HAL (Hindustan Aeronautics Limited) is a type of PSU.
It was established in the year 1940 as Hindustan Aircraft.
It’s headquarter is located in Bengaluru, Karnataka, India.
Its products are
Transport aircraft
Fighter aircraft
Helicopters

As you have asked about the HAL Management Trainee Call Letter, I want to tell you that it has not been released by HAL.
So you have to wait till the release of it to download it.

However you can check from its website, to know about it.

Firstly go to HAL website, the page open look like





Then click on Careers, the page open look like





Here you will find the details regarding the details of Call Letter of Management Trainee when available.