What is the fine-grained topic of the following text: We have the most modern fleet in the country to continue on this course”, mentioned Juan Carlos Zuazua, General Director of Viva Aerobus, who pointed out that Viva is the Mexican airline that have canceled the least national routes in the last two years, achieving a network stability of 92%. Only return the topic.
Viva Aerobus' modern fleet and stable national route network