B737-800
Situational Awareness; Communication Breakdown
Aircraft Equipment Problem Critical; Deviation / Discrepancy - Procedural Published Material / Policy
General Maintenance Action
Manuals; Procedure; Human Factors; Chart Or Publication; Aircraft; Company Policy
After release and delivery to the gate of a B737-800 aircraft from a C-Check; discussions took place as to whether the drain holes were installed in the Repair Doubler on the Right-Hand (R/H) Horizontal Stabilizer.  It was determined that the holes needed to be there and the aircraft be routed back to the Maintenance Base and inspected for drain holes.  Upon arrival at the gate; the inspection of the doubler revealed that the drain holes were not there.  The drain holes were located; drilled and treated at the gate.  The paperwork was signed-off (deferred item) and the aircraft was returned to service. There was an Engineering Authorization (EA) issued that provided deviations from the Structural Repair Manual (SRM) with the Aircraft Manufacturer's approval.  However; the EA did not address the drain holes; creating some confusion among those performing the task.  Once Engineering was asked about the holes; clarification was made.  Recommend following the paperwork more closely.
It was brought to my attention that information was submitted for a Right-Hand (R/H) Horizontal bottom repair doubler on a B737-800 aircraft that I was a part of.  Approximately four days earlier. I arrived at work and went to check on how the repair was doing.  I saw that everything was complete except for the two drain holes that where removed because of the doubler.  I did mention that the Structural Repair manual (SRM) reference 55-10-01 Repair XX did indicate to replace any drain holes that might be affected by the doubler.  I also mentioned that I thought after the doubler was shot on [riveted in place]; a center line from the existing drain holes on each side of the repair would be drawn across the doubler and equal measurements placed to mark the holes like the others.  That didn't happen.  I was asked by Maintenance Supervisor if I could do that now and I said 'Yes'.  I was getting what tooling I thought would be needed to accomplish the task when I was informed not to; being that the Engineering Authorization (E/A) didn't exactly mention the holes; I guess the thought was they may not be needed; as the E/A was deviating from the SRM repair cutout.
A Maintenance Inspector; Maintenance Supervisor; company Engineer and a Mechanic report drain holes were not drilled at a repair doubler on the lower surface of the Right-Hand Horizontal Stabilizer of a B737-800 aircraft prior to departure.