Specifications

SECTION III
INSTRUMENTATION AND AVIONICS
MODEL 560
DIGITAL CLOCK
One model M877 digital clock is mounted on the left side of the pilot’s instrument panel and one on
the right side of the copilot’s panel. The clock can be made to display four time functions: local time, GMT,
flight time and elapsed time. Two versions of the elapsed time function may be selected: count up or count
down. The clock has two control buttons: SEL (select) and CTL (control). The SEL button is used to
select the desired function, and the CTL button to start and reset the selected mode.
For normal operation, either local time or Greenwich Mean Time (GMT) may be selected. GMT is
displayed only in 24-hour format, and local time is 12-hour format. Pressing the SEL button sequentially
displays GMT, local time, flight time and elapsed time. The displayed mode is annunciated GMT, LT, FT
and ET, as applicable, under the time display window. To set GMT or local time, select the desired
function by pressing the SEL button. Simultaneously press both the SEL and the CTL buttons to enter the
set mode. The tens of hours digit will start flashing and may be incremented by pressing the CTL button.
The next digit is then selected by pressing the SEL button, and similarly set by means of the CTL button.
When the last digit has been set, press the SEL button to exit the set mode. At that time the clock will start
running and the lighted annunciator will resume flashing. When no airplane power is applied to the clock,
the SEL and CTL buttons will not operate.
To use the clock as a stop watch to time approaches, etc., select ET with the SEL button and press
the CTL button to start the timing. The clock will start counting elapsed time in minutes and seconds up to
59 minutes and 59 seconds. It will then switch to hours and minutes and continue up to 99 hours and 59
minutes. Pressing the CTL button will reset the elapsed time to zero. To use the clock for an elapsed time
"count down" display, select ET for display and enter set mode by pressing both buttons simultaneously. A
maximum count down time of 59 minutes and 59 seconds can be set. The time from which it is desired to
count is entered in the same manner as setting GMT or local time. When the last digit is set, press the
SEL button to exit the set mode. Pressing the CTL button will start the countdown. The display will flash
when the time reaches zero. After reaching zero, the ET counter will count up. Pressing the CTL button
again resets ET to zero.
A flight time alarm mode is provided which will flash the clock display when the desired flight time is
reached. To set the alarm function, select FT with the SEL button and enter the set mode by pressing both
buttons simultaneously. Enter the desired alarm time in the identical manner that GMT or local time is set.
When flight time equals the alarm time, the display will flash. If FT is not being displayed when the alarm
time is reached, the clock will automatically select FT for display. Pressing either the SEL or CTL button
will turn off the alarm and reset the alarm time to zero. Flight time is unchanged and continues counting.
The clock display may be tested when power is on the airplane by holding the SEL button down for
three seconds. The display will show 88:88 and activate all four annunciators.
Figure 3-8. Digital Clock
I 3-16 Configuration AA 56OMB-01