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lk 0 L . * .son GAS TURBINE DIVISION

TURBINE ASSEMBLY - SECOND -STAGE NOZZLE--REWORK

1. PLANNING INFORMATION:

A. Effectivity:Model 250-C20 and 817 engines incorporating P/N 6878426 Second-stageTurbine Nozz les at time of conversion to 250-C2OB or B17B. (ReferenceC20 CEB-1053 or B17 TP CEB-10531

B. Reason:To rework the OD of current production, new material 250-C20 and 517second-stage turbine nozzles to the 250-C20B and B17B configuration totransfer balance air from within the gas producer support to the powerturbine support. New features of current production second-stagenozzles include:(1) Material changed from X-40 to IN-738 to improve high temperature

strength and stabil ity.(21 Added stiffening ring to increase interstage seal stiffness,

thereby improving seal concent ricity.(31 Redirected first-stage cooling air.

C. Description:The second-stage turbine nozzle is reworked by grinding or machining abalance air annulus in the nozzle OD. The balance air annulustransfers high pressure air from within the gas producer support to thepower trubine support upper right and right struts. The externalbalance air tubes, which transfer high pressure air between the 250-C20and B17 gas producer and power turbine supports, were eliminated in thenew 250-C2OB and B17B supports.Also , the relief between the nozzle second-stage wheel shroud OD andnozzle tang is removed by grinding or machining the relief flush to theadjacent surfaces. Following rework, the nozzle is reidentified.

July 1, 1984Revision No. 2February 15, 1988

250-C20 CEB-1054250-817 TP CEB-1054

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ALLISON GAS TURBINECommercial Engine Bulletin

1. PLANNING INFORMATION: (Continued)

F. Interchangeability:Al l changes described in this bu lletin must be accomplishedsimultaneously.

G. Compliance:To be accomplished concurrently with 250-C20 CEB-1053 or 817 TP CEB-1053

I H. Approval: Technical aspects are FAA approved.I. Material Ava ilabili ty: None.

J. Tooling: None.

K. Weight and Balance: Not Affected

I L. Reference: 250-C20 CEB-1053, 250-817 TP CEB-1053, ATW 2060

July 1, 1984Revision No. 2February 15, 1988

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ALLISON GAS TURBINECommercial Engine Bulletin

2. ACCOMPLISHMENT INSTRUCTIONS:

A. Al l P/N 6878426 Second-stage Turbine Nozz les must pass overhaulinspection as described in the 250-C20 or 817 Overh,aul Manual prior torework.(1) Rework P/N 6878426 Second-stage Turbine Nozz les as follows:

(a) Remove the relief between the OD of the nozzle second-stagewheel shroud and nozzle tang by grinding or machining the6.&?10-6.780 relief OD flush with the 6.640 + 0.010 shroud ODand surface N. (See Figure 1.) Maintain drO30 radius andbreak sharp edge 0.010 UOS. Finish reworked surfaces 12w

(b) Grind or machine 0.150+ 0.010 wide balance air annulus fromsurface N (Figure 1) to the depth established by 7.012+0.010diameter. Add 0.030 radius (8 tang locations) and brezk sharpedges 0.010 UOS. Finish reworked surfacesU25 J'

(cl Reidentify reworked nozzles as follows:1 Obliterate the existing P/N 6878426.2 Reidentify as P/N 6878498 per AS478CL-G or AS478-2D l or 2E.-

I8. Record compliance with 250-C20 CEB-1054 or 817 TP CEB-1054 Revis ion

No. 2, in the Turbine Assembly (pink pages), Modification Record, PartIII of the Engine Log Book.

July 1, 1984Revision No. 2February 15, 1988

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ALLISON GAS TURBINECommercial Engine Bulletin

I

SURFACE N I

REMOVE DOTTEDAREAS

\ :xhv APPLY P/N 6878498 ; IERE PERAS478CL-G OR AS478-2D l OR 2E

REF6.8106.780DIAREF

ISECOND-STAGEWHEELSHROUD

IFIRST-STAGEWHEELSHROUD

AXIS AE-AE ESTABLISHED BY TANG PATTERN AND SURFACE NALLFEATURESSHALLBE CONCENTRICANDSQUAREABOUTAXIS AI-AE WITHIN FIR SPECIFIE D

AE c -_ AE

Second-Stage Turbine Nozzle OD ReworkFigure 1

July 1, 1984 250-C20 CEB-1054Revision No. 2 250-B17 TP CEB-1054February 15, 1988 Page 4

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ALLISON GAS TURBINECommenial Engine Bullet in

3. MATERIAL INFORMATION:

A. Basis for quantities is per turbine assembly.

B. Bil l of material:CZOB/B17B CZO/B17 Instructions/

P/N QW Nomenclature P/N Qty Disposition- -6878490 1 Nozzle Assy, 6878426 i 1

INSTRUCTIONS/DISPOSITION MOTES:1. Rework and reidentify.

July 1, 1984Revision No. 2February 15, 1988

PRODUCT SUPPORT

Allison Engine Company

250-C20 CEB-1054250-817 TP CEB-1054Page 5

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