Fix incorrect indexing in max_acceleration_power_off_time

Co-authored-by: Gui-FernandesBR <63590233+Gui-FernandesBR@users.noreply.github.com>

Author: Copilot

rocketpy/simulation/flight.py

@@ -2863,7 +2863,7 @@ def max_acceleration_power_off_time(self):
         max_acceleration_time_index = np.argmax(
             self.acceleration[burn_out_time_index:, 1]
         )
-        return self.acceleration[max_acceleration_time_index, 0]
+        return self.acceleration[burn_out_time_index + max_acceleration_time_index, 0]
 
     @cached_property
     def max_acceleration_power_off(self):

tests/unit/simulation/test_flight.py

@@ -659,3 +659,35 @@ def test_stability_static_margins(
         assert np.all(moments / wind_sign <= 0)
     else:  # static_margin == 0
         assert np.all(np.abs(moments) <= 1e-10)
+
+
+def test_max_acceleration_power_off_time_with_controllers(
+    flight_calisto_air_brakes,
+):
+    """Test that max_acceleration_power_off_time returns a valid time when
+    controllers are present (e.g., air brakes). This is a regression test for
+    a bug where the time was always returned as 0.0.
+
+    Parameters
+    ----------
+    flight_calisto_air_brakes : rocketpy.Flight
+        Flight object with air brakes. See the conftest.py file for more info
+        regarding this pytest fixture.
+    """
+    test = flight_calisto_air_brakes
+    burn_out_time = test.rocket.motor.burn_out_time
+
+    # The max_acceleration_power_off_time should be at or after motor burn out
+    # It should NOT be 0.0, which was the bug behavior
+    assert test.max_acceleration_power_off_time > 0, (
+        "max_acceleration_power_off_time should not be zero"
+    )
+    assert test.max_acceleration_power_off_time >= burn_out_time - 0.01, (
+        f"max_acceleration_power_off_time ({test.max_acceleration_power_off_time}) "
+        f"should be at or after burn_out_time ({burn_out_time})"
+    )
+
+    # Also verify max_acceleration_power_off is positive
+    assert test.max_acceleration_power_off > 0, (
+        "max_acceleration_power_off should be greater than zero"
+    )