STEP II 12,000 --- Buyer's approved O.H. time limit.
x .437 ------
84.000
360.00 4800.0 -------- 5244.000 --- Prorated TSO for buyer's block/pattern D
STEP III 12,000 --- Buyer's approved O.H. time limit.
- 5,244 ------- 6,756 --- Prorated time remaining to overhaul for buyer's block/pattern D.
It should be recognized that when an operator elects to transfer an aircraft from a block/pattern system to a one-time overhaul, a substantial amount of "time remaining to overhaul" must be sacrificed.
In the example given here, the buyer's "time remaining to overhaul" for each block/pattern is as follows:
A - 9756 C - 3756 B - 756 D - 6756 Since the buyer's approved overhaul time is 12,000 hours, it follows that all the items in block/pattern "B" will be due for overhaul within 756 hours. To phase the aircraft into a onetime overhaul, all blocks would have to be overhauled at this time.
---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 2. TRANSFER OF AIRCRAFT FROM A BLOCK/PATTERN SYSTEM TO A
BLOCK/PATTERN SYSTEM In this type of situation, each block/pattern is prorated as though it was the overhaul time for the entire aircraft.
KNOWN (Based on the figures established in Figure 1.)
16,000 hours --- Previous operator's approved time limit which is divided into four blocks/patterns of 4,000 hours each.
.187 --- Percent of block/pattern A overhaul time used by previous operator.
.937 --- Percent of block/pattern B overhaul time used by previous operator.
.687 --- Percent of block/pattern C overhaul time used by previous operator.
.437 --- Percent of block/pattern D overhaul time used by previous operator.
12,000 hours --- Buyer's approved overhaul time limit which is to be divided into four blocks/patterns of 3,000 hours each. (Blocks/patterns I, II, III, and IV) COMPUTATION BLOCK/PATTERN NO. I STEP I 12,000 --- Buyer's approved overhaul time limit.
x .187 --- Percent of overhaul time used by previous ------ operator.
84.000
960.00 1200.0 -------- 2244.000 --- Prorated TSO for buyer's block/pattern No. I.
STEP II 12,000 --- Buyer's approved overhaul time limit.
-2,244 ------ 9,756 --- Prorated time remaining to overhaul for buyer's block/pattern No. I.
COMPUTATION BLOCK/PATTERN NO. II STEP I 12,000 X .937 ------
84.000
360.00
10,800.0 ---------- 11,244.000 --- Prorated TSO for buyer's block/pattern No. II.
STEP II 12,000 -11,244 ------- 756 --- Prorated time remaining to overhaul for buyer's block/pattern No. II.
COMPUTATION BLOCK/PATTERN NO. III STEP I 12,000 x .687 ------
84.000
960.00 7,200.0 --------- 8,244.000 --- Prorated TSO for buyer's block/pattern No. III.
STEP II 12,000 -8,244 ------ 3,756 --- Prorated time remaining to overhaul for buyer's block/pattern No. III.
COMPUTATION BLOCK/PATTERN NO. IV STEP I 12,000 x .437 ------
84.000
360.00 4,800.0 --------- 5,244.000 --- Prorated TSO for buyer's block/pattern No. IV.
STEP II 12,000 -5,244 ------
6,756 --- Prorated time remaining to overhaul for buyer's block/pattern No. IV.
---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 3. TRANSFER OF AIRCRAFT FROM A ONE-TIME OVERHAUL TO A
BLOCK/PATTERN SYSTEM (BUYER'S APPROVED OVERHAUL TIME
LIMIT IS HIGHER THAN THAT OF THE PREVIOUS OPERATOR) In this process it is first necessary to find the buyer's "prorated time since overhaul" and his prorated "time remaining to overhaul" for the entire aircraft. This is accomplished by first applying the routine proration formula as shown below.
KNOWN 12,000 hours --- Previous operator's approved overhaul time limit.
3,000 hours --- Previous operator's time since overhaul.
16,000 hours --- Buyer's approved overhaul time limit which is to be divided into four blocks/patterns of 4,000 hours each. (Blocks/patterns A, B, C, and D) STEP I _____.250 --- Percent of overhaul time used by 12,000/3,000.000 previous operator.
STEP II 16,000 --- Buyer's approved overhaul time limit.
x .250 ------
800.000 3,200.0 --------- 4,000.000 --- Buyer's prorated TSO.
