North Wing S-LSA Maintenance Manual
Model: Scout 912
Version 3.2
Release date 04-16-2014
Page 70
from the charging coils to the switch is broken, the mag switch cannot ground out the engine
ignition and the engine will continue to run. Since there are two independent ignition systems,
the failure of only one switch will allow the engine to continue running on that ignition
system, and without special tools, it is not obvious which switch has failed. The table below
shows the results of different combinations of switch positions and conditions.
For Pilot Switches Only:
Pilot Switches
Results
Ign. A
Ign. B
On
On
Engine runs on both ignition systems
On
Off
Engine runs on Ignition system A only
Off
On
Engine runs on ignition system B only
Off
Off
Engine will not run
Fails Open
Off
Engine runs on ignition system A only
Off
Fails open Engine runs on ignition system B only
In the 2 cases above where the switches fail open, the only way to shut the engine down with a
failed switch is to either choke it or, if possible, starve it by pinching the fuel line until the
engine stops. Fuel shut offs are not provided on North Wing aircraft because of the high
probability of someone forgetting to open it but still having enough fuel in the carburetor to
get off the ground.
With Instructor Switches Installed:
Pilot Switches
Instructor Switches
Results
Ign. A
Ign. B
Ign. A
Ign. B
On
On
On
On
Engine runs on both ignition systems
On
Off
Off
Off
Engine will not run
Off
Off
On
On
Engine will not run
On
Off
On
Off
Engine runs on ignition system A only
Fails Open
Off
On
On
Engine runs on ignition system A only
Off
Fails Open
On
On
Engine runs on ignition system B only
Off
Fails Open
On
Off
Engine will not run
Note that with the instructor switches installed, the ignition system with the failed switch can
still be turned off unless the failure is in the leads coming from the engine to the Hot Box. A
properly functioning “OFF” position overrides the ON position because it is able to ground out
the ignition coil, thereby making that ignition coil inoperable.
Once the engine is stopped, trace the ground and yellow coil wiring to the mag switches using
an Ohm meter or continuity meter to assure they are indeed grounded when the mag switch is
in the OFF position. Locate and repair the break in the ground circuit.
