Flann dá Chongal (d. 740?), son of Díummasach and king of Uí Fhailge, features prominently in the genealogies of Uí Fhailge, where he is represented as the common ancestor of a number of lineages including Clann Cholccan, Clann Chináeda, Clann Máel-ugrai, Clann Chairpri, and Uí Riacáin. Flann aue Congaile (grandson of Congal), although not featured in the regnal poem on Rathangan, is included in the Uí Fhailge king-list, where he is apparently to some degree misplaced (LL, 40c). He was probably a successor, rather than a predecessor, of Forbasach grandson of Congal (a cousin, it seems) who in 714 was defeated and slain at ‘Garbshalach’ in the Westmeath lakelands by the king of Uisnech, Murchad Midi (qv).
Flann's principal wife was Érennach, a daughter of Murchad Midi; in the light of such a marriage-alliance it may be reasonable to view the rise of the Uí Fhailge king as part of a quid pro quo whereby he abandoned his dynasty's claims to the lakelands in favour of Clann Cholmáin. Flann is credited with a total of thirteen sons: Érennach was the mother of four whose names are given as Cummascach, Cináed, Mugrón, and Flaithbertach. He had another four by a daughter of one Flann Léna: Tomaltach, Indrechtach, Írgalach and Cathussach. There is no record of the mother(s) of Ailill Corrach, Flathnia, Óengus, Cairpre, or Cellach.
As the Uí Dúnlainge dynasty of north Leinster under Fáelán (qv) son of Murchad (qv) was clearly struggling to maintain its claim to overkingship of the province, Flann dá Chongal appears to have thrown his weight behind the Uí Chennselaig claimant, Áed Menn (qv) son of Colcu. When the latter was slain by the Uí Néill at the disastrous battle of Áth Senaig (possibly Ballyshannon near Kilcullen, Co. Kildare; 19 August 738), four of Flann's sons fell in the engagement. It may be taken that Flann himself died in 740; the alternative date of 751 supplied by AU seems too late. Five of his sons succeeded to the kingship of Uí Fhailge: Ailill Corrach, who appears to have had a brief reign; Flathnia (d. 755); Cummascach; Cináed (d. 770); and Mugrón (d. 782).