Aircraft windows are rounded because the square picture windows used in early passenger planes concentrated stress on the corners. Aviation history is the process of such trial and error. The problem for investors in Boeing – which on Thursday announced that its five-times delayed 787 Dreamliner will fly by year end – is that its share price has become a bet on a series of engineering and manufacturing experiments.

Investors reacted with relief to news that the long-troubled programme required only a $2.5bn charge, sending Boeing shares up by a 10th in response. It had been feared that delays would render the company’s most successful sales effort ever entirely unprofitable – because customers start to receive compensation when their planes do not arrive on time. But management insists the Dreamliner will still turn a buck and that they can hit their self-imposed deadline to satisfy the Federal Aviation Administration that the 787 is safe.