Maintenance technician reported that the fan cowls on #1 engine appeared to be properly latched clos...

Narrative:

I was performing maintenance to the #1 left/H engine; specifically to [a B737]. One of the maintenance tasks required the #1 engine left/H outboard cowl to be open for idg [integrated drive generator] servicing. I noticed no issues opening the cowl. Later that evening I closed and latched the same cowl. Later that night I again checked the engine oil cap and cowl security as I normally do; noticing no issues; to the best of recollection; specifically to the latching security of the #1 left/H engine fan cowl. I had only the forward hold open rod engaged; and rested the cowl against my body for a minute or two while stowing the hold open rod. I lowered the cowl door with no issues; later I moved to the ground and latched the center; forward; and then aft latch. I recall dripping oil splattering lightly on my head from the forward latch closing and using my jacket to wipe my forehead. When opening cowl I clicked the all three hooks into the handle for clearance purposes when closing. Pins; hooks and handles appeared normal. All three latches closed nicely; good torque and a nice secure click when shut. I noticed nothing wrong and was not distracted in any manner. I checked the #1 engine cowl latches more than once later that evening and latches were secure.

Original NASA ASRS Text

Title: Maintenance Technician reported that the fan cowls on #1 engine appeared to be properly latched closed after he had performed maintenance; but the cowling apparently later opened in flight.

Narrative: I was performing maintenance to the #1 L/H engine; specifically to [a B737]. One of the maintenance tasks required the #1 Engine L/H outboard cowl to be open for IDG [integrated drive generator] servicing. I noticed no issues opening the cowl. Later that evening I closed and latched the same cowl. Later that night I again checked the engine oil cap and cowl security as I normally do; noticing no issues; to the best of recollection; specifically to the latching security of the #1 L/H engine fan cowl. I had only the forward hold open rod engaged; and rested the cowl against my body for a minute or two while stowing the hold open rod. I lowered the cowl door with no issues; later I moved to the ground and latched the center; forward; and then aft latch. I recall dripping oil splattering lightly on my head from the forward latch closing and using my jacket to wipe my forehead. When opening cowl I clicked the all three hooks into the handle for clearance purposes when closing. Pins; hooks and handles appeared normal. All three latches closed nicely; good torque and a nice secure click when shut. I noticed nothing wrong and was not distracted in any manner. I checked the #1 engine cowl latches more than once later that evening and latches were secure.

Data retrieved from NASA's ASRS site 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	1688285
Time
Date	201909
Environment
Flight Conditions	VMC
Aircraft 1
Make Model Name	B737-800
Operating Under FAR Part	Part 121
Flight Phase	Initial Climb
Flight Plan	IFR
Component
Aircraft Component	Cowling/Nacelle Fasteners Latches
Person 1
Function	Technician
Qualification	Maintenance Powerplant Maintenance Airframe
Events
Anomaly	Aircraft Equipment Problem Critical Deviation - Procedural Maintenance Deviation - Procedural Published Material / Policy

Maintenance technician reported that the fan cowls on #1 engine appeared to be properly latched closed after he had performed maintenance; but the cowling apparently later opened in flight.