ALT The ashtray is actually one of my favorite engineering bits on an airplane. The design parameters for aviation all center around one thing: redundancy. If something fails, you don't want it to cause a problem. That's why planes are designed to be able to fly if an engine fails (ETOPS), there's secondary hydraulics (you'll lose functionality, but not enough to crash), there's secondary everything. Landing gear doesn't deploy? It can drop with gravity. Electrical goes out? Ram Air Turbine (RAT)! Every thing critical to flight and safety has an alternative. You're effectively flying a plane inside a plane, but don't realize it. The ashtray follows that engineering mantra perfectly. The primary method of avoiding fire is to not have cigarettes and open flames in the cabin. The secondary method is to not have flammable materials in the cabin when possible and things like an ashtray, so if someone does light up, there's less of a risk of them causing a fire (like dropping it in the trash

ALT with all the tissues). There's also smoke detectors for early detection and fire extinguishers. Even something as mundane as a no smoking policy is engineered with the thinking "what if our primary defense doesn't work?" Brilliant when you think about it. Even the smallest detail like that is thought about, and *the solution is simplistic, which is the best kind of solution for an engineering problem when safety is involved.* That's why an airline can't take off without an ashtray in the lavatory. They will actually delay a flight over it. It's a redundancy and another thing to make flying safer. Edit: obligatory thanks for the gold stranger!