When hurtling through the air in a metallic cylinder at 600 mph, it's nice to know that the strange things you hear and see don't mean you're going to die. Here's what not to worry about.
Flickering lights
Most airlines plug into the airport’s electricity source when planes are on the ground. When an airplane pushes away from the gate, the pilot will switch from the ground power source to the one on board, which will cause the lights in the cabin to momentarily flicker.
Two thumps and a high-pitched whir right after takeoff
When the plane lifts off the ground, the pilot pulls the wheels into the plane’s body and closes the flaps behind them, one at a time (thump, thump). That disconcerting whir comes from the pilot retracting the wing flaps that were needed to get the plane off the ground. Both of those actions are part of the process of “cleaning up the plane” to make it streamlined for flight.
White "smoke" in the cabin
What you’re seeing streaming from the air vents is the water vapor (similar to fog) that appears when warm and cool air mix. Most commonly, the white vapor will appear in hot and humid conditions, either with the plane on the ground with its doors open or when an airplane flies through a storm.
One, two, or three (or more) chimes
Each airline uses chimes differently, according to John Cox, a retired airline captain. One chime can be the pilot warning flight attendants of turbulence or the flight attendants asking if the pilot wants a cup of coffee. Two chimes usually means that the airplane is approaching 10,000 feet. Three or more chimes indicates a more serious issue, such as a very sick passenger to impending extremely rough air.
"Doors to arrival and cross-check"
When an airplane’s doors are closed, an escape slide is automatically enabled. “Doors to arrival” reminds flight attendants to disarm the slide, and “cross check” is a directive to double check the door of another flight attendant.
"All call"
This announcement is a request for a sort of conference call for the crew. Each flight attendant calls in to report that he or she has completed the assigned safety checks.