Is what the husband did permissible by dealing with another printing press to print the safety instructions for the aircraft without his manager's knowledge, and is the money resulting from that permissible? And is he sinful for accepting the private work outside official working hours, which later turned out to be related to his original company's work, and is this money permissible?

If the husband worked outside his original working hours, his earnings are permissible for him. However, issuing an invoice in the name of the printing press he works for, without its permission, is not permissible. Placing the profit back into the printing press does not absolve him of responsibility. He must return to the company, inform them of what happened, and return their right unless they absolve him. If he performed the work during his working hours, then it is not permissible for him, and the ruling on the earned money follows the ruling on the work itself. If the second agreement for the private work outside working hours was made with a company representative, without the husband knowing that the work would be issued in the name of the printing press he works for, then the default is that it is permissible, and he deserves the profit, and the representative alone bears the responsibility of paying the printing press its due.