He is being humourous. By 'coming down faster than they go up', he means 'crashing'! And compared to his (the writer's) mangled body, pity the poor airline: the mangled body of what's left of their multi-million dollar plane is now next to nothing.
(Old planes are sold off to smaller airlines, not traded-in, but he is being humourous and treating the situation akin to trading in an old car. Usually, the car is in some working order - we don't walk into a car dealership with a bumper bar and steering wheel tucked under our arm and talk about a trade-in on a new car! He gives us the humourous image of the airline asking Boeing for a trade-in quote on the bits and pieces of the plane now scattered over the countryside.
In effect, it is a humourous attempt at minimizing personal anxiety and 'fear of flying'. He is saying that any anxiety a passenger might have is small - just the loss of their life - compared to how many millions the poor airline will lose if it loses its plane!
Student or Learner