Por que o Samsung Galaxy Note7 é proibido em voo?

In the US, as of 16 September, from the Federal Aviation Administration:

Following a Consumer Product Safety Commission recall of the Samsung Galaxy Note 7, the FAA is issuing general guidance to airlines about the rules for carrying recalled or defective lithium devices on board aircraft as cargo or in carry-on luggage.

And Samsung's recall of the product updated 20 September 2016, following reports of a flaw in the batteries which causes them to catch fire and explode.

Samsung Galaxy Note7 Battery Safety Recall and Exchange Program

Samsung has announced a voluntary recall and exchange program on certain Galaxy Note7 devices in cooperation with the U.S. Consumer Product Safety Commission (CPSC). The affected devices were sold in the U.S. before September 15, 2016. Since the affected devices can overheat and pose a safety risk, if you own a Galaxy Note7, it is extremely important to stop using your device, power it down and immediately exchange it using our U.S. Note7 Exchange Program.

In addition to the United States, aviation authorities in a number of other countries are banning the use, and currently include Australia, Singapore, the United Arab Emirates, Pakistan, the Philippines, and India.

Update: 6 October 2016

And it continues to get worse: according to this 6 October 2016 article by Zach Epstein, entitled Under no circumstances should you buy a Galaxy Note 7

Then, the unthinkable happened: a “safe” Galaxy Note 7 that had been issued to a customer as a replacement phone exploded and caught fire. On an airplane.

The plane was evacuated and no passengers were harmed by the incident, but this is, as they say, the straw that broke the camel’s back. Samsung has yet to confirm or deny anything since it must first retrieve the phone and launch an investigation, but The Verge was in contact with the phone’s owner, who provided extensive evidence to prove that the phone was in fact a newer replacement model. He gave the blog a photo of the Note 7’s box, which indicated that it was indeed a replacement phone. He also supplied his IMEI number, which was checked using Samsung’s online tool and found to be a “safe” device.

Update 2: Done and dusted: Reuters 11 October 2016

Samsung Electronics Co Ltd (005930.KS) scrapped its flagship Galaxy Note 7 smartphone on Tuesday less than two months after its launch, dealing a huge blow to its reputation and outlook after failing to resolve safety concerns.

Samsung announced the recall of 2.5 million Note 7s in early September following numerous reports of the phones catching fire and on Tuesday it finally pulled the plug on the $882 device in what could be one of the costliest product safety failures in tech history.

"(We) have decided to halt production and sales of the Galaxy Note 7 in order to consider our consumers' safety first and foremost," the South Korean firm said in a filing to the Seoul stock exchange."

Samsung just issued a worldwide recall of all versions of its Galaxy Note 7 smartphone — only it never used the word recall. The company has asked all its partners to immediately halt sales of all versions of the phone, original and replacement, and advises all owners to immediately power down their devices.

Update 3: Beating the Dead Horse

DOT Bans All Samsung Galaxy Note7 Phones from Airplanes

WASHINGTON – The U.S. Department of Transportation (DOT), with the Federal Aviation Administration (FAA) and the Pipeline and Hazardous Materials Safety Administration (PHMSA), today announced it is issuing an emergency order to ban all Samsung Galaxy Note7 smartphone devices from air transportation in the United States. Individuals who own or possess a Samsung Galaxy Note7 device may not transport the device on their person, in carry-on baggage, or in checked baggage on flights to, from, or within the United States. This prohibition includes all Samsung Galaxy Note7 devices. The phones also cannot be shipped as air cargo. The ban will be effective on Saturday, October 15, 2016, at noon ET.

What air travelers should know

• If passengers attempt to travel by air with their Samsung Galaxy Note7 devices, they will be denied boarding.

• Passengers who attempt to evade the ban by packing their phone in checked luggage are increasing the risk of a catastrophic incident. Anyone violating the ban may be subject to criminal prosecution in addition to fines.

• Passengers currently traveling with Samsung Galaxy Note7 phones should contact Samsung or their wireless carrier immediately to obtain information about how to return their phones and arrange for a refund or a replacement phone. Samsung has provided guidance for customers about refund and replacement options, as well as how to contact wireless carriers, at Samsung. Samsung is also answering customers’ questions at 1-844-365-6197.

• If an airline representative observes that a passenger is in possession of a Samsung Note7 device prior to boarding an aircraft, the air carrier must deny boarding to the passenger unless and until the passenger divests themselves and their carry-on and checked baggage of the Samsung Galaxy Note7 device. Passengers absolutely should not pack the phones in their checked luggage.

• If a flight crew member identifies that a passenger is in possession of a Samsung Galaxy Note7 device while the aircraft is in flight, the crew member must instruct the passenger to power off the device, not use or charge the device while aboard the aircraft, protect the device from accidental activation, including disabling any features that may turn on the device, such as alarm clocks, and keep the device on their person and not in the overhead compartment, seat back pocket, nor in any carry-on baggage, for the duration of the flight.

Essa modelo is prone to spontaneous battery combustion, not desirable inflight.

A specific example of this is shown here: Plane crew douse smoking Samsung phone

Given that the Note 7 has a product recall in progress due to exploding batteries, I would suggest not carrying it at all until it has been replaced.

And the airlines have no interest in trying to find every Note 7 and check its serial number to see if it is one of those considered dangerous or not. It's easier to make a blanket rule for now. I really can't blame them.

