VOLUME 3 GENERAL TECHNICAL ADMINISTRATION
CHAPTER 16 PRORATED TIME AUTHORIZATIONS
Section 1 Safety Assurance System: Determining the Prorated Time for an Item
3-616 REPORTING SYSTEM(S).
A. Program Tracking and Reporting Subsystem(s) (PTRS). Activity codes: 3316 and 5316.
B. Safety Assurance System (SAS). Use SAS automation and the associated Data Collection Tools (DCT).
3-617 OBJECTIVE. This chapter provides guidance in determining the prorated time for an item.
A. Definition of Proration. Proration is a procedure to determine
the time consumed under one maintenance system, and to establish the remaining time under a new system.
B. How Proration is Used. Certificate holders often sell or lease their
equipment to other certificate holders. This “used” equipment will have accumulated
a certain amount of time in service. This time is transferred to the new certificate
holder and may be phased in or prorated to the new certificate holder’s approved time limitations.
C. Buyer Options for Prorated Time. When a buyer’s approved overhaul
time limits are lower than those of the seller, the buyer has two options:
1) Elect to use the proration process.
2) Elect to use direct inclusion, providing the previous certificate holder’s actual
time since overhaul (TSO) is less than the buyer’s approved overhaul time limit.
a) When using the direct inclusion option, the difference between the buyer’s approved
overhaul time limit and the previous certificate holder’s actual TSO will determine
the time remaining to the overhaul for the buyer.
b) When the buyer’s approved overhaul time limit is higher than that of
the seller, proration procedures should be used to adjust the TSO. However,
based upon the buyer’s assigned principal maintenance inspector’s (PMI) comparison
of the buyer’s and seller’s maintenance programs for similarity, direct inclusion may be used if both programs are found comparable.
D. Scope and Limitations of Proration.
1) Proration does not lessen a certificate holder’s responsibility to maintain
the aircraft in an Airworthy condition.
2) Proration is optional.
3) Life-limited components may not be prorated.
4) Proration may not be applied to times specified in Airworthiness Directives (AD).
5) Certificate holders who have been operating equipment under Title 14 of the Code of Federal Regulations (14 CFR) parts
6) Both adjusted and actual times must be shown on the proration document and the aircraft records.
7) When an item is inspected or overhauled as appropriate, the applicable prorated
time limits will be canceled. Thereafter, the item will be handled according to the certificate holder’s approved program.
8) Partial proration is not acceptable. A certificate holder
electing proration must prorate the airframe and all of its installed powerplants,
propellers, and appliances. Spare engines and propellers acquired at the time of sale or at a later date with “time in
service” may be prorated.
9) If an increase in a time limitation is approved for a certificate holder operating
on prorated times, that increase will be credited to the prorated item(s).
10) Amendments to a certificate holder’s operations specifications (OpSpecs) that
increase time limits apply to all aircraft of the same type and model operated
by a carrier. Such time increases apply to aircraft operating on a prorated time basis, as well as to the other aircraft in the fleet.
E. Phasing in Foreign Aircraft with U.S. Type Certificates (TC). Foreign
air carrier aircraft for which there is a U.S. TC may be phased into a U.S.
air carrier’s program via proration. However, the U.S. certificate holder must
first present satisfactory evidence that the program under which the aircraft
was maintained is at least equivalent to the new certificate holder’s program for a similar type of aircraft.
3-619 DATA AND COMPUTATION.
A. Computing Prorated Time. Prorated time remaining can be determined by using the following mathematical procedures:
1) Divide the actual time used by the previous certificate holder’s approved time
limit under which the aircraft has been operated. The result, carried to two
decimal places, will represent the percentage of approved time already used.
2) Multiply the new certificate holder’s time limit by the percentage of
time used. This will result in the prorated time to be used under the new program.
3) Subtract the prorated time from the time limit approved in
the new program. The result will represent the number of hours remaining under the new program. (See Figure 3-66, Proration Formula Example.)
