RAF issue Aircraft Clock, 6A/5183
Introduction
1. The time of flight clock (Ref. No. 6A/5183) provides a very accurate time datum for the purpose of astro-navigation and when required, records the time taken to complete a flight.
2. The time of flight clock is complementary to the elapsed time clock (Ref. No. 6A/5184). The two clocks constitute a set.
DESCRIPTION
3. The clock is of the 8-day type, having a movement incorporating 23 jewels and a Breguet overcoil hairspring.
4. The time of day is shown on a conventional 12 hour dial for which a sweep centre second hand is provided.
5. A subsidiary dial marked AM/PM provides a clear indication of the hour on a 24 hour basis. The single hand is driven at half the speed of the hour hand and will thus make one revolution in 24 hours
6. The time of flight is shown on a subsidiary conventional 12 hour dial situated at 6 o'clock.
7. All figures, markings and hands are white against a matt black background.
8. The movement is mounted in a large (3.25) S.A.E. case with 4 B.A. stiff nuts integral with the case. The back of the case is fitted with a corrosion inhibitor.
OPERATION
9. The clock is wound by the winding button situated at 4 o'clock. A friction overwind device incorporated in the button ensures that the mainspring or the winding mechanism cannot be damaged by overwinding.
10. The time of day hands and the AM/PM indicator can be reset by pulling out the winding button. This action stops the clock and automatically returns the sweep centre hand to zero thereby enabling the clock to be accurately set to an external time datum.
11. The action of depressing the winding button on receipt of the signal automatically starts the clock. The resetting of the time of day hands will not affect the time of flight hands.
12. The hands of the time of flight dial are inoperative while the clock
is stopped and are controlled by the three-pressure-action button, situated
at 6 o'clock, while the clock is running. The button is coupled with a flag
visible at 3 o'clock. The sequence of the button is as follows:-
(1) The first pressure starts the time of flight
hands and a black flag will be shown.
(2) The second pressure stops the time of flight
hands and a white flag will be shown.
(3) The third pressure returns the time of flight
hands to zero and a white flag will be shown.
INSTALLATION
13. The clock is secured to the instrument panel by four 4 B.A. screws on a P.C.D. of 3.5 in.