A B767-300ER aircraft had leading edge asymmetry fault at the outboard slat sensor 297. Sensor replaced. Aircraft system operations checked. Aircraft released. Aircraft again had slat asymmetry fault with sensor target missing.

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Attributes
ACN	758900
Time
Date	200710
Local Time Of Day	1801 To 2400
Place
Locale Reference	airport : zzz.airport
State Reference	US
Altitude	agl single value : 0
Aircraft 1
Make Model Name	B767-300 and 300 ER
Operating Under FAR Part	Part 121
Person 1
Affiliation	company : air carrier
Function	maintenance : lead technician
ASRS Report	758900
Person 2
Affiliation	company : air carrier
Function	maintenance : technician
ASRS Report	758901
Events
Anomaly	aircraft equipment problem : critical
Independent Detector	aircraft equipment other aircraft equipment : slat asymaletry indication other other : 3
Resolutory Action	none taken : detected after the fact
Consequence	other
Factors
Maintenance	performance deficiency : testing performance deficiency : fault isolation
Supplementary
Problem Areas	Aircraft Maintenance Human Performance
Primary Problem	Maintenance Human Performance

Narrative:

Aircraft had leading edge asymmetry PIREP. Performed bite of aircraft flap/slat electronic unit. Showed outboard slat sensor fault. Troubleshot sensors in accordance with amm. Found sensor S297; faulted. Removed and replaced sensor with serviceable one; in accordance with amm. This was accomplished by 2 amt. I was observing; and assisting with information; and operation. Upon completion of installation; I operated the leading edge system in accordance with amm. Operation and chkout of the system was normal; no other faults were noted. The aircraft flew to ZZZ2 and faulted leading edge asymmetry again. It was reported that the target for sensor; S297 was missing. This was not observed when the sensor was replaced. Aircraft had a leading edge asymmetry. Found; through bite check of aircraft flap/slat electrical unit that outboard slat sensor fault. Troubleshot sensors as per sensor data.

Original NASA ASRS Text

Title: A B767-300ER ACFT HAD LEADING EDGE ASYMMETRY FAULT AT THE OUTBOARD SLAT SENSOR 297. SENSOR REPLACED. ACFT SYS OPS CHECKED. ACFT RELEASED. ACFT AGAIN HAD SLAT ASYMMETRY FAULT WITH SENSOR TARGET MISSING.

Narrative: ACFT HAD LEADING EDGE ASYMMETRY PIREP. PERFORMED BITE OF ACFT FLAP/SLAT ELECTRONIC UNIT. SHOWED OUTBOARD SLAT SENSOR FAULT. TROUBLESHOT SENSORS IN ACCORDANCE WITH AMM. FOUND SENSOR S297; FAULTED. REMOVED AND REPLACED SENSOR WITH SERVICEABLE ONE; IN ACCORDANCE WITH AMM. THIS WAS ACCOMPLISHED BY 2 AMT. I WAS OBSERVING; AND ASSISTING WITH INFO; AND OP. UPON COMPLETION OF INSTALLATION; I OPERATED THE LEADING EDGE SYS IN ACCORDANCE WITH AMM. OP AND CHKOUT OF THE SYS WAS NORMAL; NO OTHER FAULTS WERE NOTED. THE ACFT FLEW TO ZZZ2 AND FAULTED LEADING EDGE ASYMMETRY AGAIN. IT WAS RPTED THAT THE TARGET FOR SENSOR; S297 WAS MISSING. THIS WAS NOT OBSERVED WHEN THE SENSOR WAS REPLACED. ACFT HAD A LEADING EDGE ASYMMETRY. FOUND; THROUGH BITE CHK OF ACFT FLAP/SLAT ELECTRICAL UNIT THAT OUTBOARD SLAT SENSOR FAULT. TROUBLESHOT SENSORS AS PER SENSOR DATA.

Data retrieved from NASA's ASRS site as of January 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.