The upper portion of the door has both outside
and inside locking handles connected to a
common shaft through the door. Rotating ei-
ther of these handles to the closed position
drives six locking pins into holes in the fuse-
lage frame (Figure 1-10) (three pins forward
and three aft) and two pins through interlock-
ing arms that secure the two door halves to-
gether.
The lower door has a single locking handle on
the inside. Rotating the lower door handle to
the closed (forward) position drives two pins
into holes in the fuselage frame (one forward
and one aft). There are a total of 10 locking
pins on the two door sections.
To facilitate engagement of the upper door
locking pins during closing, an electric actu-
ator motor, torque tube assembly, and one or
two hooks are installed in the lower door which
engage rollers installed on the upper door. The
actuator motor is operated from inside the air-
plane by a toggle switch on the lower door, and
from the outside by a key switch. Excluding
those airplanes subsequent of SNs 24-294 and
25-170 and those with replacement motors,
should the motor fail, the hook(s) can still be
operated manually from inside. Access is pro-
vided to the torque-tube mechanism through a
panel in the lower door, and a ratchet handle
provided in the airplane tool kit can be used to
operate the torque tube manually.
NOTE
One hook is used on 24-inch doors,
while two hooks are used on 36-
inch doors.
A secondary safety latch is installed on the
lower door and is separate from the door lock-
ing system. It consists of a notched pawl at-
tached to the door. The pawl engages a notched
striker plate attached to the frame when the
door is closed. This engagement holds the lower
door closed while the locking handle is being
positioned to the locked position. Additionally,
it prevents the door from falling open as soon
as the door handle is opened. The latch is re-
leased by depressing the pawl.
When closing the doors from the inside, close
and latch the lower door first. Then, close the
upper door and actuate the door motor switch
to the closed position. This engages the hook(s)
over roller(s) in the upper door, and cinches
the upper door down tight while allowing the
locking pins to line up properly and meet the
microswitches as the upper door handle is ro-
tated to the closed position. The DOOR light
will remain illuminated until the hook(s) are
backed away from the upper door rollers by re-
verse operation of the door motor switch.
When the door handles are in the closed posi-
tion, the pins all contact microswitches. If any
of the switches is not actuated, a red DOOR
light illuminates on the annunciator panel (see
“Annunciator Panel” section). If the light illu-
minates while the door is closed, the pilot can
visually check through inspection ports for
proper alignment between the white lines on
the latch pins and on the door structure. The
two latch pins which connect the upper and
lower doors are visible through the upholstery
gap at the interface and do not have white lines.
Cables and hydraulic dampers are provided to
stabilize the lower door when lowering it and
when using it as a step. The 24-inch door has
one cable and a hydraulic damper. The 36-
inch door has two cables and may have an op-
t i o n a l h y d r a u l i c d a m p e r. T h e c a b l e s a r e
connected to takeup reels in the lower door and
1-10
FOR TRAINING PURPOSES ONLY
LEARJET 20 SERIES PILOT TRAINING MANUAL
FlightSafety
international
Figure 1-10. Door Locking Pin Hole