Public perception of a potential hazard warrants a company in charge of delivering thousands of people per hour to take steps to prevent anything from happening that could negatively impact passenger safety and the corporate bottom line.

Specifically if any product gets known for spontaneous combustion it will obviously be banned from any major mode of mass transit.

A resposta simples

It's hysteria and plain stupidity, not based on any objective facts, but you cannot do anything against it. The airline follows a recommendation by the FAA, and whatever the FAA says is pretty much "The One And Only Truth" (well, not exactly, but... it's what applies, anyway).

They tell you "phone off", and you had better comply, or it may get muito expensive and uncomfortable for you.

It is highly likely that other airlines (with few, if any exceptions) will follow this example, if for no other reason than because they want to eliminate every possibility of a liability.

A more elaborate answer

All batteries (or more general, all energy carriers, and energy converters) are dangerous. This is a necessary consequence from storing and converting energy.

Batteries, and in particular lithium ion batteries (which can store a lot of energy compared to their weight) have gained particular media attendance ever since becoming mainstream. Used to be cell phones were banned from gas stations because of the risk of explosions. I'm not aware of a single case where conclusive, unalleged evidence was presented that a cell phone caused a fire at a gas station.

For fairness, it should also be noted that battery fires (not just in phones, but also e.g. electric cars) generally do not occur during normal operation when a device is turned on. In theory, this is of course possible, however, it just isn't what happens in practice.
Catastrophic things happen, if they happen, when the battery is being charged (especially turbo-charged, or turbo-over-charged), or when you do things that you really shouldn't be doing to a battery, such as crashing a car into it at 180km/h (happened in China last year), pouring gasoline over it and lighting it, driving a nail right through the battery, or deliberately provoking a short circuit with a piece of wire. Or, other things that are outright nuts.

The detail about charging is the only one that can razoavelmente happen in normal operation if you are unlucky to have a somewhat crappy battery (thanks to everything having to be super cheap nowadays). But even so, it is not much a surprise. Indeed, it is a perfectly normal thing for a battery to considerably heat up during charging, especially towards the end of the charge cycle. Only just... it preferrably shouldn't catch fire!
What's to be learned from this? Well, don't charge your phone over night, and don't hit it with a hammer, and you will be good until you get a replacement. The idea of preventing incidents by not turning on devices is... funny. But, unluckily, in this case it's not reason that counts, but what you're being told.

That aside, there is an accepted standard for representing defects of any kind in the industry (... any defect, any kind of industry), the famous six-sigma, or 3.4 DPMO ("defects per million opportunities") figure. Note that a "defect" can be anything from a customer being unhappy with phone support being unresponsive, or simply one guy in the company not getting his report in time, to a piece of clothes having a bad suture, or, well... an airplane exploding mid-air. There exists an entire specialist industry around applying this principle.

It is universally accepted that reaching "six sigma" is the holy grail. In practice, few not-life-threatening products or services even come close (most are more like 3-4 sigma). The reason is simple: It is exceedingly difficult and expensive to have such a low defect rate.

It so happens, however, that 3.4 DPMO (6σ) is universally considered the gold standard for battery segurança. Which means you must meet this target to avoid people pointing fingers at you.

Now... the particular model manufactured by Samsung had 35 defects with catastrophic failure in 2 million units sold. That is 17.5 DPMO, or 5.7 sigma. Not bad, but clearly, Samsung has failed to meet the standard. But what does it really mean? Are all Samsung phone owners going to die in a fiery inferno?

Tesla had 2 battery-fire incidents (that made it to public!) among 100,000 units of Model S produced. That's 20 DPMO, worse than Samsung's. Did the Department of Transports ban Tesla cars from the streets?

Boeing, a leading airplane manufacturer, had 4 confirmed lithium-ion battery fires (that made it to public!) among 455 produced units of its 787 model. That's 8,790 DPMO, and you would be inclined to think that an airplane is a somewhat more "mission critical" thing than a cellphone. Should we ban Boeing airplanes?

Nokia and Sony had similar events like Samsung in 2004 and 2006, but on a much larger scale (Sony was around 10 million units, and that was when the mobile device market was about 1/5 of what it is now!). Only just they didn't make a big fuss about it like Samsung did. BYD had several incidents that were played down. In some, people burned in their cars. Fujitsu, Sharp, and IBM, they all had at least one fire-hazard battery recall in the 6-digit scale during the last 10 years. At the present time, HP is running a battery recall/replacement program due to fire hazard for the ProBook and Envy, Presario, and Pavillon lines sold between 2013 and 2015. Only just, it's not big news all over the media.

You have your company's server in a datacenter that guarantees 99.9% uptime? Well, congrats, that is 1,000 DPMO. If you can guarantee zero failures that are within your responsibility, your business still only operates at a sigma level of 4.5.

With these numbers in mind, I think Samsung did a good, responsible move at risk mitigation (in face of a not truly critical failure rate), but a truly terrible job at Marketing.

The result is, well, the hysteria that you see.

(No, I don't work for Samsung, and I don't own Samsung stocks. I don't have a Samsung phone either.)

The reason is not simply that the devices may catch fire, it's also because terrorists could then exploit any such design flaws that makes such devices prone to catching fire or exploding. All you need let a plane crash is to start a fire that cannot easily be put out, alkali metals are ideal for this purpose. We must keep this in mind when considering the arguments in Damon's (otherwise excellent) answer.