diff --git a/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/filter_check.py b/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/filter_check.py
index 1503433a..6d5db9d7 100644
--- a/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/filter_check.py
+++ b/csaxs_bec/bec_ipython_client/plugins/OMNY_shared/filter_check.py
@@ -9,12 +9,24 @@ def filters_out_of_beam(dev, tol: float = 0.1) -> tuple[bool, list[str]]:
     Reuses cSAXSFilterTransmission's own axis list/position table (index 0 of
     each row is the "out" position) so there is one source of truth for what
     "out" means, matching csaxs.fil_trans()/_fil_trans_report()'s own check.
+
+    Tolerates a deployment missing one or more filter axes (e.g. a simulated
+    session without the real beamline's filter_array_* devices), and `dev`
+    itself being None (the usual state of the module-level `dev =
+    builtins.__dict__.get("dev")` idiom used throughout this codebase before
+    a real BEC session has set it). BEC's device container raises
+    DeviceConfigError -- not AttributeError -- for a missing device, so a
+    plain `getattr(dev, axis_name, None)` does NOT safely skip it; wrapping
+    the lookup itself in try/except does, for both cases.
     """
     offending = []
     for axis_name, positions in zip(
         cSAXSFilterTransmission._AXES, cSAXSFilterTransmission._POSITIONS_USER
     ):
-        axis_obj = getattr(dev, axis_name, None)
+        try:
+            axis_obj = getattr(dev, axis_name, None)
+        except Exception:
+            axis_obj = None
         out_position = positions[0]
         if axis_obj is None or out_position is None:
             continue
diff --git a/tests/tests_bec_ipython_client/test_filter_check.py b/tests/tests_bec_ipython_client/test_filter_check.py
new file mode 100644
index 00000000..a45d6894
--- /dev/null
+++ b/tests/tests_bec_ipython_client/test_filter_check.py
@@ -0,0 +1,81 @@
+"""Tests for filters_out_of_beam() (csaxs_bec/bec_ipython_client/plugins/OMNY_shared/filter_check.py).
+
+Regression coverage for a bug surfaced on a simulated flomni session:
+tomo_scan_projection() -> filters_out_of_beam() crashed with
+DeviceConfigError: Device filter_array_1_x does not exist, because the sim
+config (unlike the real beamline's bl_endstation.yaml) doesn't define the
+filter_array_*_x devices at all. The lookup used `getattr(dev, axis_name,
+None)`, but BEC's device container raises DeviceConfigError (a plain
+Exception, not AttributeError) for a missing device, so getattr's default
+never applied.
+"""
+
+from unittest import mock
+
+from bec_lib.bec_errors import DeviceConfigError
+
+from csaxs_bec.bec_ipython_client.plugins.OMNY_shared.filter_check import filters_out_of_beam
+
+
+class _FakeDeviceContainer(dict):
+    """Stands in for BEC's real device-manager container: attribute access
+    for a present device returns it, for a missing one raises
+    DeviceConfigError (not AttributeError) -- see devicemanager.py's
+    __getattr__."""
+
+    def __getattr__(self, attr):
+        dev = self.get(attr)
+        if not dev:
+            raise DeviceConfigError(f"Device {attr} does not exist.")
+        return dev
+
+
+def _axis_at(position: float):
+    axis = mock.MagicMock()
+    axis.readback.get.return_value = position
+    return axis
+
+
+def test_filters_out_of_beam_dev_is_none():
+    # The usual state of the module-level `dev` idiom before a real BEC
+    # session has set it (`dev = builtins.__dict__.get("dev")`) -- several
+    # LamNI/Flomni call sites pass this straight through. Must not raise.
+    all_out, offending = filters_out_of_beam(None)
+
+    assert all_out is True
+    assert offending == []
+
+
+def test_filters_out_of_beam_all_devices_missing_from_container():
+    # Mirrors a simulated deployment: none of the filter_array_*_x devices
+    # exist at all. Must not raise, and must report "all out" (nothing to
+    # check -> vacuously true), matching the existing axis_obj-is-None skip.
+    dev = _FakeDeviceContainer()
+
+    all_out, offending = filters_out_of_beam(dev)
+
+    assert all_out is True
+    assert offending == []
+
+
+def test_filters_out_of_beam_some_devices_missing_from_container():
+    # A mixed deployment: filter_array_1_x exists and is out of the beam,
+    # the other three axes don't exist at all.
+    dev = _FakeDeviceContainer(filter_array_1_x=_axis_at(25.0))
+
+    all_out, offending = filters_out_of_beam(dev)
+
+    assert all_out is True
+    assert offending == []
+
+
+def test_filters_out_of_beam_flags_axis_in_beam():
+    dev = _FakeDeviceContainer(
+        filter_array_1_x=_axis_at(25.0),  # out
+        filter_array_2_x=_axis_at(17.6),  # NOT out (out position is 25.5)
+    )
+
+    all_out, offending = filters_out_of_beam(dev)
+
+    assert all_out is False
+    assert offending == ["filter_array_2_x"]