A Captain questions company Maintenance Control and Engineering's approval and use of speed tape to address missing and damaged rivets (fasteners) at the # 3 Middle Flap Fairing on two different B737-800 aircraft. The Pilot notes an Airworthiness Directive (AD) had been issued for the rivets; requiring Interim Repair or CDL deferral.

Narrative

Last two trips I have encountered the same damage to two different B737-800 aircraft. In one instance; 30 minutes before Flight Attendants (F/A's) went illegal; Maintenance Control got company Engineering approval to speed tape two missing; plus two damaged rivets on # 3 Flap Fairing; with a four-day deferral. In another instance; (after 5-hour delay); same company Engineering approved speed tape [application]. [Maintenance] did not have the heavy sheet metal required to overlap the three missing; plus one damaged rivets. Maintenance advised there is an FAA Airworthiness Directive (AD) issued for these five rivets located on the upper edge; outboard section of the # 3 Middle Flap Fairing. If any rivet is damaged; interim repair requires 1/8' inch sheet metal to overlap the damaged area and secured with screws or rivets. Maintenance Control initially was confused as to whether this item was a primary or secondary surface on aircraft. One or other cannot be speed taped. This fairing is one of the few that cannot be removed and flown without referencing a B-737 CDL [deferral]. I have my doubts as to whether the FAA really approves the speed tape and extended deferrals.