Following maintenance, a clevis pin came out of the RP-4 roll trim system pulley on a QuikR causing a left turn. The split ring securing the clevis pin had come out. It is not known if the ring was disturbed during the maintenance.
The split ring which came out was the same “spiral start” pattern as that which has caused trouble before (see Service Bulletin 139). This pattern of ring has no positive stop, so that simple rotation of the ring (e.g. caused by it getting caught on something) will cause it to disengage. See A below, showing the ring starting to disengage.
Type C is better having a 90 degree positive stop. Type D is used on the QuikR and GTR washout rod universal joints and the most secure type of ring, having no starting ramps and 2 complete turns through the hole. All type A split rings have been discarded at the Factory.
Split rings of the spiral start pattern “A” above must be removed in all locations and be replaced with stainless steel split pins or rings to pattern C or D. The small 4mm clevis pins used in the RP-4 pulley take a 1/16” split pin, part no. FPSP-002. Larger clevis pins take 5/64” stainless steel 316 split pins, part no. FPSP-005.
The ends of the split pin should be trimmed and curled over so as to minimise the possibility of snagging.
The aircraft technical log must be signed “ Service bulletin SB144 (split rings) carried out” by a qualified inspector and/or an owner/operator.
4) Continued Airworthiness
At each permit revalidation, the inspector must check the service bulletin has been carried out, that there are no split rings of the “spiral