What happened on September 17, 2026 over the Atlantic
On September 17, 2026, KLM flight KL735, a Boeing 777-300ER operated by KLM Royal Dutch Airlines, the Netherlands' flag carrier, flying from Amsterdam Schiphol to Curaçao, turned back roughly five and a half hours after take-off, while cruising over the Atlantic Ocean. The cause: a power bank that caught fire in the business class cabin, with witnesses describing a loud bang followed by visible flames.
Cabin crew reacted quickly and extinguished the fire, but the captain chose, as a precaution, to divert back to Schiphol rather than continue on to the Caribbean. The aircraft landed safely after roughly eleven hours in the air in total. Visible damage was reported to the seat, the sidewall and the window area. KLM covered overnight hotel stays for all 322 passengers in Amsterdam and arranged a replacement flight the following day.
According to the airline, no passenger sustained serious injuries. One source cited by Dutch media did report minor injuries to the power bank's own owner. KLM said it had opened an internal investigation into the exact circumstances.
Why even the airline's own former CEO broke the rule
KLM's policy is unambiguous: passengers may carry up to two power banks in the cabin, provided they stay in carry-on baggage, visible and within reach. What's explicitly banned is using or charging them during the flight, as well as storing them in the overhead bins. We already covered this rule, which took effect earlier this year, in our article on power banks on planes: you are no longer allowed to use one.
The most striking part of this incident is exactly who broke the rule: the airline's own former chief executive, arguably the person best placed to know it. This wasn't a confused first-time flyer. It was a routine, almost automatic habit, plugging in a power bank before falling asleep, just as one might at home, that was enough to trigger an emergency turnaround over the Atlantic. The lesson applies to every traveler, on any airline, US carriers included: this isn't a rule you can afford to relax on, no matter how frequently you fly.
Why you should never charge or use a power bank in flight
A lithium-ion power bank can, in rare cases, enter thermal runaway: a vicious cycle in which a damaged, poorly manufactured or overstressed cell heats up, releases energy, heats up further, and eventually ignites or explodes. This can happen without charging, but active charging raises the risk further: it stresses the cell electrically at the very moment it's also exposed to vibration, cabin pressure changes and the temperature swings typical of a flight. That combination of factors is exactly why the FAA warns that thermal runaway can occur without warning, and why in-flight charging and use are banned even though simply carrying the device is allowed.
Airlines take an in-flight lithium battery fire very seriously: cabin crews are trained to use dedicated fire-containment bags and water, never a standard dry-powder extinguisher, which is ineffective on this type of fire, to contain it until landing. The number of these incidents has been rising year over year as electronic devices multiply on board, which explains why several carriers, KLM included, have recently tightened their rules, echoing the same concerns behind the FAA's own PackSafe guidance for US flights.
Calculating your power bank's Wh before you fly: the formula to know
Beyond the in-flight usage ban, a second rule governs the transport of power banks themselves, on KLM as well as on every US carrier: a 100 Wh (watt-hour) limit per battery, generally accepted by TSA and FAA without any paperwork. Many power banks only advertise their capacity in mAh (milliamp-hours), a unit that says nothing on its own about the actual energy stored. To convert, the formula is simple:
This is far from a minor detail: makers of very large power banks (above roughly 25,000-30,000 mAh) know this well, and deliberately design their products to stay just under the 100 Wh mark, even if that means capping the advertised capacity. That's exactly the case with the Aferiy Nano100 mentioned above: its 31,000 mAh of LiFePO4 cells (which run at a lower nominal voltage than conventional lithium-ion) deliberately cap out at 99 Wh, keeping it eligible for carry-on travel without any special approval. FAA rules also allow spare batteries between 101 and 160 Wh with airline approval, and forbid anything above 160 Wh outright, a threshold that isn't set in stone forever elsewhere either: we cover the EU's planned tightening in our dedicated article, power banks on planes: anything above 100 Wh is out from 2027.
The pre-flight checklist: what's allowed, and what isn't
| Situation | Allowed? |
|---|---|
| Carrying a power bank under 100 Wh in carry-on baggage | Yes, though some airlines like KLM cap it at two |
| Packing a power bank in checked luggage | Never, per TSA and FAA rules |
| Storing a power bank in the overhead bin | Not recommended, and banned outright on KLM |
| Charging a power bank in flight | Depends on the airline; banned on KLM |
| Using a power bank to charge another device in flight | No, under KLM's rules |
| Power banks between 100 and 160 Wh | Only with prior airline approval, in limited numbers |
The core rule to remember: a power bank always travels in your carry-on, never in checked luggage, per both TSA and FAA guidance, and on carriers like KLM it must also stay switched off and out of the overhead bin for the entire flight. Looking for a compact model comfortably under the 100 Wh limit? Our power banks section lists options built for travel, from the most pocketable to the most versatile.
