No sooner had British Airways Flight 9240 roared into the air over Heathrow Airport than the cabin air was pierced by a sharp, scary noise, like an alarm or a siren. The power surged and then seemed to falter, and the plane became worryingly quiet. (Too quiet?) What was it? Images of catastrophic scenarios — birds, engine failure, parts falling off, total systemic breakdown — pinballed through the passengers’ imaginations as the plane seemed to struggle to find its equilibrium. Unease gripped th