Page:CAB Accident Report, New York Airways Flight 600.pdf/7

 -7-

A compllatlon of the overhaul records for the 51x aft transmssmn assemblles Operated by New York Alrways, 1nd1cates that there were 17 unsched- uled removals prlor to the next prescrlbed overhaul tune. These occurred between July 27‘, 1962, and September 30, 1963. Wlth the exceptlon of the selected samples, no transm1581on assemblies operated to their scheduled EGO-hour or hOO-hour over- hauls mthout premature removal. In addltlon, only one of the three samples used reached the hOO-hour plateau wathout pI‘lOI' removal for repalr. Follomng the approval of the SOD-hour overhaul tune there were elght mstances of early removals of the 51x transmsszLons 1nvolved. Three of the elght occurred below 200 hours and one was between 200 and £00 hours of each TSO. The last reneed Operatlons Specl- flcatlons-Malntenance, whlch :anreased the overhaul mterval to 800 hours, was effectlve October 11, 1963.

Analysm

The :anestlgatlon revealed that the quill shaft which transmlts the drlve force from the nus: box to the aft transmlssmn had felled 1n fatigue. Based on the phy51cal ev1dence and the tests performed subsequent to the accldent, the Board concludes that thls fatlgue was prec1p1tated by a lack of lubrlcatlcn followlng blockage of the quill shaft's two lubrlcatlon gets by metal shav1ngs. The Board further concludes that the fatlgue fallures of the three stepped studs dld not con- trlbute to the qulll shaft fallure but rather were the result of fatlgue progres- smn 1n the shaft.

The tests performed on a qulll shaft w1th exaggerated conditions of one-half and one—quarter degree nasallgnment falled to produce Significant wear. Therefore, 1t 15 felt that a meallgnment condltlon, if such ex1sted in 3/1! TA 9—10, dld not sigmflcantly affect qulll shaft S/N TIL—102. However, durmg the subsequent opera.— tion at only 50 percent torque, w1th the lubrlcatlon Jets blocked, the fatigue cracks developed w1th1n 50 hours of Operatlon.

Slnce the flrst shav1ngs 1n mlx box S/N A 11—102 were found durlng the 1n1t1al load run, but prior to matlng at with aft transmsszmn S/N TA 9-10, 1t follows that shav1mgs were 1ntroduced unto the lubrlcatlon system as a result of the lnltlal borlng Operation by the manufacturer. It 15 passable that addltlonal shavlngs may have be 3.11troduced darmg subscquent borlng operatlons on author the aft transmissmn or IIL'L'XZ box. It 15 Slgnlflcant that followlrg ohscovery of the plugged lubrlcatlon gets two changes were moorporated 1n the manufacture and overhaul of transmsszmn assemblles. Plastlc plugs were 1nserted 1n the 011 pas- sages durnng the borlng Operation on the llners, and all plug type lubricatlon Jets were removed przLor to the flushlng of casas durmg overhaul. These changes were accompllshed to reduce the p0551b111ty of metal shamngs becomng lodged 1n the narrow passages of the case, or an the orlflces of the 3ets durlng the borlng or flushing procedure.

The Board belleves that the number of premature removals of aft transmisszLons was excass:.ve. a rev1ew of the overhaul records of sampled and unsampled assem— blles reflects that an morease beyond a hOO-hour TSO, mthout addltlonal operatmg experlence, was unwarranted. It 15 acknowledged that the sprag clutch fallures and exce531ve wear of bearlng l1ners, whlch 1n the Board's oplnlon presented a tune— related correlation, were remedled. However, the operatlng experlence of the aft transmssions in general did not present a satlsfactory performance record. Only one of the 51x assemblles reached 1ts 1n1t1ally scheduled too—hour overhaul mthout premature removal. Followzmg the lacrosse 1n overhaul tune to 600 hours, there