How to turn on Airplane Mode in the watchOS Control Center

Some airlines let you fly with your Apple Watch (and iPhone) turned on if you put them in Airplane Mode. 

By default, turning on Airplane Mode turns off Wi-Fi and cellular (on Apple Watch models with cellular) and keeps Bluetooth turned on. However, you can change which settings are turned on and off when you turn on Airplane Mode.

• Turn on Airplane Mode on Apple Watch: Press the side button to open Control Center, then tap the airplane icon.
• Put both your Apple Watch and iPhone in Airplane Mode in one step: Open the Apple Watch app on your iPhone, tap My Watch, go to General > Airplane Mode, then turn on Mirror iPhone. When your iPhone and Apple Watch are within normal Bluetooth range of each other (about 33 feet or 10 meters), any time you switch to Airplane Mode on one device, the other switches to match.
• Change which settings are turned on or off in Airplane Mode: On Apple Watch, open the Settings app , tap Airplane Mode, then choose whether to turn Wi-Fi or Bluetooth on or off by default when you turn on Airplane Mode.
  To turn Wi-Fi or Bluetooth on or off while your Apple Watch is in Airplane Mode, open the Settings app , then tap Wi-Fi or Bluetooth.

When Airplane Mode is on, the airplane icon appears at the top of the screen.

Note: Even with Mirror iPhone turned on, you must turn off Airplane Mode separately on your iPhone and Apple Watch.

(This how-to is based on my experiences and info on Apple’s support pages — where the images sometimes come from.)