Fiber Optic Gyro System (FOGS) (AHRU) New Equipment CN-1716/A Fiber Optic Gyro System (FOGS) Attitude Heading Reference Unit (AHRU)

CN-1716 (FOG) New Equipment will replace the three existing gyros ASN-43(Direction Gyro) CN-1314 (Vertical Gyro) and TRU-2A/A (Rate Gyro)

What is AHRU? The Fiber Optic Gyro System (FOGS) is a Attitude Heading Reference System (AHRS) that provides accurate aircraft pitch, roll, magnetic heading, and turn rate information for integration within an avionics subsystem.

How FOGS Work Fiber Optics for Axial Reference replacing the mechanical gimbaled gyros. Accelerometers electromechanically compensate & stabilize in flight AHRU is a self latitude look up system. Flux Valve provides initial reference in heading FOGS filters fluctuations of flux valve which smoothes out the pitch, roll, and heading output.

“FOGS” AHRU CN-1716/UH-60 Gyros Replacement New Digital Control Improved display and control capability Improved maintenance and diagnostics functions Spec Mean Time Between Failure: 6000 hrs. Manufacturer Predicted MTBF: 15,000 hrs) Significant Simplification of Compass Alignment (you don’t do anything!) Improved Navigational Accuracy

NAVIGATION SET, AN/ASN-128 HSI VSI AFCS Interconnections FLUX VALVE NAVIGATION SET, AN/ASN-128 HSI VSI AFCS

Supplies information to Doppler in the absence of GPS. AHRU and ASN-128 AHRU is not a navigator. Supplies information to Doppler in the absence of GPS. Improves accuracy of ASN 128

Before

After CN 1716 CN 1716

AHRU (FOGS) AHRU AKA: FOG, SUE, MDU, Lisa.... OUTPUTS Digital Arinc-429, RS-422: (Heading, Pitch, Roll, Body Rates & Accelerations, Vertical Velocity) Synchro Arinc-407: (Heading, Pitch, Roll) Analog: (Yaw Rate, Validities, 2 Wires Attitude, Interlock for Autopilot) ACCURACY Heading: 0.8 deg. Attitude: 0.5 deg

SENSOR ELECTRONIC UNIT (SEU) GENERAL VIEW

“SEU” aka “FOG” AHRU CN-1716/A

Before Compass Controller

After

DIGITAL CONTROL PANEL (DCP)

CCAL = Compass Calibration Digital Control Panel Display Window DG MODE (FREE) Indicator CCAL MODE Indicator Alignment Mode Indicator Failure Indicator SLAVED MODE Indicator MODE Selector Function Selector Display Cursor Movement Enter Selection Button CCAL = Compass Calibration

!! The LOWER CONSOLE lights HAVE to be ON !! SEE the LIGHTS !! The LOWER CONSOLE lights HAVE to be ON !! When are we in the 1-212th going to turn the lights on? Anytime you need info off the DCP and you can’t see it. It will be acceptable to turn them on during Circuit Breakers and Switches – Set.

!! LOWER CONSOLE lights have to be ON !! AC Power Applied Initial power on: All lamps illuminate for 2.5 seconds. !! LOWER CONSOLE lights have to be ON !! - DCP performs a lamp self-test / system MOC.

Turn Lower Console lighting rheostat on to illuminate DCP. NO DISPLAY? Turn Lower Console lighting rheostat on to illuminate DCP.

AC Power Applied ALN lamp will be on Initial power on: DCP is performing lamp self-test for 2.5 seconds, THEN: ALN lamp will be on ATT fail flag on the VSI will be in view AHRU will align and self-test within 45 seconds

AC Power Applied After 45 seconds: the SYSTEM will automatically default to the SLAVE mode and the VSI ATT warning flag disappears

BIT STATUS:FOG FAIL ! If the FAIL lamp appears – The Display Window will show two BIT words: a. LRU/SRU information and b. the failure code. (Write up “AHRU Failed x amount of times”. It is not necessary to write up the failure BIT info/code.) The CDU stores the last 16 faults.

Starting Procedure Step 1. Mode Selector – As desired. (you always desire SLAVE while you are at FT Rucker) a. The Lower Console Lights have to be on for the lights on the DCP to be seen. b. The default mode is SLAVE – Therefore, you should not have to move, touch or otherwise fondle anything for it to be in the SLAVE mode.

Step 1. Mode Selector – As desired. (Continued) Starting Procedure Step 1. Mode Selector – As desired. (Continued) Do Not select anything other than SLAVE! Do Not select DG unless you are above 70° Latitude (Be sure you have CAO approval to be out of the LFA) THOU SHALL NOT select CCAL!!

Call Maintenance Starting Procedure Step 2. HSI – Check to see that HSI heading agrees with a known magnetic heading [STANDBY (Magnetic) COMPASS]. If the HSI does not line up after the 45 second alignment time + your patience - Call Maintenance

Failures If a failure is detected, the FAIL lamp will illuminate, and the display window will show a message indicating which AHRU has failed. Press Enter to clear the fail light If the fail light clears – continue mission If fail light does NOT clear – CALL MAINTENANCE

ELECTRICAL POWER CHARACTERISTICS A Primary power interruption of less than 200 milliseconds does not cause a system realignment. Power interruptions more than 200 Milliseconds CAUSE SYSTEM IN-AIR RE-ALIGNMENT The ATT and HDG warning flags will be in view to indicate the system is doing a re-alignment. DURING THE RE-ALIGNMENT PHASE, MAINTAIN STRAIGHT and LEVEL UNACCELERATED FLIGHT (2.5 to 45 seconds)

“Hold the Controls” NOTE During aircraft shutdown, when engine power control levers are moved from the Fly to Idle position, or when the generator switch position is changed to off, and electrical power assignment is changed from Main Generator to APU Generator, an un-commanded right or left pedal drive of up to ¼ inch may occur, returning to neutral position within 3 seconds.

If the Collective Position Sensors are out of null CLTV NULL = YAW DRIFT If the Collective Position Sensors are out of null the aircraft will have a greater tendency to YAW at a HOVER than with the older system.

especially if you have seen the fail light on the DCP. YAW DRIFT If the YAW DRIFT is more than you are accustomed to or otherwise seems abnormal – Write it up, especially if you have seen the fail light on the DCP.

GYRO ERECT IN SLAVE MODE FAST ERECT SYNC may be activated in air to perform a fast Heading error resetting in a magnetic sterile area.

This is a MAINTENANCE FUNCTION CCAL This is a MAINTENANCE FUNCTION Don’t go there!!

COMPASS CALIBRATION MODE Lest ye be tempted Once CCAL begins it MUST be completed!!! (You don’t know how) CCAL is ONLY used on ground. You CAN NOT get out of CCAL using the MODE select button!!! HOLD THE CONTROLS!!!!!! (you don’t know why but it can be ugly!) FOGS CAN NOT BE ZEROIZED after initial calibration.

COMPASS CALIBRATION (CCAL) MODE IN CCAL MODE THESE FUNCTIONS ARE ENABLED: COMPASS CAL START COMPASS CAL STORE COMPASS CAL COEFFICIENTS READ COMPASS CAL COEFFICIENTS WRITE BIT STATUS REQUEST BIT HISTORY REQUEST INDEX SET REQUEST (NEVER EVER CHANGE!!!) ETI GET REQUEST If you don’t know what this means – why are you in CCAL?

GO FLY!!! Summary Turn on Lower Console Lights Be sure MODE is SLAVE Be sure HSI heading agrees with a known magnetic heading GO FLY!!!