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PEI_3721 - I was looking at a MAX video and noticed, next to the usual big strake at about 10 o'clock on the center of the cowling, a set of 2 smaller longitudinal white painted vanes/strakes on the inside of the engine on the sliding part of the thrustreversers. When the reversers slid back after TD, the vanes/strakes did not hit the leading edge of the wing, because a kind of small 'trapdoor' opened upward to let them pass through. On sliding forward the vanes/strakes became visible again and the 'trapdoor' closed behind them. Would be interesting to hear from you what their purpose is in the aerodynamic context that you were just posting about ;-)