A passenger noticed and recorded an issue with on wing flap of a Boeing 737-800.
After 2 hours of light, looking out the window, a passenger onboard the Air China Boeing 737-800 noticed and recorded the wing flap watching the screws slowly vibrate themselves and another one was missing.
The Air China Boeing 737-800 was performing flight #CA1921 from Beijing (PEK) to Hengyang (HNY).