Their ears hurt
Many babies experience pain in their ears when flying due to the pressure, which could make them cry.
They’re sitting in an uncomfortable position
If a baby is being carried in one position by their mother the whole flight, they might start feeling uncomfortable, which may lead to crying.
The air smells strange
Babies might start crying on planes when the air smells strange to them, as babies are affected by the slightest change in their environment.
The noises are too loud
Babies on airplanes could start crying due to the loud noises of the plane that irritate them.
Due to turbulence
When a plane goes through rough turbulence it might get scary for all passengers, including babies who might start crying. (See Why am I afraid of flying?)
They have an upset stomach
Babies on a plane might start crying if they’re experiencing an upset stomach.
It’s been a long trip
Long trips can get exhausting for most flight passengers, and babies might start crying when they’re feeling tired as well.
They don’t like wearing seat-belts
Older kids who get to sit in a seat of their own might start fidgeting and crying when they’re forced to wear their seat belt.
Children on planes might start crying when they feel bored on a long flight and not having anything to do.
They’re not getting their sleep
Babies might start crying during a flight if it’s scheduled during their sleep time, which could make them cranky and fussy. (See How to Have a Good Night Sleep?)
They’re used to a certain environment
Babies could start crying on planes because they experience a change in the environment they’re used to.
Babies might simply start crying on planes when they feel hungry. Crying in this case is a signal that they want to be fed.
What to Expect Being on a Plane for the First Time? What does it feel like to fly a plane for the first time?