I'll just call that "incredible".

Couple of data points:

I have flown JFK to Taipei/hk/Bkk via Eva air for last few yrs, always use Cpap inflight without issue. Once in a while on ANA, which does require a 24 hr notice.

Last month Eva flight delayed so switched to. CX flying Hk/JFK, dreaded sleeping without my hose, guess what - plugged it in, put on my mask and slept 7 hrs without incident!:)

On recent UA flight to Tokyo, FA came over after I slept and we traded info re Cpap models and masks. He flies with one for past 15 yrs.

I am in business class, Ymmv.

A few years ago there was no problem using a CPAP on-board, then they insisted on contacting the airline and using a battery, now its possible to just plug in again. I am thinking that F.A. comments might be a function of which class one is flying. I have flown six flights in F without a battery with no problems or comments whatsoever. I just plug in and pull the duvet over my head.

Total ignorance, battery is MORE POTENTIAL FOR FIRE than just plug it in the power outlet. What's wrong with them? Don't they at least do some research before making dumb rules?

Lugging that battery and charger around was a PITA. It also wasn´t cheap to purchase.

I tried the "call for pre-clearance" policy on a recent flight in first class from London to Hong Kong.

The good:
I used my CPAP machine inflight without being accosted by the flight crew. I plugged in and had a great snooze without incident.

The bad:
Getting clearance was a painful ordeal.
My journey to on-board sleep started when I called CX reservations and spent close to 30 min on hold. The agent who eventually answered had absolutely no idea what I was talking about and had to speak to a supervisor. Another 10 minutes on hold. Then the agent came back asking me to spell out CPAP in long form. He then disappeared for another 10 minutes and the call dropped. 50 minutes on the bloody phone and still no further along. I thought they may call me back or send me an email, but nothing.

I called again and waited 20 minutes before giving up.

The next morning I called in again and waited 15 minutes before getting an agent. Again, no idea what I was talking about and no record of my call the day before. Better prepared this time, I helped the agent navigate to the spot on the CX website where they publish CPAP information. Back on hold for 10 minutes, agent back on the line to ask more questions, back on hold for 10 more minutes, more questions. Finally the agent came on and asked if I could use a battery of if I had to plug in to the aircraft power. I don't have a battery, so I said power. He replied that if I told him I would use a battery, he could approve. So I did. (very Hong Kong way of approaching the rules).

Update: I called CX reservations for cpap clearance on my next flight and was told that it is no longer necessary to get permission as long as the Cpap unit does not use the aircraft's power supply. Happy days. Let's see what happens onboard!

My 'hope' is the left hand doesn't know what the right hand is doing. Plug it in and see what happens. Good luck!

July Update
 

Interesting call with USA toll free customer service number. She was extremely knowledgable, professional and cleared me for upcoming trip with approval to use power source. She did ask if I had battery backup in case power plug not working; I said yes, LOL :)

Took 5 minutes. Will report back if I encounter any problems.

CX 841 on Thursday went smoothly. Plugged in my S8 and slept a few hours without any problems. Chief Purser actually woke me up to 'ask if the power' outlet was working properly????

Interesting
 

I was on a long haul CX flight this week and saw three biz class passengers using CPAP (including me). And two were plugged in to the aircraft power supply. I bought an expensive battery powered unit to comply with the ever-changing rules, which appear to have either changed again or at least are not uniformly applied.

Not CX specific, I bring my battery pack with my travel Trenscend CPAP. If there is power, I use that. If no inflight power is available for use then I am still covered.

Be Prepared!

CX changed [yes, apparently flip/flops back and forth -- again] policy and now permits using on-board power. To be on the safe side, call ahead to advise them and go to their website and print out the relevant information as backup.

Using CPAP on board
 

For those with mild sleep apnea, talk to your doctor about an oral appliance. Can be an effective way to treat without CPAP, and much more portable (and comfortable).

More portable yes, more effective no. Sleep Apnea is the constant shut down of air flow, any good doctor will tell you oral appliance will only help, but not eliminate the problems of sleep apnea brings (lack of enough oxygen intake during sleep.) CPAP is the way to go if you don't want to have brain and heart damages caused by sleep apnea, even for mild.