A gas turbine engine comprising: an outer case structure having a radially extending mounting portion, an axially extending longitudinal portion and a forward edge; and an intake duct, wherein the outer case structure is coupled to the intake duct by a compression interface formed by a K-seal and a non-metallic engine case inlet compression seal (70; 70A), the non-metallic engine case inlet compression seal (70; 70A) comprising: an arcuate interface section (72; 72A) and a longitudinal leg section that extends from said arcuate interface section (72; 72A) and axially along the direction of the central longitudinal engine axis; and characterised in that: the non-metallic engine case inlet compression seal (70; 70A) is a circular J-seal which further comprises a non-metallic mount flange section that extends radially from said longitudinal leg section and is mounted to the forward circumferential side of the mounting portion of the outer case structure; the leg section is supported on the longitudinal portion of the outer case structure and includes a stepped surface that abuts the forward edge of the outer case structure; and in that the arcuate interface section (72; 72A) and leg section are non-metallic. an outer case structure having a radially extending mounting portion, an axially extending longitudinal portion and a forward edge; and an intake duct, wherein the outer case structure is coupled to the intake duct by a compression interface formed by a K-seal and a non-metallic engine case inlet compression seal (70; 70A), the non-metallic engine case inlet compression seal (70; 70A) comprising: an arcuate interface section (72; 72A) and a longitudinal leg section that extends from said arcuate interface section (72; 72A) and axially along the direction of the central longitudinal engine axis; and characterised in that: the non-metallic engine case inlet compression seal (70; 70A) is a circular J-seal which further comprises a non-metallic mount flange section that extends radially from said longitudinal leg section and is mounted to the forward circumferential side of the mounting portion of the outer case structure; the leg section is supported on the longitudinal portion of the outer case structure and includes a stepped surface that abuts the forward edge of the outer case structure; and in that the arcuate interface section (72; 72A) and leg section are non-metallic. an arcuate interface section (72; 72A) and a longitudinal leg section that extends from said arcuate interface section (72; 72A) and axially along the direction of the central longitudinal engine axis; and characterised in that: the non-metallic engine case inlet compression seal (70; 70A) is a circular J-seal which further comprises a non-metallic mount flange section that extends radially from said longitudinal leg section and is mounted to the forward circumferential side of the mounting portion of the outer case structure; the leg section is supported on the longitudinal portion of the outer case structure and includes a stepped surface that abuts the forward edge of the outer case structure; and in that the arcuate interface section (72; 72A) and leg section are non-metallic.