An angle of attack sensor comprising: a vane assembly ; a multi-piece faceplate adjacent the vane assembly , the faceplate including: a mounting plate having an opening and an exterior surface ; a chassis , the chassis being positioned adjacent the mounting plate and having a ring portion extending through the opening , the ring portion defining a ring-shaped deflector that surrounds the vane assembly and extends above the exterior surface of the mounting plate , wherein the deflector includes: a fore ramp at an upstream portion of the deflector; and an aft ramp at a downstream portion of the deflector, wherein the fore ramp including an inclined outer surface extending with an incline in an aft direction to a height above the exterior surface of the mounting plate ; characterised by : the aft ramp including an inclined inner surface extending with an incline in the aft direction to a height above the exterior surface of the mounting plate ; and wherein the chassis is a heated chassis with a heater positioned on, or embedded in, the heated chassis . a vane assembly ; a multi-piece faceplate adjacent the vane assembly , the faceplate including: a mounting plate having an opening and an exterior surface ; a chassis , the chassis being positioned adjacent the mounting plate and having a ring portion extending through the opening , the ring portion defining a ring-shaped deflector that surrounds the vane assembly and extends above the exterior surface of the mounting plate , wherein the deflector includes: a fore ramp at an upstream portion of the deflector; and an aft ramp at a downstream portion of the deflector, wherein the fore ramp including an inclined outer surface extending with an incline in an aft direction to a height above the exterior surface of the mounting plate ; characterised by : the aft ramp including an inclined inner surface extending with an incline in the aft direction to a height above the exterior surface of the mounting plate ; and wherein the chassis is a heated chassis with a heater positioned on, or embedded in, the heated chassis . a mounting plate having an opening and an exterior surface ; a chassis , the chassis being positioned adjacent the mounting plate and having a ring portion extending through the opening , the ring portion defining a ring-shaped deflector that surrounds the vane assembly and extends above the exterior surface of the mounting plate , wherein the deflector includes: a fore ramp at an upstream portion of the deflector; and an aft ramp at a downstream portion of the deflector, a fore ramp at an upstream portion of the deflector; and an aft ramp at a downstream portion of the deflector, wherein the fore ramp including an inclined outer surface extending with an incline in an aft direction to a height above the exterior surface of the mounting plate ; characterised by : the aft ramp including an inclined inner surface extending with an incline in the aft direction to a height above the exterior surface of the mounting plate ; and wherein the chassis is a heated chassis with a heater positioned on, or embedded in, the heated chassis . the aft ramp including an inclined inner surface extending with an incline in the aft direction to a height above the exterior surface of the mounting plate ; and wherein the chassis is a heated chassis with a heater positioned on, or embedded in, the heated chassis . <EOS>