An interferometer comprising a base (12) forming an interior (86), and first and second optical members (14 and 16) located in the interior of the base. The interferometer further comprises a first retainer assembly (20) connecting the first optical member to the base, translation means (24) for moving the second optical member (16) relative the first optical member (14), to vary the distance between the first and second optical members, and a second retainer assembly (22) connecting the second optical member to the translation means (24). The preferred mechanical configuration and design features of the interferometer produce a very durable instrument that can rapidly scan and accurately filter light across a wide bandwidth. This uniquely designed instrument combines high speed switching, high resolution, wide bandwidth, and adjustable damping capabilities in a durable flight capable instrument.

@ A colour cathode ray tube (54) has raster scan colour zones defined by X and Y positional signals derived from a stroke vector generator (51) and stored in a digital memory. Raster scan and stroke vector displays are alternately presented in a hybrid display. The display face (10) of the tube is scanned by a plurality of raster lines and a colour transition point is defined by the intersection of a stroke vector with a raster line. The X and Y addresses of the intersection points define the raster line, pixel element, and colour at the transition point. The system is arranged so that the X and Y addresses are provided by the stroke vector generator (51) in synchronous relation with the colour transition points, and read into memory during the stroke vector refresh period. During the raster scan refresh period, the memory contents are recalled in synchronism with the raster scan, passed through a digital-to-analogue converter, and then applied to the display tube to provide filled- in colour zones superposed on the stroke vector display. The reduced memory requirements and controller access time permit dynamically rotating symbology in a synthetic display for aircraft flight instrumentation.

An airplane precision approach guidance system and method. The airplane precision approach guidance system includes: (i) GPS landing system (GLS) components (12) for receiving and processing signals from GPS satellites (30) and a GPS ground station (32) and generating a first set of velocities; (ii) an inertial reference system (IRS)(20) for generating a second set of velocities; and (iii) guidance software (24) for generating a cross-runway velocity and a lateral distance from runway centerline based on received runway centerline information and the generated first and second set of velocities. The airplane precision approach guidance system also includes flight instruments (26) and an autopilot system (28) for receiving and processing the information produced by the guidance software. The guidance software may be executed by a conventional airplane processor, such as the GLS processor, the IRS processor or the airplane's autopilot processor, or by a separate stand-alone processor. The runway centerline information may be stored at the ground station or in local memory. The ground station can also provide differential GPS information. In airplanes that include redundant systems, voting is used to determine which IRS supplies the second set of velocities.