DDG 51 CLASS ADVISORY NR 03-93
MK 99 FIRE CONTROL SYSTEM DEFECTIVE ANTENNA FEEDHORN HEATERS
*** CANCELLED *** CANCELLED *** CANCELLED ***
REF/A/DOC/NAVSEA/-//
REF/B/DOC/NAVSEA/-//
NARR/REF A IS TECHNICAL MANUAL, NAVSEA SW273-AO-AEG-050. REF B IS PMS MIP
4829/001.//
RMKS/1. THIS ADVISORY ALERTS ALCON TO THE POSSIBILITY OF
INOPERATIVE FEEDHORN HEATERS WHICH COULD LEAD TO MALFUNCTIONING OF THE FIRE
CONTROL SYSTEM.
2. BACKGROUND. INCIDENT TO ROH FOR CG 47, RAYTHEON INSPECTED ALL OF THE MAIN
AND ANCILLARY (REAR REFERENCE) FEEDHORN HEATERS FOR THE AS-3444 ANTENNAS. A
NUMBER OF THESE HEATERS WERE FOUND TO HAVE FAILED. SINCE THESE HEATERS ARE
WIRED DIRECTLY TO SHIPS POWER AND CONTROLLED AUTOMATICALLY BY INSTALLED
THERMISTORS, THE FAILURES WENT UNDETECTED. THE ANTENNAS IN A NUMBER OF OTHER
SHIPS WERE CHECKED AND FOUND TO HAVE FAILED AS WELL. A NON-FUNCTIONING
FEEDHORN HEATER COULD RESULT IN ICE BUILDUP ON THE FEEDHORN WINDOW WHICH WOULD
CAUSE ARCING ACROSS THE WINDOW WHEN THE ANTENNA IS RADIATED.
3. ACTION.
A. DDG 51 CLASS SHIPS SHOULD PERFORM AN INSPECTION OF THE
FEEDHORN HEATERS TO ENSURE THAT THEY ARE FUNCTIONAL AS FOLLOWS:
(1) SECURE POWER TO THE HEATER BEING INSPECTED.
(2) OPEN THE INTERCONNECTING BOX ASSEMBLY (REF A,
PAGE 7-249, FIND NR 30) AND USE A MULTIMETER TO ENSURE NO VOLTAGE IS PRESENT.
(3) REMOVE WIRES FROM THE TERMINAL POST.
(4) COOL THE HEATER, USING ICE OR A FREEZE SPRAY.
(5) MEASURE THE RESISTANCE ON EACH SET OF LEADS TO EACH HEATER. AN
OPEN READING INDICATES THAT THE HEATER IS DEFECTIVE.
B. IF DEFECTIVE HEATERS ARE FOUND, PROCURE REPLACEMENTS. ON BOARD
ALLOWANCE IS ONE OF EACH (MAIN AND ANCILLARY) TYPE. CURRENT LEAD TIME FOR
MAIN HEATERS IS SIX MONTHS.
C. HEATERS SHOULD BE ORDERED USING THE FOLLOWING INFORMATION:
(1) MAIN FEEDHORN HEATER - PART NUMBER 2912010-1 NSN
4540-01-115-2545.
(2) ANCILLARY FEEDHORN HEATER - PART NUMBER 2912012-1 NSN
4540-01-264-7798.
4. FOR COMNAVSURFLANT/COMNAVSURFPAC - RECOMMEND DDG 51 CLASS SHIPS BE TASKED
TO CARRY OUT THE ACTION IN PARA THREE ABOVE.
5. NSWC/PHD IS DEVELOPING A PMS PROCEDURE FOR REF B WHICH
WILL PROVIDE A PERIODIC CHECK OF THE FEEDHORN HEATERS.
6. THIS ADVISORY HAS NO IMPACT ON EOSS, CSOSS, TECHNICAL
DOCUMENTATION OR CMP. IT WILL BE CANCELLED WHEN THE PMS PROCEDURE HAS BEEN
DEVELOPED AND DISTRIBUTED.
7. POINT OF CONTACT IS MR N S SMITHSON, PMS400F511, DSN: 332-5981 OR COMM
(703) 602-5981. TECHNICAL POC IS MR T. PETITO, NSWC/PHD CODE 4C12, DSN:
551-7377 OR COMM (805) 982-7377.//
CG-47