Page190 of 544 Sparesplanning
553-3011-100 Standard14.00 January 2002
F — The failure rate of a particular spares item.
T — The turnaround time for repairing a failed spares item in hours.
The formula will produce an NFT value. The number of spares required for a
one year period may be found by looking up the NFT value in the table
provided in this section.
The following procedure is an example of spares planning for the
NT8D14AA Universal Trunk Card.
Determining spares quantities for a one year sparing interv al
1Determine the number (N) of the particular item that is being serviced by
the depot.
For example, a single depot services 10,000 Universal Trunk Cards.
2Determine the failure rate (F) for the specified item.
From the Failure rates listed in Table58 on page 191, the failure rate for
the Universal Trunk Card is 3.4.
3Determine the turnaround time (T) in hours.
Assume a centralized depot with a turnaround time of 48 hours.
4Calculate the NFT value by multiplying N x F x T.
NFT = (10,000 units x 3.4 failures x 48 hrs) / 1,000,000 hrs = 1.632
From the NFT values in Table59 on page 193, the number of spares
required for NFT value 1.632 = 8.
That is, eight NT8D14AA Universal Trunk Cards are needed to last an
interval of one year when servicing 10, 000 Universal Trunk Cards.