Sir John Harvey Jones spent 26 years working his way up ICI from management trainee to chairman.
Sir Roy McNulty, the executive chairman of CAA before the role was split in two and occupied by two non aviation people was a fully paid up aviation professional who had worked at Shorts and NATS.
Both knew the business and industry sectors intimately.
That's the difference. You don't need to be a chemist to understand the chemical engineering business, or a pilot to understand the aviation business. But you do need to understand the business.
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