Answer: Structural unemployment
Step-by-step explanation:
A middle-aged aircraft mechanic is laid off from his job after improved technology (robotics and machine learning) reduces the need for workers. This type of Structural unemployment.
Structural unemployment is an unemployment that occurs when the workers doesn't have the necessary skills which are required for the job and this occurs when there's improvement in technology or when the economy undergoes changes. In this case, their skills become obsolete.