When the pilot at the flight controls of a helicopter engaged in an external-load operation is not verbally guided by a flight crew member on board the helicopter, or by a person the ground using two-way radio communication or the appropriate hand signals, and such pilot is not able to monitor the external load from his or her station, such helicopter shall be fitted with a mirror in such manner that such pilot is able to monitor the external-loan from his or her station and conduct the operation without such guidance.