A Rolls-Royce engine blows up, and … silence — for four days. The great British engineering company took its time to find out what had happened to the Trent 900 engine mounted on the wing of a Qantas A380 superjumbo, which had to make an emergency landing in Singapore a few days ago. The company preferred to offer facts rather than speculation. Its brief statement on Monday, declaring that progress was being made in the investigation, calmed investors, initially. By Friday it had identified the faulty component. So not too much harm done. Probably.