ADS-B FDL-DB Dual Band Series
Installation Manual
Document No. 88552 Rev A
FFS Copyright © 2020 All rights reserved.
5-51
5.4
TC978 Test and Calibration
5.4.1 Local Voltage Supply Test
The TC978 Controller of the FDL-DB-XVR utilizes a DC supply voltage of 5.5V to 8V. The display
typically shows the supply voltage between 6.5V to 7.1V as shown below.
There is no option or configuration to be entered or selected in this step. Press the
ENT
button
or the
FN
button and move to the next configuration item in the setup mode.
5.4.2 TC978 Altitude Encoder Calibration
The TC978 includes a built-in altitude encoder. The TC978 Controller reports pressure altitude on
pin 4 of the DB-9 male connector on the back of the TC978 as RS-232 serial data, at 9600 bps,
using the format commonly called “Icarus” format (See Section 4.1). Section 2.7.4 provides further
details of interfacing the altitude encoder with the primary static pressure of the aircraft altimeter.
The calibrate altitude encoder setup allows the recalibration of the altitude encoder. This ensures
that the alti
tude seen on the pilot’s primary altimeter is the same as what is transmitted out of the
FDL-DB-XVR. The maximum allowed difference between the primary altimeter and the altitude
encoder is 125 feet in European Technical Standard Order (ETSO) C88a and TSO C88b. The
altitude encoder in the TC978 Controller is accurately calibrated in the factory to be within 50 feet
of the applied pressure altitude at all altitudes, whereas the allowed error in the primary altimeter
increases with altitude, and above 18,000 feet the altimeter error alone may exceed 125 feet. It
is therefore possible that the combination of the allowed errors in the encoder and the primary
altimeter may exceed 125 feet, in which case the altitude encoder must be adjusted to correspond
to the primary altimeter.
The purpose of calibrating the encoder is to make the output correspond to the
primary altimeter. The encoder calibration procedure must therefore only be
undertaken after the primary altimeter has been tested and found to comply with
the relevant standards.
5.4.2.1 Calibration Equipment
To calibrate the encoder the TC978 must be powered up and you will need a pitot-static test set
with the appropriate adapters to connect to the static port on the aircraft. The pitot-static test set
should be able to drive the altitude down to sea level, and above the service ceiling of the aircraft.
No test set is required
– the calibration procedure displays all the information you need on the
screen of the TC978 Controller.
5.4.2.2 Calibration Procedure
There are two adjustment points on the altitude encoder, a low altitude adjustment point, and a
high altitude adjustment point. The low altitude point adjusts the correspondence at sea level, and
the high altitude point adjusts the correspondence at the altitude limit of the encoder. Since the