STEP III 16,000 --- Buyer's approved overhaul time limit.
-4,000 --- Buyer's prorated TSO.
------ 12,000 --- Buyer's prorated time remaining to overhaul.
In this particular example, since the buyer has elected to transfer an aircraft from a one-time overhaul to a four block/pattern system, he should recognize that a substantial amount of his time remaining to overhaul will have to be
sacrificed. This is brought about by the need to overhaul the entire aircraft prior to 12,000 hours and at the same time, phase selected portions of it into various blocks/patterns.
EXAMPLE The buyer, desiring to establish a four block/pattern system, separates his maintenance program into four equal parts and places the items so separated into either block/pattern A, B, C, or D. Assuming the selection has been made, the blocks/patterns would look like this:
Block/pattern A = 4,000 hours (cumulative time = 4,000 hours) Block/pattern B = 4,000 hours (cumulative time = 8,000 hours) Block/pattern C = 4,000 hours (cumulative time = 12,000 hours) Block/pattern D = 4,000 hours (cumulative time = 16,000 hours) The effect on items in each block/pattern as the result of phasing them into a four block/pattern system would be as follows:
BLOCK/PATTERN A These items would have to be overhauled at 4,000 hours TSO for the buyer.
This would result in a loss of 8,000 hours "time remaining to overhaul."
BLOCK/PATTERN B These items would have to be overhauled at 8,000 hours TSO for the buyer.
This would result in a loss of 4,000 hours "time remaining to overhaul."
BLOCK/PATTERN C These items will be overhauled at 12,000 hours TSO for the buyer.
Since it was previously established through proration that this was the buyer's "time remaining to overhaul," no time will be sacrificed on the items scheduled in this block/pattern.
BLOCK/PATTERN D The items in this block/pattern will have to be overhauled at a point at, or prior to 12,000 hours and again at 16,000 hours in
order to properly phase them into the system. The initial time of overhaul of these particular items should be at the option of the buyer, providing they do not exceed 12,000 hours. There are several methods he may choose from to accomplish this initial overhaul. Among these are:
1. Initially O.H. all block/pattern D items in block/pattern A
2. Initially O.H. all block/pattern D items in block/pattern B
3. Initially O.H. all block/pattern D items in block/pattern C
4. Initially O.H. 1/2 of all block/pattern D items in block/pattern A and O.H. 1/2 of all block/pattern D items in block/pattern B
5. Initially O.H. 1/2 of all block/pattern D items in block/pattern B and O.H. 1/2 of all block/pattern D items in block/pattern C
6. Initially O.H. 1/2 of all block/pattern D items in block/pattern A and O.H. 1/2 of all block/pattern D items in block/pattern C
7. Initially O.H. 1/3 of all block/pattern D items in block/pattern A and O.H. 1/3 of all block/pattern D items in block/pattern B and O.H. 1/3 of all block/pattern D items in block/pattern C Because of the previously established prorated figure of 12,000 hours remaining to overhaul, the buyer stands to lose the same total amount of time regardless of which method he chooses.
Method #7 appears to be the most practical approach, since it would tend to spread the workload over a 12,000 hour period. The entire block/pattern D would, of necessity, have to be overhauled again at 16,000 hours at which time all items would be correctly phased into their proper block/pattern. Consideration should be given by the assigned inspectors to the extent of inspection (overhaul) required in the case of initial overhauls that are accomplished early solely for the purpose of phasing an aircraft into a block/pattern system.
In the foregoing example, it can readily be seen that block A items at the time of initial overhaul by the buyer will actually have accumulated only 7,000 hours since previously overhauled while block/pattern C items will have accumulated 15,000 hours.
In either case, it must be remembered that another 16,000 hours will pass before they are overhauled again.
---------------------------------------------------------------- ----------------------------------------------------------------
FIGURE 4. TRANSFER OF AIRCRAFT FROM A ONE-TIME OVERHAUL TO A
BLOCK/PATTERN SYSTEM (BUYER'S APPROVED OVERHAUL TIME LIMIT IS LOWER THAN THAT OF THE PREVIOUS OPERATOR.)
In this process it is first necessary to find the buyer's prorated "time since overhaul" and prorated "time remaining to overhaul" for the entire aircraft. This is accomplished by first applying the routine proration formula as shown below:
KNOWN 12,000 hours --- Previous operator's approved overhaul time limit.
