in the ascertainment of the validity and authenticity of the travel documents
of embarking passengers, and in the necessary steps to prevent the loss or
destruction of documents by passengers en route to their destinations.
[...]
3.55 Contracting States shall not fine operators in the event that arriving and
in-transit passengers are found to be improperly documented where the
operators can demonstrate that they have taken adequate precautions to
ensure that the passengers had complied with the documentary requirements
for entry into the receiving State.
Inadmissible Persons
[...]
3.57 Recommended Practice.- In the event that the precautions referred to
in 3.53 have been taken