Century Flight Systems, Inc. logo, Auto Pilots and Aircraft Instrumentation
Call Century Flight Systems: 1-800-433-5630

Find Century Flight Systems on FacebookFollow Century Flight Systems on TwitterWatch Century Flight Systems on YouTubeSubscribe to Century Flight Systems RSS Feed

Compass System Features

Compass System FeaturesWhat is an HSI?

An HSI, or Horizontal Situation Indicator, is a combination of two familiar cockpit instruments: the directional gyro with a heading bug and a VOR/ILS indicator.

What does an HSI do for the pilot?

Combining the directional gyro and the NAV indicator into one instrument reduces pilot workload by providing heading, course reference, course deviation, and glideslope information all in one visual aid. In addition, an HSI:

  • Makes it easier to visualize the aircraft's position with reference to the selected course or holding patterns. The "split needle" presentation, made up of the course and reciprocal pointers and the VOR/LOC deviation indicators, clearly shows both selected course and course deviation.
  • Gives standard sensing and course deviation indication on back course ILS approaches, provided the front course heading is set under the head of the course pointer and the plane is flown toward the course deviation indicator.
  • Provides convenient 45-degree tic marks to help visualize procedure turns and reciprocals so that pilots need not memorize outbound/inbound headings or add/subtract 45 degrees for intercepts or offsets.
  • Serves as a heading bug for autopilot coupling or as a heading reminder in aircraft not equipped with autopilots.

Compass System Working Parts

Heading Select Knob: Rotating this knob sets the heading bug and also aligns a heading transformer for coupled autopilot use to the selected heading. Pushing this knob in cages the gyro.

Heading Flag: This red warning flag indicates loss of vacuum and/or electrical power to the gyro. Heading information is then unusable, but all course information (comparable to a standard VOR/ILS) remains valid.

Course Select Knob: Rotating this knob sets the course pointer to a selected course, and if so equipped, a course transformer for coupled autopilot use.

Course Pointer: This pointer indicates the selected course. Turning the course select knob will rotate the course pointer (VOR/LOC deviation indicator) and course reciprocal around the compass card. As the aircraft's heading changes, the course pointer rotates with the compass card to indicate the difference between the course (under the course pointer) and the actual aircraft heading (under the lubber line). The course selector may also be coupled to an autopilot or flight director. When coupled, "off course" signals are generated which direct the autopilot to maintain or acquire the selected course.

VOR/LOC Deviation Indicator: The center portion of the course pointer needle moves to indicate deviation from selected course. A series of dots provides a linear indication of how far the aircraft is off course. Each dot represents a percentage of the total course width. In VOR use, the course width is a total of 20 degrees, 10 degrees either side of center. When being used to fly the localizer, it shows runway center line and percentages of the total course width which is 2-1/4 either side of center. In either case, the actual linear distance off course depends upon the distance from the station. When used to display RNAV or LORAN, each dot will represent a percentage of the total course width in miles. An "on course" condition is indicated when the course pointer, the course deviation bar, and the course reciprocal are all in line.

To-From Indicator: This indicator is a white triangle and appears underneath the VOR/ILS deviation indicator. It shows whether the selected course will take the aircraft either to or from the VOR station.

Reference Aircraft: Representing the actual aircraft, this symbol is fixed and is located in line with the lubber line. Lubber Line: This orange line, located at the top of the display, indicates the aircraft's magnetic heading on the compass card. The lubber line is in line with the reference symbol to reinforce this association.

Compass Card: This card, located beneath the lubber line, indicates the aircraft's current heading. The card is mechanically coupled to the compass card set knob and, at the beginning of each flight, must be set by the pilot to agree with the magnetic compass heading or to the slaving meter, if installed. As the flight progresses and headings change, the directional gyro rotates the card to indicate the current heading. As with any standard unslaved DG, some gyro precession will occur. Therefore, it is necessary to check and reset the compass card at periodic intervals.

Slaving Meter: A slaving meter is located in the upper right-hand corner of the instrument face on slaved models. If equipped with a slaving feature, an HSI will automatically update its compass card with a magnetic sensor to correct for precession. In flight, the meter needle will oscillate slowly when the compass card is properly aligned with the magnetic compass.

Heading Bug: The selected heading is marked by an orange heading bug which can be moved to any point about the perimeter of the compass card. As the aircraft's heading changes, the bug rotates with the compass card, thus alerting the pilot to the difference between the selected heading (located under the bug) and the actual aircraft heading. The heading bug may also be coupled to an autopilot or flight director system. When coupled, "off heading" signals will be generated causing the autopilot to fly the aircraft so as to maintain the selected heading.

NAV Flag: This red warning flag indicates inadequate VOR or LOC signal or loss of power to meter circuits. Under these conditions, course information is unusable; however, all heading information remains valid.

Glideslope Deviation Indicator: This yellow wedge relates the vertical glide path centerline to the aircraft's position. The aircraft is "on glide slope" when the wedge covers the horizontal index. Each dot on this vertical scale represents approximately 0.4 degrees vertical deviation from the centerline. An up deviation is a fly up command while a down deviation means to fly down in order to place the aircraft "on glide slope."

Glideslope Mask: This mask will cover the glide slope deviation indicator in the absence of a usable signal or when a VOR frequency is selected.

Compass System Specifications

HSI Compass System SpecificationsCentury HSIs help pilots spend less time worrying about the complexities of navigating the aircraft and more time enjoying the freedom of flight.

