Flag of the Russian Soviet Federative Socialist Republic

The penultimate USSR-era flag was adopted by the Russian Soviet Federative Socialist Republic (RSFSR) in 1954 and used until 1991. The flag of the Russian SFSR was a defacement of the flag of the USSR. The constitution stipulated: The state flag of the Russian Soviet Federative Socialist Republic (SFSR) presents itself as a red, rectangular sheet with a light-blue stripe at the pole extending all the width [read height] which constitutes one eighth length of the flag.

Source: Wikipedia — Flag of the Russian Soviet Federative Socialist Republic (CC BY-SA 4.0)