An example of how the IRS imposed penalties on an estate for the decedent’s, and later the executor’s, failure to properly file the Forms 3520 and 3520-A.

The IRS requires certain U.S. persons to file informational returns to report
their relationships to, and transactions with, foreign trusts. Internal Revenue
Code § 7701(a)(30). This requirement also imposes the responsibility to file
such informational trust returns on the estates of some deceased U.S. persons.
Informational returns are just that, used to report certain information, but not
to directly impose taxes.
This article specifically explores the effects of these filing requirements on the executors of the estates of U.S. decedents, while also considering the effect of the open-ended Offshore Voluntary Disclosure Program (OVDP), offered by the IRS as an option to seek resolution of prior filing mistakes or omissions.

ABA Source Link: Foreign Trusts: Form 3520 and From 3520-A—Filing Deadlines and Liability of a Decedent’s Estate