By seeing your position graphically, you receive accurate data at a glance, helping you to navigate confidently and easily in any condition.

Choose from four of the world's best-selling HSI models:

NSD360A Slaved HSI

  • The most popular HSI on the market today.
  • The best features available in an HSI.
  • Simplistic operation.

NSD360A Slaved HSI with RMI Bootstrap

  • The top-of-the-line Century pneumatic HSI.
  • Provides accurate heading information to other flight instrument displays.

NSD360A Non-Slaved HSI

  • The most competitively priced pneumatic HSI on the market today.
  • Defines cost-effective HSI performance.


  • The new standard in electric HSIs.
  • The only electric HSI that does not require a remote gyro.
  • Combines the power of a remote, with the light weight, reliability, and simple installation of a self-contained, one-box instrument.
  • Slaving is a standard feature.
  • RMI bootstrap is optional.

Features of Century's HSIs

  • The most competitively priced pneumatic HSI on the market today.
  • Built-in Electric Gyro (NSD1000 only)
  • Full-time 360-Degree Heading Presentation
  • Rectilinear Course Deviation Indicator
  • Full View Glideslope Indicator
  • Masking Glideslope Warning Flag
  • Built-in Slaving Indicator *
  • 45-Degree Tic Marks
  • Referencing Heading Bug
  • Failed Gyro Warning Flag
  • Free Gyro Mode
  • Gyro Caging Knob
  • Lost Power Warning Flag
  • Discrete NAV Warning Flag
  • RNAV and LORAN Compatible
  • Automatic Magnetic Gyro Slaving *
  • Autopilot Outputs for Heading and Course
  • Continuously Caged Heading and Course Selection Knobs
  • Reference Aircraft and Heading Lubber Line
  • Diffused Incandescent Perimeter Lighting
  • Course Arrow with Reciprocal Indicators
  • TSO's C5e, C6d, C9c, C52a

Dimensions and Weight

  • Height: 3.38 inches
  • Width: 3.38 inches
  • Panel Cutout: 3-ATI
  • Depth: 8.69 inches (NSD360A gyro port and fitting not included.)
  • Weight: 4.6 lbs. (instrument only)

Power Requirements

  • 14 or 28 VDC (NSD1000)

Note: The NSD1000 is voltage specific.


  • Connector Kit
  • Slaving Amp or Slaving Bootstrap and Flux Detector *

Note : * = Slaved models only.

Altitude Preselect/Alerter

Altitude Preselect/AlerterThe Digital Altitude Preselect (DAP) is available for the Century 2000 and Century 41 autopilot systems. It provides the dual function of preselected altitude and an audible tone. It receives altitude information from the aircraft encoding altimeter or blind encoder. The DAP is very easy to program for it's five modes. As the aircraft approaches to within 1,000 feet of the selected altitude the display will flash and give two audible tones. Upon closure of 200 feet from the selected altitude, the display stops flashing and gives one audible tone. At the selected altitude the autopilot will smoothly transition from Arm to Alt Mode to display current encoder altitude.

The five position selectable switch gives you the following modes:

  1. Altitude Readout
  2. Radar Altimeter Setting
  3. Adjustable pixel dimming
  4. Barometric/Millibar Setting
  5. Altitude Select/Arm Setting

The radar altimeter is optional if the aircraft has a radar altimeter. If not, this mode can be ignored.

DAP General Information

Height: 1.45 inches
Width: 3.17 inches
Depth: 9 inches
Panel Cutout: 1.5 inches x 3 inches ATI
Weight: 1.345 lbs.
Power Requirements: 14 or 28 VDC
Accessories: Connector Kit
Inputs: Pressure altitude data from encoding altimeter or blind encoder with ATC format (100 ft. resolution) or RS232 serial data (1 ft. resolution).

Century I Autopilot

Century I AutopilotCentury I is an all-electric, rate-based, lightweight, single axis, roll/heading lateral stabilization autopilot. Vacuum system failures will not affect the operation or performance of the Century I. An electric servo on the aileron control system provides the control force for the wing-leveling stabilization and pilot-commanded, knob-controlled turns at rates of up to 200°/minute.

The system utilizes a tilted rate gyro to sense rate of turn and roll rate in its 3-inch lighted standard turn indicator. The indicator includes an inclinometer (ball) for slip/skid indications, and VOR/LOC radio signal tracking is standard. The Century I may also be used as an all-electric safety backup autopilot to the Century IIB, III, or IV vacuum/electric systems, sharing the same roll servo. Unlike many competitive systems, the custom-manufactured cable harness is included to reduce installation time and expense.

Options: Stand-alone manual electric trim is certified in some aircraft.

Century I General Information


Weight: 7 lbs.
Power: 1.25 amps @ 14 or 28 VDC
Panel Size: 3.5"W x 3.5"H x 7.64"L



Century I Packages

AK ( ) Kit is priced complete with all necessary installation hardware, brackets, and manufactured electrical cable harness.


NOTE: Some systems have special requirements or set-up costs resulting in higher prices.

KitsDescriptionSuggested List Price
Century IBasic Autopilot Kit, 52D75-4M, 14V, Turn and Bank Instrument with Amplifier and Radio Tracker (lighted).      CALL
Century IBasic Autopilot Kit, 52D75-4M, 28V, Turn and Bank Instrument with Amplifier and Radio Tracker (lighted).      CALL
AK 319Retrofit Radio Tracker Kit for older units       CALL
s aircraft logo excellence
s autopilot century4000
s yaw damper
s compass system
s servo