The rule for whistle failure when the lead whistle unit is unavailable is found under which USOR section?

• A. USOR 413
• B. USOR 416
• C. USOR 410
• D. USOR 408

Answer: (C)

The situation tests knowing where whistle-failure procedures are located when the lead unit’s horn can’t be used. USOR 410 is the section that specifically covers whistle signals and whistle-failure scenarios, including what to do when the lead whistle unit is unavailable. It lays out the required actions to maintain proper audible warning by using the remaining units or following the prescribed alternative signaling method, so that crossing protection and crew safety are preserved. That direct focus on whistle failures with the lead unit out of service is why this is the best answer. The other sections deal with different whistle-related requirements and do not address the lead-unit-unavailable situation.