So there I was, sitting in a nice window seat of a Boeing 737, idly minding my business while the crew taxied. We would be using 34R out of Salt Lake City, a runway I have used many times as a pilot.
"Folks, it looks like we're number one for departure. Flight attendants do your thing."
We whip around onto the runway, and as we do so I notice that there is a loose latch on one of the nacelles. I'm not even remotely qualified in the 737 but it looks like an access door of some kind. It's one of those two-step latches on which you push a button, then fiddle to get it open. The picture is from a different flight on a different airline, but you can see the latch at the far right.
What do you do?
We were already rolling, and I quickly realized that whatever the right thing to do was, I would have no influence on the outcome. They're not gonna abort for a passenger calling an aircraft defect, and even if they were by the time the word got up front the airplane would be near V1 and it would be too dangerous.
The inspection door stayed on through the flight. As we deplaned I told the FO about it, and even gave him an out ("it's on top, you wouldn't see it during a walk-around.")
Would the NTSB have blamed me if it had come off in flight? I'm reminded of a scene many years ago, standing on the ramp with my jaw dropped watching my buddy land his Mooney gear-up with absolutely no way to stop the accident. But it's not about blame; I only wish that I could have helped.