A gas turbine engine article comprising: an article wall defining a cavity ; and a cooling passage network embedded in the article wall between inner and outer portions of the article wall , the cooling passage network having an inlet orifice through the inner portion of the article wall to receive cooling air from the cavity , a sub-passage region including an array of pedestals , and at least one outlet orifice through the outer portion , the array of pedestals including first pedestals (83, 83.1, 83.2, 183.1, 183.2, 283.1, 283.2) arranged in a first row (85, 85.1, 85.2, 185.1, 185.2, 285.1, 285.2) and second pedestals (84, 84.1, 84.2, 184.1, 184.2, 284.1, 284.2) arranged in a second, adjacent row (86, 86.1, 86.2, 186.1, 186.2, 286.1, 286.2), characterised in that : the first pedestals (83... 283.2) and the second pedestals (84...284.2) defining inter-row sub-passages there between, each inter-row sub-passage being defined between, respectively, one of the first pedestals (83... 283.2) and one of the second pedestals (84...284.2); each of the inter-row sub-passages has an inlet mouth , an outlet mouth , and a compound channel connecting the inlet mouth and the outlet mouth , the compound channel including a first channel length over which the inter-row sub-passage has a constant cross-section and from which the outlet mouth diverges, and a second channel length over which the inter-row sub-passage has a non-constant cross-section and into which the inlet mouth converges; and the limits of the inlet mouth , the first channel length , the second channel length , and the outlet mouth are each demarcated by inflections on one or both of the sides of the respective first and second pedestals. an article wall defining a cavity ; and a cooling passage network embedded in the article wall between inner and outer portions of the article wall , the cooling passage network having an inlet orifice through the inner portion of the article wall to receive cooling air from the cavity , a sub-passage region including an array of pedestals , and at least one outlet orifice through the outer portion , the array of pedestals including first pedestals (83, 83.1, 83.2, 183.1, 183.2, 283.1, 283.2) arranged in a first row (85, 85.1, 85.2, 185.1, 185.2, 285.1, 285.2) and second pedestals (84, 84.1, 84.2, 184.1, 184.2, 284.1, 284.2) arranged in a second, adjacent row (86, 86.1, 86.2, 186.1, 186.2, 286.1, 286.2), the first pedestals (83... 283.2) and the second pedestals (84...284.2) defining inter-row sub-passages there between, each inter-row sub-passage being defined between, respectively, one of the first pedestals (83... 283.2) and one of the second pedestals (84...284.2); each of the inter-row sub-passages has an inlet mouth , an outlet mouth , and a compound channel connecting the inlet mouth and the outlet mouth , the compound channel including a first channel length over which the inter-row sub-passage has a constant cross-section and from which the outlet mouth diverges, and a second channel length over which the inter-row sub-passage has a non-constant cross-section and into which the inlet mouth converges; and the limits of the inlet mouth , the first channel length , the second channel length , and the outlet mouth are each demarcated by inflections on one or both of the sides of the respective first and second pedestals. <EOS>