A nacelle inlet structure of an engine assembly, the nacelle inlet structure comprising: an inlet inner barrel extending circumferentially around an engine axis of the engine assembly and extending at least partially along a direction parallel to the engine axis; and an inlet outer barrel at least substantially enclosing the inlet inner barrel and extending circumferentially around the engine axis and at least partially along a direction parallel to the engine axis; wherein the inlet inner barrel includes: a tubular portion that extends at least partially along a direction parallel to the engine axis; an inlet attachment flange extending from the tubular portion and configured to be operatively coupled to an engine case of the engine assembly to operatively couple the nacelle inlet structure to the engine case, wherein the inlet attachment flange is integrally formed with at least a portion of the tubular portion, and further wherein: the inlet inner barrel includes a flange transition region extending between and interconnecting the tubular portion and the inlet attachment flange; wherein the flange transition region is integrally formed with the inlet attachment flange and at least a portion of the tubular portion; and wherein the flange transition region is curved between the tubular portion and the inlet attachment flange; the inlet inner barrel includes an inlet radius channel defined between the flange transition region and the tubular portion; and wherein the inlet inner barrel further includes an inlet radius filler that at least substantially fills the inlet radius channel, said inlet radius filler being configured to enhance a rigidity of the inlet attachment flange relative to the tubular portion. an inlet inner barrel extending circumferentially around an engine axis of the engine assembly and extending at least partially along a direction parallel to the engine axis; and an inlet outer barrel at least substantially enclosing the inlet inner barrel and extending circumferentially around the engine axis and at least partially along a direction parallel to the engine axis; wherein the inlet inner barrel includes: a tubular portion that extends at least partially along a direction parallel to the engine axis; an inlet attachment flange extending from the tubular portion and configured to be operatively coupled to an engine case of the engine assembly to operatively couple the nacelle inlet structure to the engine case, a tubular portion that extends at least partially along a direction parallel to the engine axis; an inlet attachment flange extending from the tubular portion and configured to be operatively coupled to an engine case of the engine assembly to operatively couple the nacelle inlet structure to the engine case, wherein the inlet attachment flange is integrally formed with at least a portion of the tubular portion, and further wherein: the inlet inner barrel includes a flange transition region extending between and interconnecting the tubular portion and the inlet attachment flange; wherein the flange transition region is integrally formed with the inlet attachment flange and at least a portion of the tubular portion; and wherein the flange transition region is curved between the tubular portion and the inlet attachment flange; the inlet inner barrel includes an inlet radius channel defined between the flange transition region and the tubular portion; and wherein the inlet inner barrel further includes an inlet radius filler that at least substantially fills the inlet radius channel, said inlet radius filler being configured to enhance a rigidity of the inlet attachment flange relative to the tubular portion. the inlet inner barrel includes a flange transition region extending between and interconnecting the tubular portion and the inlet attachment flange; wherein the flange transition region is integrally formed with the inlet attachment flange and at least a portion of the tubular portion; and wherein the flange transition region is curved between the tubular portion and the inlet attachment flange; the inlet inner barrel includes an inlet radius channel defined between the flange transition region and the tubular portion; and wherein the inlet inner barrel further includes an inlet radius filler that at least substantially fills the inlet radius channel, said inlet radius filler being configured to enhance a rigidity of the inlet attachment flange relative to the tubular portion.