What was found
WE OPERATE/OWN 4 CITATION 680A LATITUDES FOR 5 YEARS NOW. OVER THAT TIME WE HAVE SEEN NUMEROUS FAILURES OF THE EMERGENCY ESCAPE PATH LIGHTING SYSTEM. THE FAILURE COMES DOWN TO THE EMERGENCY LIGHTING POWER PACKS. THERE ARE 4 OF THESE PACKS IN THE LATITUDE EACH PACK OPERATING A SEPARATE ZONE IN THE CABIN. TWO YEARS AGO CESSNA CHANGED THE PROCEDURE FOR CHECKING THESE POWER PACKS FROM A 3 YEAR REQUIREMENT TO A 12 MONTH INSPECTION UNDER TASK 33-50-00-961 WHICH IS A CAPACITY FUNCTIONAL CHECK OF THE BATTERIES IN THE POWER PACKS. THIS CHECK WAS REDUCED TO 12 MONTHS TO HELP REMOVE THE MEMORY OF THE NICAD CELLS. OUR OPERATION HAS SEEN A VERY HIGH RATE OF UNSCHEDULED REMOVAL OF THESE PACKS. MOST ONLY LASTING 18 MONTHS BEFORE FAILURE. BECAUSE OF THIS WE ELECTED TO SHORTEN THE INTERVAL TO 6 MONTHS TO TRY TO GET MORE LIFE OUT OF THESE PACKS AND GIVE US SOME INDICATION OF A PREMATURE FAILURE. NONE OF THIS HAS LENGTHENED THE RELIABILITY OF THESE PACKS. WHAT IS MOST DISTURBING IS THAT ONE PACK IN A ZONE CAN CAUSE A COMPETE LOSS OF THE ESCAPE PATH LIGHTING. ZONE 1 AND ZONE 4 PACKS ARE CONSIDERED TO BE ESSENTIAL PACKS. POWER FROM THE #1 PACK WILL ENERGIZE THE RELAY TO TURN ON THE ESCAPE PATH LIGHTING IN THE ARM POSITION, THE #4 PACK POWERS THE SAME RELAY FOR THE ON POSITION. IT IS POSSIBLE TO HAVE A PACK FAIL WERE IT WILL TURN ON THE EMER LIGHTS BUT DOES NOT HAVE ENOUGH POWER TO ENERGIZE THE RELAY CAUSING A SYSTEM WIDE FAILURE. THE ON POSITION IS NEVER TESTED IN THE PREFLIGHT CHECK.