The Department may, to such extent as it may deem reasonable, offer, in an advisory capacity, the engineering or other technical services and facilities of the Department, and such services and facilities as may be supplied to it by other Departments of the State, without charge, to any municipality or political subdivision desiring them in connection with the construction, maintenance or operation or proposed construction, maintenance, or operation of an airport or restricted landing area; provided, the Department may charge for such engineering or other technical services and facilities when payment for such services and facilities or reimbursement therefor is made by the United States Government, or any agency or Department thereof, and the payment or reimbursement therefor will not result in a decrease in the amount of money or funds otherwise payable by the United States Government to the municipality or political subdivision requesting such services and facilities; provided further that the Department shall not furnish to municipalities or political subdivisions the engineering services normally provided by consulting engineers to municipalities or political subdivisions.