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I noticed some dots and lines on the Boeing 747 engine pylons. What are they?

enter image description here

The above image is as seen in this video at 2:18.

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    $\begingroup$ The linear objects are the strut aft fairing panel latches. The panels hinge along the dark horizontal line seen in your photo. There is an engine support strut beneath the panels. There are also hydraulic system components contained in that compartment. $\endgroup$
    – Porcupine911
    Commented Mar 19, 2016 at 19:28

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These are latches holding the engine support pylon panel in closed. Behind this panel is the diagonal brace.

This area was modified ~1992 due to the El Al Flight 1862 and China Airlines Flight 358 crashes.

See FAA Lessons Learned (via archive.is).

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I agree with the previous writer on the latches for those panels on the engine struts. Regarding some of the other objects on the strut, I'd have to hazard a calculated guess, since I've been retired off of the airplane for 10 years.

  1. the three circles are probably clear ports with glass or plastic lenses to inspect possible pressure gauges behind them without having to pull off the entire panel to read them. Most notably, they might be to read pressures of fire retardant bottles in case of an engine fire. Airline Customers might choose various configurations on things on their planes, but on our aircraft, there were two bottles per wing that could be used for engine fires.

  2. There is also a thin black line above and to the left of those circles. This is possibly a fuse pin marker. If the aircraft is normal, the line would be continuous and straight. If one of the fuse pins is broken or damaged, the black line would not line up straight and would indicate something wrong with the fuse pin inside. Fuse pins were installed on the engine struts, and at a certain temperature or stress level, they would break, allowing the engine to depart the aircraft instead of burning up the wing. We checked those markings carefully to be sure they lined up normally on each preflight, indicating all was well inside the panel. I never saw one that was misaligned, which is good!

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