S-TEC ST 360 ALT, Pilot Operating Handbook

2nd Ed.  Jan 15, 08

3-3

S–TEC

3.1 Selector / Alerter Operation

3.1.1 Data Entry

Press the DTA switch, such that ENT is annunciated.  Any of the following
quantities can now be entered into the Selector / Alerter:

Barometric Calibration (reference section 3.1.2)

Selected Altitude (reference section 3.1.3)

Selected Vertical Speed (reference section 3.1.4)

Selected Decision Height (reference section 3.1.5)

Whenever ENT is annunciated, the Selector / Alerter is decoupled from the
autopilot.  In that case, if the Selector / Alerter happens to have vertical speed
command authority as indicated on its display, then the autopilot will hold the
aircraft at the last selected vertical speed.

Once the particular quantity has been entered, press the DTA switch again to
make it operational.  The ENT annunciation will extinguish as a result.

Note:

It is not necessary for ENT to be annunciated, in order to enter vertical speed
selection changes.

3.1.2 Barometric (BARO) Calibration

The true altitude is the altitude above Mean Sea Level (MSL).  The output of an
Encoding Altimeter / Blind Encoder is the altitude expressed as a digital Gray
Code, relative to the standard barometric pressure of 29.9 inches of mercury
(inHg) or 1013 millibars (mb).  This output is known as the encoded altitude.

When the Altimeter is set to the true altitude, the barometric pressure at MSL will
be shown on its Kollsman scale.  The Selector / Alerter must then be calibrated
to the Altimeter.  This is accomplished by changing the barometric pressure
setting on the Selector / Alerter to match the Kollsman scale.  As a result, the
encoded altitude at the input of the Selector / Alerter is internally converted to the
true altitude, for use in making computations.

Following the power-up self test (reference section 2.0), the barometric
pressure setting is 29.9 inHg, and ready to be changed to match the Kollsman
scale.  Rotate the Modifier Knob clockwise (CW) to increase the barometric
pressure setting, or counter-clockwise (CCW) to decrease the setting.  Each
detent changes the setting by 0.1 inHg, regardless of whether the Modifier Knob
is pushed-in or pulled-out.

The units of barometric pressure can be changed from inHg to mb, by pressing
the BAR switch.  Each CW or CCW detent of the Modifier Knob changes the
barometric pressure setting by 1 mb, regardless of whether the Modifier Knob is
pushed-in or pulled-out.  When the setting is greater than 999 mb, the
one-thousand digit is not shown.  For example, a setting of 1013 mb would
appear only as 013.  The units of barometric pressure can be changed back to
inHg, by pressing the BAR switch again.