What condition triggers the TAIL ROTOR QUAD FAIL caution?

• A. One or both tail rotor cables has failed
• B. Tail rotor bearings jam
• C. Tail rotor hydraulic pump failure
• D. Tail rotor gearbox fault

Answer: (B)

Tail rotor quad fail is triggered by a condition where the tail rotor becomes mechanically seized or bound, such as a jammed tail rotor bearing. When the bearings jam, the tail rotor cannot turn freely, placing abnormal load on the drive system and causing mismatches in the tail rotor speed/position sensing across the system’s channels. The fault logic then flags a quad-fail tail rotor warning to alert the crew to a potentially catastrophic tail rotor condition that needs immediate attention.

Other issues like failed tail rotor cables, hydraulic pump problems, or gearbox faults can affect tail rotor performance, but they don’t produce the same simultaneous multi-channel fault signal that the quad-fail indication represents. A jammed bearing directly creates a mechanical obstruction and abnormal drive condition that the quad-fail logic specifically detects.