Have the airlines ordered too many expensive new aircraft based on a belief that the additional capital costs of new aircraft would be more than offset by greater fuel efficiency?

The price of crude oil and jet fuel as priced in US $ has almost halved since the high levels of 2013 and 2014.

The first task is to explain the effects that this is currently having on the airline industry.

How are the airlines reacting?

What adjustments, if any, are they making to their strategies?

The second task is to consider the size and composition of the backlog of orders for the new aircraft. Have the airlines ordered too many expensive new aircraft based on a belief that the additional capital costs of new aircraft would be more than offset by greater fuel efficiency?