the reason BA suffered an IT crash comes down to two reasons, sadly, not unique to BA or the travel industry.
Firstly, systems are simply built to a lower-order engineering standard than they were 30 years ago. This combined with the vast interconnectivity that exists in modern infrastructure causes interdependencies that can lead to catastrophic failure (such as the recent BA example) without any likely chance of prior discovery. For an example of this reduction in engineering tolerance, look at the humble phone. How many times has your phone 'crashed' in the last year - compare this to the phone of 30 years ago. Some systems are built to a much higher engineering tolerance (aircraft systems for example) - BA should have ensured it's core IT systems reached the same level of zero-failure tolerance.
Secondly, we're emerging into a world where the offline backup has been removed and so hence the white-board improvisation we saw recently from BA staff. A digital only world is inevitable, but is inevitably only a good thing if a zero-failure tolerance culture is created around it.
Until and unless corporate IT can learn these lessons, they need to keep the offline systems and processes switched on. The cost for not doing so, BA will likely be counting for some time to come.
One theory of my IT veteran is that when the power came back on, the systems were unusable because the data was unsynchronised. In other words the airline was suddenly faced with a mass of conflicting records of passengers, aircraft and baggage movements - all the complex logistics of modern air travel. He says: "This would have meant that BA would need to restore to a known synchronised back-up point (potentially days old), which brings in the previous argument about the hands-on skills required to achieve this." In summary, complex IT systems do fail from time to time, but smart organisations have the people and processes in place to recover quickly. BA has said little so far about what went wrong. However, it will now be under pressure from investors, staff and passengers to provide some answers.