3,000 hours --- Previous operator's time since overhaul.
8,000 hours --- Buyer's approved overhaul time limit which is to be divided into four blocks/patterns of 2,000 hours each (A, B, C, and D).
STEP I _____.250 --- Percent overhaul time used by 12,000/3,000.000 previous operator.
STEP II 8,000 --- Buyer's approved overhaul time limit.
x.250 -----
400.000 1,600.0 --------- 2,000.000 --- Buyer's prorated TSO.
STEP III 8,000 --- Buyer's approved overhaul time limit.
-2,000 --- Buyer's prorated TSO.
------ 6,000 --- Buyer's prorated time remaining to overhaul.
In this particular example, since the buyer has elected to transfer an aircraft from a one-time overhaul to a four block/pattern system, he should recognize that a substantial amount of his time remaining to overhaul will have to be sacrificed. This is brought about by the need to overhaul the entire aircraft prior to the accumulation of 6,000 additional hours and at the same time, phase selected portions of it into various blocks/patterns.
EXAMPLE The buyer, desiring to establish a four block/pattern system, separates his maintenance program into four equal parts and places the item so separated into either block/pattern A, B, C, or D. Assuming the selection has been made, the block/pattern would look like this:
Block/pattern A = 2,000 hours (cumulative time = 2,000 hours) Block/pattern B = 2,000 hours (cumulative time = 4,000 hours) Block/pattern C = 2,000 hours (cumulative time = 6,000 hours) Block/pattern D = 2,000 hours (cumulative time = 8,000 hours) The effect of items in each block/pattern as the result of phasing them into a four block/pattern system would be as follows:
BLOCK/PATTERN A These items would have to be overhauled at 2,000 hours TSO for the buyer.
This would result in a loss of 4,000 hours "time remaining to overhaul."
BLOCK/PATTERN B These items would have to be overhauled at 4,000 hours TSO for the buyer.
This would result in a loss of 2,000 hours "time remaining to overhaul."
BLOCK/PATTERN C These items will be overhauled at 6,000 hours TSO for the buyer.
Since it was previously established through proration that this was the buyer's "time remaining to overhaul," no time will be sacrificed on the items scheduled in this block/pattern.
BLOCK/PATTERN D The items in this block/pattern will have to be overhauled at a point at, or prior to 6,000 hours and again at 8,000 hours in order to properly phase them into the system. The initial time of overhaul of these particular items should be at the option of the buyer, providing they do not exceed 6,000 hours. There are several methods he may choose from to accomplish this initial
overhaul. Among these are:
1. Initially O.H. all block/pattern D items in block/pattern A
2. Initially O.H. all block/pattern D items in block/pattern B
3. Initially O.H. all block/pattern D items in block/pattern C
4. Initially O.H. 1/2 of all block/pattern D items in block/pattern and O.H. 1/2 of all block/pattern D items A in block/pattern B
5. Initially O.H. 1/2 of all block/pattern D items in block/pattern and O.H. 1/2 of all block/pattern D items B in block/pattern C
6. Initially O.H. 1/2 of all block/pattern D items in block/pattern and O.H. 1/2 of all block/pattern D items A in block/pattern C
7. Initially O.H. 1/3 of all block/pattern D items in block/pattern and O.H. 1/3 of all block/pattern D items A in block/pattern and O.H. 1/3 of all block/pattern D items B in block/pattern C Because of the previously established prorated figure of 6,000 hours remaining to overhaul, the buyer stands to lose the same total amount of time regardless of which method he chooses.
Method #7 appears to be the most practical approach, since it would tend to spread the workload over a 6,000 hour period. The entire block/pattern D would, of necessity, have to be overhauled again at 8,000 hours at which time all items would be correctly phased into their proper block/pattern. Consideration should be given by the assigned inspectors to the extent of inspection (overhaul) required in the case of initial overhauls that are accomplished early solely for the purpose of phasing an aircraft into a block/pattern system.
In the foregoing example, it can readily be seen that block A items at the time of initial overhaul by the buyer will actually have accumulated only 5,000 hours since previously overhauled while block/pattern C items will have accumulated 9,000 hours.
In either case it must be remembered that another 8,000 hours will pass before they are overhauled again.
