Stores Ref. No.:6TD/898, and later 6TD/4550162
Connection:Mc.Murdo red range


The speed display, otherwise known as the A.S.I. - Air Speed Indicator (and colloquially as the 'strip speed indicator') presents the indicated air speed in knots and mach. It also has a power indicator (orange disk).

When Data Link was fitted to the aircraft, the system could control a 'command' speed indication, by means of an additional display tape showing a circle, plus a counter fitted in the lower port corner. This facility has been removed from this indicator, the (circle) tape and counter are missing.

The display unit can be split into three main modules:

Electronics module

The electronics module contains various transformers, early transistors, relays capacitors and resistors.

Navigation display Mk. 1 type C internals

Drive module

The drive module contsists of three servomotors to drive the display tapes, and synchro control transformers for tape position feedback. The motors and synchros interface to the electronics module by a single D type connector.

Navigation display Mk. 1 type C internals

Display module

The display module houses the rollers for the moving tapes, and interfaces with the drive module by bevel gears.


To control the motors and read sycnhro position feedback, I intend to build a modern replacement for the electronics module. this removes ths issues of: a) having no circuit diagrams or information on this module, b) reliance on ageing capacitors. This approach also means I can use standard circuits also employed to interface with other motors and synchros.


F Mk. 3, T Mk. 5 and F Mk. 6 aircrew manual:
A.P.101B-1003, 5 & 6A, Part 1, Chapter 7, A.L.2, Nov 1984 - Instruments - Paragraph 35

T Mk.5 electrical "Vol. 1":
A.P.101B-1005-1B, Sect. 7, Chap. 3B, A.L.67 Nov 1975, Air Data System - Paragraph 10
A.P.101B-1005-1B, Sect. 7, Chap. 3C, A.L.67, May 1975 - Dynamic Flight Reference System - Paragraph 5