Instruction Manual

Page 5-24 G1000 / GFC 700 System Maintenance Manual - 200/B200 Series King Air
Revision 9 190-00915-01
Invalid Data Field
Associated
LRU(s)
Solution
HDG FAIL
GRS 77 or
GRS 7800
&
GMU 44
• Ensure metal objects (tool boxes, power carts, etc.)
are not interfering with the magnetometer and aircraft
is not in hangar, near other buildings, parked over
metal drainage culverts or on hard surfaces that may
contain steel reinforcements
• The GMU 44 magnetometers located in the tail cone
are vulnerable to magnetized rudder torque tube
lower fittings and control rod ends. This magnetism
may be caused by an improperly functioning aircraft
static discharge system which is dependent on static
dischargers (wicks) and electrical bonding of the
static dischargers and surrounding structure. The
bonding straps on the elevators and rudder should
be visually inspected to verify they are not missing,
broken or frayed. Refer to the King Air 200 Series
Maintenance Manual, chapter 23-60-00, to verify the
following items are within specification:
1. The resistance from the tip to the base of each
static discharger
2. The resistance between the base of each static
discharger and the surface to which it is attached
3. The resistance between the elevators/rudder and
the airplane structure
• Ensure that a cell phone or a device using cell phone
technology is not turned on (even in a monitoring
state) in the cabin.
• Cycle power after moving aircraft away from metal
objects to determine if metal objects were the source
of the interference. Allow up to five minutes for the
heading to reinitialize.
• Perform a Magnetometer Interference Test to check
for interference from onboard electrical system
components (e.g. NAV lights). Pay particular
attention to any new electrical devices that have
been installed since the aircraft was new. Correct
any discrepancies that do not allow this test to pass
before continuing.
• Ensure GRS 77 or GRS 7800 and GMU 44
connectors are secure.
• Check the wiring and any inline connectors between
the GRS and GMU for faults.
• Recalibrate the GMU 44,
• Load configuration files to the PFD1, PFD2, GIA1,
and GIA2
9 If problem persists replace the GMU 44.
9 If problem persists, replace the GRS 77 or GRS
7800.