836,875. Attitude indicators for aircraft. SMITH & SONS (ENGLAND) Ltd., S. Nov. 13, 1956 [Oct. 10, 1955], No. 28812/55. Class 4. A navigational instrument for aircraft comprises a first pointer, means to move said first pointer in relation to a datum in accordance with aircraft attitude, a second pointer, and means to move said second pointer in relation to said datum in accordance with discrepancy between the actual attitude of the aircraft and a demanded attitude whereby when the second pointer is aligned with the datum the actual and demanded attitudes are equal. The instrument consists of a case and window behind which is located an index 2 representing an aircraft wherein the centre of the fuselage constitutes what is referred to as " the axis." A bank scale 3 is centred about the axis and two presettable bank limit pointers 5, 6, adjusted by a knob 7, are read against the scale 3. A carrier 24 is rotatably positioned about the axis by a servo system 25 responsive to a gyro vertical 26. This positions the carrier 24 in accordance with roll attitude of the aircraft so long as the pitch attitude is less than Π70 degrees from the horizontal and a change-over switch 27, operated by pitch output of gyro 26 when pitch attitude exceeds 70 degrees, connects servo 25 to the output of a computer 50. Carrier 24 supports a pair of rollers 28, 29, whose axes are parallel and horizontal when the aircraft is level in roll, the rollers supporting a flexible band 8 which has two distinctively coloured portions 9 and 10 separated by a line 11, referred to as the first pointer. A pitch scale is marked on the band with zenith and nadir depicted by dots 13 and 14 and a divided scale therebetween. The rollers 28, 29 are driven by a servo 30 controlled by gyro 26 and a switch 31 is operated to break the circuit when the pitch attitude exceeds 70 degrees. The carrier 24 supports for relative rotation a transparent sheet 32 located between band 8 and the window and controlled by a servo 33 in accordance with demanded angle of bank derived from a computer 34. Sheet 32 carries a bank director index, constituting a second pointer, formed by a circle 15 centred on the axis and arrows 16, 17 and a mark 18 midway between 16 and 17. When the actual and demanded bank are equal arrows 16 and 17 are aligned with " wings " of index 1 and mark 18 is directly above the " fin." Knob 7 is coupled to servo 33 to ensure that the bank demand does not exceed a maximum corresponding to the setting of pointers 5 and 6. In addition to rollers 28, 29 carrier 24 supports a further pair of rollers 35, 36 for a transparent endless band 37, part of which lying between band 8 and sheet 32 carries a pitch director index in the form of two short lines 19. The band 37 is positioned in accordance with demanded pitch attitude of the aircraft by a servo 38 such that when actual and demanded pitch attitudes are equal, lines 19 are equally spaced either side of the axis. A limit switch 40 de-energises servo 38 if the discrepancy between actual and demanded pitch exceeds 45 degrees. Thus, provided that the pitch attitude of the aircraft is within 70 degrees of the horizontal, the aircraft is controlled to align index 1 with bank director index 15, 16, 17 and pitch director index 19, when the actual attitude of the aircraft will be its demanded attitude. Bank demand may be selected by a knob 20 from a selected heading from a gyro-compass 41 or a radio beam apparatus 42. Pitch demand may be selected by a knob 21 from a selected apparatus shown as radio glide slope 47, height 46 or airspeed 45.