A mysterious smell wafting through a United Airlines cabin led to a frightening flight diversion to a small island in the Pacific Ocean Friday.
The flight, headed to Guam from Honolulu, landed on remote Midway Island, stranding 335 passengers and 13 crew members for over seven hours.
Some passengers likened the smell to smoke or something burning, while United Airlines spokespeople and FAA officials called it an "electrical smell."
That abnormal electrical smell - what is it?
"It's actually ozone," Soucie said.
Ozone is three molecules of oxygen - O3 - rather than O2, which comprises water or moisture, according to Soucie.
How is ozone produced?
Soucie said that ozone is caused by arcing, which is the flow of electrical current in the air, from one conductor to another.
A lightning strike, Soucie explained, would also create ozone.
"This fan that failed has brushes in it that make a motor," Soucie said, referring to the plane's equipment cooling fan.
An internal short in the fan could create sparks, which, in turn, would create the smell of ozone.
Is ozone dangerous?
"Extended exposure can be harmful to your lungs, your mouth," Soucie explained.
"It can make you very irritated."
In a statement, United Airlines said the mechanical issue was due to a problem with an equipment supply cooling fan, which they say has been corrected.
The aircraft was put back in service on Saturday.