Really Nerds Only: Final Words on AC Power on Airliners

Following previous entries here and here, on whether you could actually operate an airliner full of laptop users all plugged into 120V AC sockets -- or whether, on the contrary, the necessary power-supply gear would be so heavy that the plane would never get off the ground -- here is one last round of tech-talk reports. This is a sampling to reflect the range of views that have come in.

1) There's a lot of power available, but.... A technically-trained reader writes:

>>Thanks for honoring your nerd readers with this info.

As a PhD physicist and radio amateur, I'd chime in to say that all the difficulties with generating up to 240 Watts of AC power (120 Volts times 2 Amps) show that this is not the right solution. (For one thing, a typical laptop needs no more than 60 Watts. Your lap would suffer dreadfully if the computer was using 240W!) The laptop can't use 120V power directly; it has to be converted to about 20V DC. So direct DC distribution is the "correct" idea, bypassing your AC plug-in power supply and all the waveform issues. Some airlines have supported DC, as you mention, but we run into problems because laptops don't have standardized power connections -- requiring the airlines to sell or rent you an expensive adapter cable.

Power on an aircraft is not in short supply. One engine on a 747 is calculated to provide 87,000 horsepower or 65,000 kW at cruise (Mach 0.9 at 40,000 ft) That would keep about 3 million laptops running happily, if used for electricity. (http://www.aerospaceweb.org/question/propulsion/q0195.shtml)<<

2) Harrrummpph! Another tech veteran writes:

>>1. This is a subcase of rich people complaining about their situation.
2. You call yourself a "nerd," but you have a bare mailto href on your page. The title has to be *earned*.<<

Point 1: Yes, agreed. Point 2: Hey, it's not my "real" address!

3) It's a taste of the Smart Grid. A reader who gives his (or her) name as M. Simon, and who has developed in-airplane AC power systems, reports:

>>A certain amount of power is allocated to the AC on aircraft. It depends on the flight regime. On takeoff and landing the limits are low, in an emergency they go to zero. The design limits are based on a mix of loads and the maximum that can be allocated. And of course each outlet has a design maximum.

If the total power exceeds the maximum allowed outlets are shut down until the power demanded goes below the limit. A smart grid. In fact the ideas for the Smart Grid were developed in part by looking at how aircraft managed power demand.

If the aircraft electrical systems annoy you well - you have the Smart Grid to look forward to.

You can use my name.... And just to give your knowledgeable readers a hint. I worked for the world's premier aircraft electrical power company. Every one came to us. They still do.<<

4) Not worth the risk. An aviation veteran writes: 

>>I'm not a pilot, but I've ridden around in lots of airplanes from C140s to bizjets, mostly with over-gross collections of tech gear inside, and I hate 110VAC on an airplane. It's a safety hazard, both directly and from risk of fire, especially in a crash.

Laptop power supplies that run on "twelve volts" (i.e., an automobile's DC supply, 13.8 or 14.4 V depending on whether it's lead-acid or NiCd) for around $100. I have one from Kensington that's twelve years old and does both 85-260 50/60 Hz and 12VDC in; it works fine, takes up maybe 10-15% more volume than a "normal" one, and doesn't even get particularly warm.

12VDC to the seat would be relatively easy and cheap. Yes, I know, the airlines don't reckon they can tell their customers "sorry you have to buy something else" because they don't need to run anybody else off; TSA does fine for that. But in this case catering to their passengers is going to get somebody killed....

I'll add: the last time I flew to Europe, which was long enough ago that the majority of passengers in coach didn't have laptops, the airplane had a 12VDC outlet on every third row. I negotiated with the flight attendant to move to a row with an outlet, and had to endure the guy in the seat next to me bitch that there wasn't any 110V for him all the way to Frankfurt.

One outlet per seat in first and business, one per row in coach, would accommodate most people except commuters (DFW -- ORD, for instance). Add the outlets to the seat selection criteria. For a 767-400ER (Delta, no first class, ATL-FRA) that's 36 + 87 = 123 outlets. At 150W/outlet, just under 20KW total, 27 HP or so. The weight of the wiring would be a bigger penalty than the electricity usage, but not to the point adding inverters would be, and emergency people wouldn't have to worry about getting zapped if the thing crashed. Wire it for video at the same time, and take out the entertainment system; push and pull on weight, I bet.

For people who didn't get the hint, the airline could provide a few inverters at $25 a trip.<<

Finally, and after the jump, Authoritative Word from Virgin Atlantic itself.

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5. Virgin America speaks. Abby Lunardini, of the airline that originally touched off this discussion, writes to offer its official view:

>>Virgin America offers standard power outlets near every seat and we do have enough power to supply electricity for all outlet users onboard. We have two outlets at every three person row on our aircraft -- and the outlets were designed for full use and are certified with the FAA to do so. To obtain the FAA certification you in fact have to test multiple devices onboard at once. During this certification process, we tested the in-seat power system by operating 82 laptops, 10 DVD players and 10 electrical load devices simultaneously (it should be noted, we would almost never see this kind of use on a real flight). Each pair of outlets at every row of three can support a maximum total of 225 watts per this certification, but there is "enough power" onboard for every outlet on average to deliver 82 watts to every outlet in the aircraft at any given time.

The issue we believe Mr. Rosen unfortunately encountered relates to usage/surge protection and can affect some laptop users, (per what the second post notes. Newer laptops and certain types of AC charger/adaptors in particular have been more closely linked to this occurrence. Seat guru, an airline blog has a good overview of this too here. Unfortunately some computer power supplies may present a request for power with a momentary amperage spike that is interpreted by the in-seat power system as a surge. That said, in these limited instances, 80% of the time - plugging and unplugging the device will rectify the temporary surge protection, but occasionally, and in this case, it does not address the issue. We are sorry Mr. Rosen had this experience, and as mentioned, our engineering team has been working on how to address this issue for some users. They are also evaluating new in-seat power supply surge protection to help eliminate this limited issue on our new aircraft. Most people do not have an issue with the power, and it is in fact one of our most complimented features. I believe we are still the only domestic airline to offer standard outlets in every class of service on every flight.<<

That is all.