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Enstrom TH-28/480 Series Maintenance Manual Supplement 8
G1000H Integrated Flight Deck System
May
14/14
Page
1-9
The GRS 77 AHRS provides the following information in ARINC 429 format:
Aircraft heading, pitch, and roll angles
Aircraft yaw, pitch, and roll rates
Aircraft body-axis accelerations
Rates of change of heading, pitch, and roll
Aircraft accelerations expressed in a local level frame of reference
The operating voltage range of the GRS 77H AHRS is from 10 to 33 volts DC. The GRS
77H AHRS provides operating voltage to the GMU 44 Magnetometer. The GRS 77H
AHRS/GMU 44 Magnetometer is capable of maneuvers through a range of 360° in bank
and pitch. The rotation rate capability is ±200° per second. However, ARINC 429 angular
rate output messages are limited to ±128° per second. Bank error and pitch error are
within ±1.25° over the range of 30° bank, left and right, and 15° pitch nose up and nose
down. Heading is accurate to within 2° in straight and level flight.
Operation in the following regions is not authorized due to unsuitability of the magnetic
fields near the Earth’s poles:
North of 72° North latitude at all longitudes
South of 70° South latitude at all longitudes
North of 65° North latitude between longitude 75° W and 120° W (Northern
Canada)
North of 70° North latitude between longitude 70° W and 128° W (Northern
Canada)
North of 70° North latitude between longitude 85° E and 114° E (Northern Russia)
South of 55° South latitude between longitude 120° E and 165° E (Region south
of Australia and New Zealand)
The GRS 77H unit is installed in the keel. See
Figure 5. Keel Mounted LRUs
. The GMU
44 unit is installed in the tailcone. See
Figure 2. G1000H System LRU Installation
Reference.
GDC 74H Air Data Computer with GTP 59 OAT Probe
The Garmin GDC 74H Air Data Computer is a remote mounted device that provides air
data for flight instrumentation. The GDC 74H requires an input from an outside air
temperature probe (the GTP 59 OAT). The system measures aircraft static and impact
pressure information from pressure transducers and raw air temperature from the outside
temperature probe. Using the raw data from the appropriate sensors, the unit computes
pressure altitude, vertical speed, airspeed values, air temperature information, and density
altitude. Aircraft specific configuration parameters are stored in an external configuration
module to make the GDC 74H an LRU. The system provides pitot static and temperature
derived air data to the GIA 63H IAU and the GDU 1040H PFD.
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