Two mechanics describe how a mandatory B777-200 cargo pit fire bottle 2C test procedure and the use ...

Narrative:

While accomplishing engineering order for cargo pit fire bottle 2C check in conjunction with engineering variance; found 24.96 vdc for a split second at connector for squib for bottle 2C when fire bottle discharge switch is pushed. Write-up was made for the premature voltage found at squib connector for bottle 2C; which I found out that the same thing was found on another aircraft. Voltage was due to not having specific test equipment used in doing test and not having proper load on multimeter which was ok due to engineering order and the engineering variance; but induced the problem of the initial voltage noticed at the start. All that set aside; maintenance manual states to push the discharge switch on the cargo fire/engine control module. This starts the 20 min timer for the delayed firing of bottles 2A;B;C. When pushing the discharge switch; bottles 1A and 1B should fire. Then we disconnect test cables and move to bottles 2A; 2B; 2C and make sure that multimeters show less than .5 vdc for 19.5 mins. But if you are busy moving test cables from bottles 1A and 1B during the 20 min time that you are supposed to be checking for voltage on bottles 2A; B; and C you miss the beginning of the 20 min check for voltage and the voltage spike of 24 vdc noticed at bottle 2ABC would be missed if maintenance manual was followed the way it is written. Suggested resolution provided by submitter: 20-min timer should be restarted after test cables are moved to bottles 2A;B;C by recycling the discharge switch so the multimeters can be monitored for voltage for the full 20.5 mins; otherwise you miss the first mins of looking at bottles 2A;B;C and not knowing if the squib may have been fired when the discharge switch was first pushed. This needs to be stated in the maintenance manual. Supplemental information from acn 792331: the B777 fleet was grounded to acp the test of bottle 2C; cargo fire arm and discharge test. I was involved in the testing of the aircraft in ZZZ that day. I ran the flight deck and myself and my partner fired a bottle inadvertently. Callback conversation with reporter acn 792331 revealed the following information: reporter stated his maintenance station did not have the equipment to perform the complete amm cargo pit fire arm and discharge test. So; his carrier's engineering tried to help by writing a special authorization to shorten the amm procedure that would normally be used to perform the fire test. Reporter stated that as a result; they started the process of setting up for the test about ten steps into the normal procedure. This engineering procedure allowed them to test only fire bottle 2C. But; this shortened process only had them pulling one circuit breaker for fire bottle 2C; not the other circuit breaker's for the remaining fire bottles; including 2A and 2B. Reporter stated he believes this contributed to the inadvertent discharge of two of the engine fire bottles. Reporter believes; had they followed the initial setup at the beginning of the amm for the test; they would not have blown any bottles. There were multiple rewrites of the engineering procedure after the bottles were blown.

Original NASA ASRS Text

Title: TWO MECHANICS DESCRIBE HOW A MANDATORY B777-200 CARGO PIT FIRE BOTTLE 2C TEST PROCEDURE AND THE USE OF INADEQUATE; BUT APPROVED TEST EQUIPMENT; CAUSED AN INADVERTENT DISCHARGE OF CARGO FIRE BOTTLES.

