There seems to be a lack of understanding of how company disciplinary procedures work in the UK. Most of them follow as a minimum the model code published by ACAS. This has been agreed by both sides of industry, and arguably does lean in favour of the employee.
From what I've read, the individual in this case was already subject to the company's disciplinary procedure, reportedly following two incidents within the space of a month in 2006 at BHX, including stripping down to his underwear to make a point (arguably that in itself would be grounds for a dismissal for gross misconduct, bringing the company into disrepute). As a result, he was subject to a final written warning (translate as "step out of line once more, and you are out").
The tribunal will therefore look at whether the previous disciplinary actions were "fair" (fair means were the allegations investigated fairly, with the individual concerned, etc). If so, was the subsequent cockpit incident also dealt with fairly ?
If the answer is yes to both, the company has no case to answer.
A final written warning is exactly what it says, and even the smallest aberration thereafter is grounds for "fair" instant dismissal.