Originally Posted by
lkrt
For sure there have been other booking classes than Y available.
Not necessarily, if load factor is high the lower classes may be sold out or unavailable and only Y (Pro Fare) is then available and those are notoriously expensive.
Some flights from IVL are operated as three-leg flights ie. HEL-KTT-IVL-HEL and this may affect the total load factor of a single flight.