TO: ALL AIRWAY FACILITIES DIVISION MANAGERS

ATTN: AIRWAY FACILITIES SECTOR MANAGERS

SUBJ: LOSS OF BEACON VIDEO WHEN POWER CYCLING STANDBY

INTERROGATOR FOR MODE S IN INDEPENDENT BEACON INTERROGATOR

(IBI) MODE

TWX: TWX-MODES-3001

DATE: 10/20/93

TWO MODE S (IBI) FACILITIES REPORTED LOSS OF BEACON VIDEO FROM

THE ONLINE INTERROGATOR WHEN THE MAIN POWER WAS CYCLED OFF/ON ON

THE STANDBY INTERROGATOR. THIS OCCURRED WHEN FOLLOWING THE

PROCEDURES IN MEASURING THE RECEIVER SENSITIVITY AND STC,

ACCORDING TO PARAGRAPH 156 IN THE DRAFT MAINTENANCE HANDBOOK

6360.XX (6365.XX). THIS CAN OCCUR WITH ANY POWER OFF/ON CYCLE OF

THE STANDBY INTERROGATOR.

THE CAUSE IS A POWER ON GLITCH FROM CERTAIN VSWR MONITOR BOARDS

(A116) IN THE INTERROGATOR, CAUSING THE VIDEO TRIGGER DRIVER

BOARD IN THE MODE S JUNCTION BOX (MSJB) TO SELECT THE WRONG

CHANNEL'S OUTPUT VIDEO.

UNTIL FINAL RESOLUTION OF THIS PROBLEM, IT IS SUGGESTED THAT

SCHEDULED DOWN TIME BE REQUESTED TO ASCERTAIN IF THIS PROBLEM

EXISTS IN EITHER CHANNEL. IF THE CONDITION DOES EXIST AT YOUR

FACILITY, PLEASE ADVISE AOS-500. FURTHER, IF THE CONDITION DOES

EXIST AT YOUR FACILITY, IT IS RECOMMENDED THAT SCHEDULED DOWN TIME

BE REQUESTED WHEN PERFORMING ANY FUTURE MAINTENANCE WHICH REQUIRES

POWER ON/OFF CYCLING OF THE STANDBY MODE S INTERROGATOR.

IF YOU HAVE ANY FURTHER QUESTIONS REGARDING THIS MESSAGE, PLEASE

CONTACT AOS-500 ON (609) 485-HELP.

EDWARD J. SCHUMAN

MANAGER, NATIONAL DATA COMMUNICATIONS

SYSTEMS ENGINEERING DIVISION, A0S-500