It might seem like stagnation but we have made rapid advancements in other sectors (the mobile computing revolution being an example). About air travel, I think

It might seem like stagnation but we have made rapid advancements in other sectors (the mobile computing revolution being an example). About air travel, I think the evolution has been more about safety than anything else ever since (barring exception of concorde which tried to optimize for speed). The modern passenger jet is much safer than its 60s counterpart.