---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 5. FORMAT FOR PRESENTATION OF PRORATION
DATA ON AIRCRAFT BEING TRANSFERRED Previous Operator (__________) Buyer (_________) Identify Identify
Block/Pattern Approved Time Percent of Approved Pro- Proor Component Overhaul Since Overhaul Overhaul rated rated & Serial No. Time Over- Time Used Time T.S.O. Time haul To Overhaul (16000) Respective (12000) Respective Block/ Block/ Pattern Pattern Block/Pattern A 4000 3000 .187 12000 2244 9756 Block/Pattern B 4000 15000 .937 12000 11244 756 Block/Pattern C 4000 11000 .687 12000 8244 3756 Block/Pattern D 4000 7000 .437 12000 5244 6756 ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 6. TRANSFER OF PREVIOUSLY PRORATED AIRCRAFT An aircraft was acquired by operator "X" and placed on his maintenance program through the proration process. After acquisition, "X" operated the aircraft for an additional 1,000 hours.
1. 12,000 hours = approved overhaul time for "X".
2. 3,000 hours = prorated TSO for "X" at time of acquisition.
3. 2,000 hours = actual TSO at time of acquisition by "X".
4. 1,000 hours = additional flight time added to aircraft by "X".
5. 3,000 + 1,000 = 4,000 hours - "X's" prorated TSO.
6. 2,000 + 1,000 = 3,000 hours - actual TSO on aircraft.
Operator "X" now desires to transfer the aircraft to operator "Y". The overhaul time is to be prorated for operator "Y" and his approved overhaul time is 14,000 hours.
7. 3,000 divided by 12,000 = .250 of overhaul time used by "X".
8. 14,000 hours = approved O.H. time for "Y".
9. 14,000 x .250 = 3,500 hours prorated TSO for "Y".
10. 14,000 - 3,500 = 10,500 hours remaining to overhaul for operator "Y" at time of transfer.
NOTE: Actual TSO (Step 7) was used for purpose of proration to operator "Y", not the prorated TSO.
* The buyer of a previously prorated aircraft whose approved overhaul time limits are identical to the previous operators may utilize the remaining prorated time of the previous operator.
When a buyer uses the remaining prorated time, a document shall be prepared listing the previous operator or operators' approved overhaul times on which the proration was based and shall be made part of the operations specifications by means of a preface page such as the example shown in Appendix 1, Figure 12. * ---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 7. PROCEDURES FOR CONVERTING CALENDAR OVERHAUL (MONTHS) TO HOURS SINCE OVERHAUL FOR PRORATION
PURPOSES
METHOD A Previous operator's overhaul time limit is 18 months: (360 + 180 = 540.
Previous operator's time since overhaul is 180 days.
Buyer's approved overhaul time limit is 2,000 hours.
COMPUTATIONS 180 --- = .333 time since overhaul.
540 .33 of 2,000 hours = 666 hours prorated time since overhaul for buyer.
2,000 hours - 666 = 1,334 hours. Buyer's prorated time remaining to overhaul.
METHOD B Previous operator's overhaul time limit: 18 months or 540 days.
Previous operator's utilization time: 8 hours per day.
Previous operator's overhaul time limit in hours: (540 days x 8 hrs.) = 4,320.
Previous operator's time since overhaul (180 x 8 hours) = 1,440 hours.
Buyer's overhaul time limit is 2,000 hours.
COMPUTATIONS 1400 Time since overhaul in percent: ---- = .333 4320 .333 of 2,000 hours = 666 hours prorated time since overhaul.
2,000 hours - 666 = 1,334 hours. Buyer's prorated time remaining to overhaul.
---------------------------------------------------------------- ---------------------------------------------------------------- FIGURE 8. METHOD OF DEPICTING AREAS, SECTIONS, COMPONENTS, ETC.,
THAT ARE TIED TO A SPECIFIC BLOCK The following presentation is an example of how items such as areas, sections, and appliances are included in a block.
An operator should submit such items and relate the items to the block, or submit actual time for each item.
Block/Pattern Block/Pattern Block/Pattern Block/Pattern
A B C D Nose gear Center Section Right wing fuel Empennage assembly & cells components Steering Left wing fuel Lights Ruddermechanism & cells vertical fin controls Accumulators Pylons, Nos. Electrical Stabilizer 1 & 2 units, components, connections, Nose gear doors Lines etc.
Brackets, Electrical Hydraulics Tail hinges, etc. connections Compartment Lights, wires, Flaps Lights etc.
Air inlets & Spoilers Booster anti-icing control Hydraulic