battery or dc power) on the domestic and in state flights here and there, but I rented the oxygen for crossing the ocean because I wanted to make sure I had it, in case the concentrator messed up.
It cost me $600 or a bout that for my rental cylinders, because thy charge $100 a cylinder and they last about 7-8 hours.

So can he have a concentrator waiting for him to sleep under and rent the rest from the planes, or can he locate a dependable portable concentrator to use on the flight, and at night?
It would have to be continous flow, but could do pulse on the plane.
I believe Gwapo went thru a similar thing, so he had his doctor do an altitude test to see how low his o2 dropped when the plane would reach crusing altitude, and it showed he did not need it.

So has his doctor given him an altitude test? Have him check with the airlines what concentrators they allow, and make sure he checks out every flight, because some have quit allowing that.
Have his doc do an altitude test to make sure he needs it in flight, and if so he needs to download airlines medical papers to get doctor to sign.
Brenda
ps, at that time I was only on O2 at night also, but the altitude test showed my o2 dropping to 80 or below.....

I just went on a cruise and I need oxygen at night. My oxygen supplier exchanged my stationery concentrator for a solo portable concentrator that I used for my trip. I understand that the solo is approved for flying and your airline may allow you to bring it aboard. This POC is capable of providing 1-3 LPM continuous flow so you probably can use it at night

thanks! I will pass this along. It mostly sounds like it's gonna cost him to get his oxygen.

I think he did all the tests. He told his doctor he was going. And he talked to the airlines about what he needs. He was mostly hoping there was a less expensive way.