In paragraph 4 (lines 55-74), the authors mention that it m...

it should take into account the different amounts of work or the psychological stress undergone by L2 pilots and controllers in their real life environment.

it does not cover as many language skills and proficiency levels as necessary to validate pilots and controllers’ performance in the L2.

it does not consider the ICAO’s language proficiency requirements for aviation professionals.

the number of air traffic controllers and pilots who need to be tested is very large.

the proficiency levels of the high L2 and low L2 groups are very different.