Is it safe to charge my laptop in an airplane?

Yes, it is safe.

You obviously know that at home you get a certain voltage (e.g. 220V), and on your laptop charger it says that it accepts only that specific voltage, so when you use your laptop at home you feel safe. But in reality there is a certain level of fluctuation even at your house and unless you are using a cheap quality charger, the charger itself is designed with this in mind. Plus, no airline would go that far as to add plug to all their seats and install an additional electricity transformer, just to fry all passenger devices once in a while.

S*it can always happen, obviously, but it can happen at home exactly like it can happen in flight.

If you're really that concerned, bring along a surge suppressor and plug that into the plane's outlet then plug your laptop into that. If there's a power spike, the suppressor will eat it, if there's a dip your laptop will stop charging for a moment.

However, think about all the regulations and development time (years and billions of {insert your currency here}) that go into getting an aircraft certified for commercial service. I would venture to say that the power coming out of a socket in a plane is going to be far more clean and steady than the power coming out of a socket in your house. In no way am I minimizing the threat of a house fire, but in a house fire, a few people may be injured or killed - in a plane fire a few hundred people may be injured or killed plus anyone on the ground who happens to be in the way.

TL;DR: I believe that what you've heard about fluctuations in aircraft electrical outlets is probably incorrect. That does sound like a good question to ask at Aviation.SE.

The most popular charging system on a plane is made by Em Power. The EmPower 110VAC + USB In-Seat Power Systems (IPS) converts the three-phase 115VAC, 400Hz aircraft power into 110VAC (200 Watts maximum) and standard USB power (7.5 Amps maximum). I am unable to find specifications on the tolerances of the output and the fail safe mechanisms of the IPS.

Running a device without a battery might be problematic since any power fluctuations could cause a power cycle (i.e., a computer to reboot) which can be bad. Laptops run on DC power and the transformer (power brick) provides a fair amount of protection to moderate power fluctuations (and the battery prevents power cycling).

From experience using various devices across 100's of flights, YES, it is perfectly save to use/charge devices using on board power supplies.

What I suspect you are referring to is the occasional announcement to discontinue using the outlets at specific times. I have heard:

• Just before departure: This is because of the switch over from gate to aircraft power. It's no different from flipping a household breaker off/on which some devices are sensitive to.
• Takeoff/landing: I don't think there's anything special about this electrically (never asked). I think (again, never asked) they just don't want wires and such dangling around in case of an emergency.

Just make sure you have the right plug. Most newer aircraft are equipped with either the multi-prong 120/220V combo, USB or both depending on the carrier.

It is extremely unlikely, and even if the voltage went wonky for some reason and exceeded the limits of the 'brick' it would more than likely only damage the brick and not the computer itself.

The so-and-so in front of you in economy is more likely to suddenly recline and crush your screen or any other number of possible disasters.

If you are paranoid and are heading away from familiar places, stick a spare power brick in your checked luggage. I tend to keep spares wherever I use my notebook computer for extended periods of time. They are not unreasonable cost-wise if you order them before you need them urgently.

Edit: Power brick (huge 330W one, most are much smaller!):

If you (like me) reside primarily in a 120V country, then your poor aging power brick will suddenly see 240V for the first time in a while when you go abroad- and the chances of a sudden failure are somewhat increased, so having a spare along may not be a bad idea. Security folks can get snarky in some places if you can't demonstrate your computer starting up and force you to leave the computer behind even if you were not depending on it (I saw this happen to a fellow traveler earlier this year in Addis Ababa airport even though the connection was entirely airside).

Airplanes rely on a principle known as "Faraday Cage". Basically, if lightning hits the plane, it has no direct way to reach the ground (there is no wire connecting the plane to the ground), so the charge simply doesn't even touch the plane's electronics inside it (and in turn the sockets inside the cabin).

Same thing if you are hit by lightning while in a car (just not as efficent, since the distance between you and the ground would be way less).

You should therefore not have to worry about voltage "fluctuations" too much, and as Tor Klingberg mentioned in a comment, notebook chargers are usually designed to withstand voltage variations typically from 100-110V up to 240-250V, so you should be ok.

Another thing which no one seems to have yet discussed on this forum is the pressure factor. You may have heard about batteries exploding on planes (especially Li-ion ones). That is very rare (it never occurred to me, and I take hundreds of flight each year, always charging my laptop on board).

However, if you are really worried, you can always "limit" your max charge on the battery temporarily. Most laptops nowadays have a function called "Conservation mode" which only charges the battery up to 55-60%, which is the best range to keep it at if you want it to last you.

Hope that cleared up the situation a bit.

I don't know what could happen on a plane that is worse than the spikes and dips you get from ordinary plugging/unplugging you do every day, but if your laptop has some special value beyond its dollar cost, there seems to be one (1) company that makes USB-USB surge protectors, for less than $22.

If you are carrying a laptop around an airport and bringing it through security, your risk of losing it to thieves (including security personnel), or just forgetting it, is a hundred times higher than the risk of frying the hard-drive by plugging it into a plane, so back up your data either way.