A method performed by a first network node for detecting outage of a radio cell served by a second network node. The first network node and the second network node operate in a wireless communications system. The first network node determines a number of incoming handovers for the radio cell of the second network node in a first measurement period. The first network node then determines whether the radio cell is in outage, based on whether the determined number of incoming handovers in the first measurement period is under or equal to a threshold.