Dehydrated?
 

Have travelled as a pax recently on the 787 and the 777, and although the flight on the 787 was nearly 2x as long as the flight on the 777, i arrived feeling significantly less dehydrated/groggy/horrible than i did when i stepped off the 777. I understand the air is from a different source (not bleed air off the engine for the 787?). Is that correct?

A few questions:

1. Do flight crew on the 777 just feel awful after every flight vs. those flying the 787?

2. How does the 787 compare to Airbus widebody aircraft? specifically the 350 or 380?

3. Would this ever become a factor in one's choice of fleet? I certainly don't feel I could commit to a career on the 777 the way I felt after that flight, but the 787 was a totally different story.

Cheers

The 777 does suck the life out of you. Still, as long as the electronics and mechanicals are taken care of, no need to worry about the human machine is there?

1. Hydrate, hydrate, hydrate. Bring the 1.5L big boy bottles to the flight deck.

2. No idea

3. Not for me personally but I do know a pilot who switched from 75/76 to the 78 for physiological reasons ( I guess).

The 787 is pressurized to a lower pressure altitude (i.e. higher cabin pressure) than the 777 - IIRC 777 cabin altitude maxes out at 8k, while the 787 maxes out at 6k.
While you are correct that the 787 doesn't use engine bleed air, if the engines are healthy (i.e. not introducing contamination into the bleed air) there is no real difference in air quality.
I've not flown a 787 (that'll change this summer), but the higher pressurized cabin is less 'draining' (especially if you live near sea level), and will be a bit more humid. The air on any pressurized aircraft tends to be very dry because the incoming (very cold) air is very dry - it's important to stay hydrated on long flights.
There is an option on the 787 to have humidifier to raise the cabin humidity but I don't know if anyone actually uses it.
BTW, my understanding is that the 777X incorporates the higher cabin air pressures similar to the 787, although it still uses engine bleed air to pressurize the cabin.

Having flown a lot on both types, it’s a bit more nuanced. Yes, the 787 has a lower max cabin alt but as the 777, especially the -300, often cruises significantly lower it can have a similar cabin alt for much of the journey. As TD says, it’s the same air coming in and being compressed so where’s the difference? No-one uses humidifiers AFAIK as it’s a cost option, both initially and in running. Our 787s have the CAC output set to max, irrespective of the number of pax, as they’ve found they break much more often at reduced flow rates. A lot of people say they feel better on the 787 but is that because they’ve been told they should?

As far as hydration goes, the amount you lose in an ultra-low humidity environment is not that much more than normal but you feel much dryer. Desert climates can have very low humidity levels but unless you’re running around like a mad thing, you don’t actually need that much more fluid input. That said, if you feel thirsty you are in the first stages of dehydration, so little and often. We have had passengers with water poisoning after drinking too much having read on the Internet somewhere that you had to chuck down at least a litre an hour on a flight because of the dry air...

I've often wondered about this. I would like to see an study on the topic.

Under equal coffee/alcohol intake conditions?

I was once told by a colleague to try and drink ~500ml of water an hour when flying. To be honest this is perhaps a bit overkill but I try to keep to it, and it makes a huge difference to my fatigue resistance/tiredness levels. That might of course be because I need the loo more often!

I’ve never felt as dehydrated as when traveling in a 777 although I like the aircraft, the 747 was much better, I have found the 787 to be pretty good

This bear of little brain does not understand. Surely if the 777 has a max cabin alt of 8,000 ft, and the 787 has a max cabin alt of 6,000 ft, even if the 777 "cruises significantly lower", cruise alt will be significantly higher than 8,000 ft, so that the cabin pressure will be 8,000, vs the 787 at 6,000. What have I missed? :confused:

The "8000 feet cabin altitude" figure is a maximum number on most planes, if they're cruising below the max altitude then your actual cabin altitude can and will be lower than 8000 feet. It’s dependent on max PSID (differential pressure between outside and inside). So the lower you fly, the lower the cabin can be.

The bit you’ve missed is that the cabin altitude will not rise to 8000ft if you’re cruising low. Most aircraft try to pressurise the cabin close to the max allowed pressure differential (delta p) to keep the cabin altitude as low as possible. If a 777 starts cruising at say FL320, you may find the initial cabin altitude is about 7000ft. I’m plucking the numbers out of thin air (no pun intended) but hopefully that gives you some idea.

Thanks. I'd assumed that as it went up past 8,000, the internal level would go to, and stay at, 8,000.

The point is, the max cabin delta P on the 787 is higher than the 777. So, if champair suggests they pressurize to the max delta P, at say 32k, the 787 will still have a lower cabin pressure altitude (high cabin pressure) than a 777 (or most aircraft for that matter, since 8k has long been something of an industry standard). Hence the comment 'max out at 8k for the 777 vs. 6k for the 787 (again, those numbers are from memory and 787 might be a bit off).
Most people will find that a lower cabin pressure altitude leaves them less drained, as there is more breathable air (and hence more O2).

Having been lucky enough to fly long range on the 777, 747, A346, A332, A388, 787 and A359, I can confirm that flights on the last two types were much much comfortable than on the first five types.
I do remember when getting out of the A/C after our first flight on an A359 (MUC to YVR - 10 hours), both my wife and I said at the same time "it's quite surprising;: I am not tired as usual !".
No miracle on that: tdtracer is fully right in mentioning the 8000 feet (777, 747, A346, A332, A388) vs the 6000 feet (787, A359) cabin altitude as the main reason for the feeling of comfort.
When possible (and ticket price permitting of course), I now privilege 787 and A359 when booking long range flights.

Yes. The normal operating differential is 8.6psi which at FL320 would give a cabin alt ~4,000’. I think the 787 is 9.4psi, which would give the same cabin alt of ~4,000 at FL360/370. From my observations, that’s about what you see in terms of initial cruise levels for a long-range flight in the 777-300 and 787.

If the aircraft are at the same level, then the 787 is going to have a lower cabin alt, up to 2,000 less, depending.