SFECU Initiated Built in Test (IBIT) description
Effectivity: Global 7500 aircraft
ATA 27
The Global 7500 aircraft’s Wing High Lift System (WHLS) includes an Initiated Built in Test (IBIT) that runs once every two (2) days at power up. If the IBIT test is interrupted by a command from the Slat Flap Control Lever (SFCL), the test is not considered completed and will run again at the next power up. The IBIT can be manually initiated from the onboard maintenance system (OMS) during ground maintenance.
Failures, if detected, are isolated to a faulty Line Replaceable Unit (LRU) and an associated message will be displayed on the OMS.
The IBIT includes the following tests:
(1) Regen resistor test
(2) Inverter switch test
(3) Motor Brake tests
(4) Asymmetry Brake tests
Test (1-2): During the IBIT, the regen resistor and the inverter switch tests are run prior to enabling the motor for the Motor Brake test (3) and Asymmetry brake test (4). A failure of the regen resistor or inverter will result in the loss of the channel being tested. When a regen resistor or inverter failure is detected during the IBIT tests, the SFECU channel is shutdown to prevent the failed part from causing more damage to the other SFECU components. The SFECU regen resistor is used to dump the excess of electric energy by transforming that energy into heat when the SFECU motor goes into generator mode (Regenerative energy dissipation).
Test (3): The motor brake test eliminates dormant motor brake failures. The motor brake test is performed by commanding current into the motor without releasing the motor brake. Motor brake test pass/fail criteria is based on the motor speed change. If a SFCS channel detects a motor brake failed in a released state, the corresponding opposite channel is also disabled to force a FAIL EICAS message rather than a HALFSPEED message. The channel under test communicates the status of this test on the cross-channel bus.
Test (4): The asymmetry brake test is used to verify the holding torque of the wingtip brakes. When this test runs, the PDU gradually increases the torque to the wingtip brake under test while the brake is engaged, and brake torque switch (BTS) closure indicates a minimum brake capacity. If the brake slips excessively during this test, the BTS will not close, and IBIT will not pass.