Good points Pongo with regard to the 170k Boeing employees, very few, outside of the navigation systems guys, would need to know.
But let's look at the pilots who all definitely would have to know about a flat earth.
According to Wiki, there are 95,000 passenger flights per day. Each flight has a crew of at least 2 for domestic flights and 4 to 6 for international flight. So let's use an average of three flight crew members per flight and many are back and forth, so guestimate 150,000 to 200,000 pilots and copilots flying every day. That's a lot of people sworn to secrecy Have you ever heard a pilot break the big news that the planet is actually flat?
I've heard many of the become whistle blowers regarding safety and training issues, but never one confession that the world is actually flat...hmm.
Seems somebody's really got all those people committed to this secret.
Or, the more obvious conclusion is the world is not flat.
Probably similar or bigger numbers for ship captains and ship navigators, not to mention private sailors.
Occam's Razor... simplest explanation is almost invariably correct.