Section 35(1)(i) in National Housing Bank (Officers') Service Regulations, 1997
(i)An officer in junior Management Grade may travel by 1st class or AC Sleeper by train. He may, however travel by air (economy class) if the distance to be travelled is more than 500 kms. He may, however, travels air (economy class) even for a shorter distance if so permitted by the Competent Authority, having regard to the exigencies business or public interest.