fall down flat

Translations
потерпеть фиаско
His plans to start a new business fell down flat.
Его планы начать новый бизнес потерпели фиаско.
Definitions
To suddenly lose one's balance and land on the ground, typically in a horizontal position; can also be used figuratively to describe a plan or idea that fails completely.
Words
fall

verb
падать
down

adverb
вниз
flat

adverb
плашмя