Narrative: WHILE ACCOMPLISHING ENGINEERING ORDER FOR CARGO PIT FIRE BOTTLE 2C CHK IN CONJUNCTION WITH ENGINEERING VARIANCE; FOUND 24.96 VDC FOR A SPLIT SECOND AT CONNECTOR FOR SQUIB FOR BOTTLE 2C WHEN FIRE BOTTLE DISCHARGE SWITCH IS PUSHED. WRITE-UP WAS MADE FOR THE PREMATURE VOLTAGE FOUND AT SQUIB CONNECTOR FOR BOTTLE 2C; WHICH I FOUND OUT THAT THE SAME THING WAS FOUND ON ANOTHER ACFT. VOLTAGE WAS DUE TO NOT HAVING SPECIFIC TEST EQUIP USED IN DOING TEST AND NOT HAVING PROPER LOAD ON MULTIMETER WHICH WAS OK DUE TO ENGINEERING ORDER AND THE ENGINEERING VARIANCE; BUT INDUCED THE PROB OF THE INITIAL VOLTAGE NOTICED AT THE START. ALL THAT SET ASIDE; MAINT MANUAL STATES TO PUSH THE DISCHARGE SWITCH ON THE CARGO FIRE/ENG CTL MODULE. THIS STARTS THE 20 MIN TIMER FOR THE DELAYED FIRING OF BOTTLES 2A;B;C. WHEN PUSHING THE DISCHARGE SWITCH; BOTTLES 1A AND 1B SHOULD FIRE. THEN WE DISCONNECT TEST CABLES AND MOVE TO BOTTLES 2A; 2B; 2C AND MAKE SURE THAT MULTIMETERS SHOW LESS THAN .5 VDC FOR 19.5 MINS. BUT IF YOU ARE BUSY MOVING TEST CABLES FROM BOTTLES 1A AND 1B DURING THE 20 MIN TIME THAT YOU ARE SUPPOSED TO BE CHKING FOR VOLTAGE ON BOTTLES 2A; B; AND C YOU MISS THE BEGINNING OF THE 20 MIN CHK FOR VOLTAGE AND THE VOLTAGE SPIKE OF 24 VDC NOTICED AT BOTTLE 2ABC WOULD BE MISSED IF MAINT MANUAL WAS FOLLOWED THE WAY IT IS WRITTEN. SUGGESTED RESOLUTION PROVIDED BY SUBMITTER: 20-MIN TIMER SHOULD BE RESTARTED AFTER TEST CABLES ARE MOVED TO BOTTLES 2A;B;C BY RECYCLING THE DISCHARGE SWITCH SO THE MULTIMETERS CAN BE MONITORED FOR VOLTAGE FOR THE FULL 20.5 MINS; OTHERWISE YOU MISS THE FIRST MINS OF LOOKING AT BOTTLES 2A;B;C AND NOT KNOWING IF THE SQUIB MAY HAVE BEEN FIRED WHEN THE DISCHARGE SWITCH WAS FIRST PUSHED. THIS NEEDS TO BE STATED IN THE MAINT MANUAL. SUPPLEMENTAL INFO FROM ACN 792331: THE B777 FLEET WAS GROUNDED TO ACP THE TEST OF BOTTLE 2C; CARGO FIRE ARM AND DISCHARGE TEST. I WAS INVOLVED IN THE TESTING OF THE ACFT IN ZZZ THAT DAY. I RAN THE FLT DECK AND MYSELF AND MY PARTNER FIRED A BOTTLE INADVERTENTLY. CALLBACK CONVERSATION WITH RPTR ACN 792331 REVEALED THE FOLLOWING INFO: REPORTER STATED HIS MAINT STATION DID NOT HAVE THE EQUIPMENT TO PERFORM THE COMPLETE AMM CARGO PIT FIRE ARM AND DISCHARGE TEST. SO; HIS CARRIER'S ENGINEERING TRIED TO HELP BY WRITING A SPECIAL AUTHORIZATION TO SHORTEN THE AMM PROCEDURE THAT WOULD NORMALLY BE USED TO PERFORM THE FIRE TEST. REPORTER STATED THAT AS A RESULT; THEY STARTED THE PROCESS OF SETTING UP FOR THE TEST ABOUT TEN STEPS INTO THE NORMAL PROCEDURE. THIS ENGINEERING PROCEDURE ALLOWED THEM TO TEST ONLY FIRE BOTTLE 2C. BUT; THIS SHORTENED PROCESS ONLY HAD THEM PULLING ONE CIRCUIT BREAKER FOR FIRE BOTTLE 2C; NOT THE OTHER CIRCUIT BREAKER'S FOR THE REMAINING FIRE BOTTLES; INCLUDING 2A AND 2B. REPORTER STATED HE BELIEVES THIS CONTRIBUTED TO THE INADVERTENT DISCHARGE OF TWO OF THE ENGINE FIRE BOTTLES. REPORTER BELIEVES; HAD THEY FOLLOWED THE INITIAL SETUP AT THE BEGINNING OF THE AMM FOR THE TEST; THEY WOULD NOT HAVE BLOWN ANY BOTTLES. THERE WERE MULTIPLE REWRITES OF THE ENGINEERING PROCEDURE AFTER THE BOTTLES WERE BLOWN.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.

Attributes
ACN	792332
Time
Date	200804
Local Time Of Day	0001 To 0600
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Aircraft 1
Operator	common carrier : air carrier
Make Model Name	B777-200
Operating Under FAR Part	Part 121
Person 1
Affiliation	company : air carrier
Function	maintenance : technician
ASRS Report	792332
Events
Anomaly	aircraft equipment problem : critical maintenance problem : improper maintenance maintenance problem : improper documentation non adherence : published procedure non adherence : far
Independent Detector	other other : 1 & 2
Resolutory Action	none taken : detected after the fact
Consequence	other
Factors
Maintenance	contributing factor : engineering procedure contributing factor : manuals contributing factor : briefing performance deficiency : testing
Supplementary
Problem Areas	Maintenance Human Performance Company Aircraft Chart Or Publication
Primary Problem	Maintenance Human Performance
Situations
Publication	Cargo Fire Bottle Test

Two mechanics describe how a mandatory B777-200 cargo pit fire bottle 2C test procedure and the use of inadequate; but approved test equipment; caused an inadvertent discharge of cargo fire bottles.