During 8C-checks on NG we have several cases of chafed bellcranks on inboard aft flap actuating mechanism. Description and pictures below:
On the B-737 NG you can find damaged bellcranks on aft flap actuating mechanism in INBD main flap during internal visual inspection. Damage is caused by the aft flap actuating mechanism control cable fork. Repairing of bellcranks rests in damage removal with 1 inch radius blend ratio and with 63 um roughness, then you must measure remain of bellcrank material thickness, when is there found thickness less than 6,223mm you must report bellcrank to the Boeing. After measuring perform NDT with HFEC and do the flap peening on reworked area, then apply surface treatment. Against next chafing between fork and bellcrank you must insert teflon washers to the bellcrank.
Little tip to bellcranks removal – when you loose the control cable, count turn of turnbuckle and write down to the paper tape attached to the turnbuckle. When you install bellcranks back to the flap you can tight the turnbuckle by the same amount of turn and then only check the adjusting of aft flap actuating mechanism and cables tension. Thanks to Josef from Czech Republic.