6 Definitions and assumptions
Procedure 1
Determining spares quantities to stock
a
depot for the one-year sparing
interval
1
Determine the number (N) of in-service specified circuit packs serviced
by the depot.
2 Determine the pack failure rate (F) for the specified circuit pack in the
Spares planning guide. (See Note 1 below.)
3 Determine turnaround time (T) in hours. (See Note 2 below.)
4
Calculate the NFT value by multiplying N x F x T.
5 Determine the number of spares required by using the NFT values in
Table 4.
Note
I:
Pack failure rates are expressed in terms of the number of
failures per million hours.
Note
2:
For a single depot or repair house service, turnaround
timeis
typically 10 working days or 240 hours. For a centralized depot
service, it is typically two days or 48 hours.
For example:
A single depot services 10,000 Peripheral Equipment Power Supply (PE _-
Pwr Sup) (AC-NT8DO6AA)
(DCNT6D41AB)
packs. From the failure
rates listed in Table 2, the failure rate for this pack is 1.84 failures per one
million hours. If the turnaround time for a single depot is 48 hours, then:
NFT=
10,000 x
1.84
x 48 = 0.8832
WWOO
From the
NIT
values in Table 1, the number of spares required for NFT
value 0.8832 = 6. See Table 1.
Spares planning 553-3001-l 53
s.