47-42-19 DOUGLAS: (Was Service Note 5 of AD-781-1.) Applies to the Following DC-6 Aircraft: Serial Numbers 42854 to 42894, Inclusive; 43000 to 43012, Inclusive; 43055, 43056, and 43062. \n\nInspection required at every engine change. \n\nAfter the stop holes are drilled in the tail stub extension of the horizontal stabilizer front spar caps, as required by AD 47-42-11, inspect for signs of cracks, or progress of cracks, at each engine change period. If the aircraft has been modified to incorporate the elevator fifth hinge modification, the inspection period may be extended to every other engine change period, but not to exceed 3,000 hours of airplane operation. If cracks progress beyond the stop hole, operation of the airplane must be discontinued until additional corrective measures have been determined.