B. Block/Pattern Time Limitation.
1) When block/pattern time is to be prorated, each block/pattern
shall be treated as though a complete aircraft were being prorated.
2) When the previous certificate holder used a block/pattern system, a document must be submitted showing the following:
· Time limitation for each block or pattern, together with a
list of items that are part of the block or pattern; and
· Time since accomplishment for each individual item on the
3-620 COORDINATION REQUIREMENTS. This task requires coordination between the
inspector and the certificate holder.
3-621 REFERENCES, FORMS, AND JOB AIDS.
A. References (current editions):
· Advisory Circular (AC)
Control by Reliability Methods.
· Certificate holder’s documentation,
including OpSpecs, for previous and new certificate holder.
· Volume 3, Chapter 18, Section 6, Parts
D and E Maintenance OpSpecs/MSpecs/LOAs.
· Volume 10, Safety Assurance System Policy and Procedures.
B. Forms. None.
C. Job Aids. Figure 3-66.
A. Receive Data From Applicant. The certificate holder must submit required
information to the district office in which the certificate holder’s principal base of operation is located.
1) The certificate holder must submit all OpSpecs containing the time limits utilized
for the particular aircraft by the previous certificate holder.
a) If the OpSpecs do not show hours, the certificate holder must submit
other documentation that will establish the time limits.
b) If conversion to hours is necessary, the computations used for the conversion should be included.
2) The certificate holder must provide OpSpecs pertinent to the particular aircraft.
3) The certificate holder must submit documents itemizing the following:
· Engines, propellers, and appliances that have different
time limitations than the previous certificate holder and are to be prorated. These will be listed
by Airlines for America (A4A) chapter numbering system, showing the name, part number, serial number, and position;
· The approved time under which the aircraft has been
· The actual time since last accomplishment;
· The percent of time used by the previous certificate holder;
· The approved time limitation for the new certificate holder.
4) When the previous certificate holder used a block/pattern system, a document must be submitted showing the following:
· Time limitation for each block or pattern, together with a list
of items that are part of the block or pattern; and
· Time since accomplishment for each individual item on the aircraft.
B. Determine Eligibility. Determine that the aircraft and/or components are eligible for proration.
C. Check the Prorated Time Computation. Times obtained via proration
may be rounded to the nearest 10-hour figure. (See Figure 3-66.)
3-623 TASK OUTCOMES.
A. Complete the PTRS Record. For 14 CFR part
the required PTRS record. For
parts 121 and
SAS guidance Modules 4 and 5 for data collection and reporting.
B. Complete the Task. Successful completion of this task will
result in continuation of the certification task in accordance with the appropriate certification process.
C. Document the Task. File all supporting paperwork in the applicant’s office file.
3-624 FUTURE ACTIVITIES. Normal surveillance.
Figure 3-66. Proration Formula Example
The example below demonstrates the simple steps involved in determining a buyer’s time remaining to overhaul.
Previous certificate holder’s approved overhaul time limit = 8,000 hours
Previous certificate holder’s time since overhaul (TSO) = 2,000 hours
Buyer’s approved overhaul time limit = 12,000 hours
Divide the previous certificate holder’s TSO figure by the previous certificate
holder’s approved overhaul time limit. Carry this out to two places. The result represents the percentage of approved overhaul time already used.
2,000 ÷ 8,000 = .25
In this example, 25 percent is the result.
Multiply the buyer’s approved
overhaul time limit figure by the decimal arrived at in Step One. The result is the prorated TSO to be used by the buyer.
12,000 x .25 = 3,000
In this example, 3,000 is the prorated TSO to be used by the buyer.
Subtract the prorated TSO arrived
at in Step Two from the buyer’s approved overhaul time limit. The resulting figure will be the number of hours remaining to overhaul for the buyer.
12,000 - 3,000 = 9,000
In this example, the buyer’s prorated time remaining to overhaul is 9,000 hours.
RESERVED. Paragraphs 3-625 through 3-640.