In fact, in some cases such as extremely low utilization rates coupled with continuous operation in a salt water atmosphere or a heavy sand or dust environment, periodic inspections performed on the engine may indicate that maintenance action is necessary prior to the recommended overhaul life.
The crux of the changes implemented in SB14003R10 affect Engine TBO extensions on an engine basis and we will look into that portion a little more.
The portion of SB 14003R10 that pertains to engine specific extensions is Option B. Whereas Option A is relevant to Fleet TBO extensions, this option is uses for TBO extension on a single engine. For TBO extension recommendations under this option, the following time limits are in effect:
Overhaul: TBO is 9,000 hours or 14 years, whichever comes first (since new or since overhaul as applicable).
HSI: Perform at least once in a 6,000-hour period. This may be performed as part of the midlife inspection.
Some of the eligibility factors for TBO extension recommendation include:
- The engine must incorporate all service bulletins listed in the Appendix of the SB Paragraph 4.C at the first opportunity and no later than the midlife inspection.
- Components listed in the Appendix, Para. 4.B (4) are subject to a recommended time limit in service of 16,000 hours TSN, except 12,000 hours TSN for the second stage power turbine blades. For any listed components that will reach their time in service prior to the next planned shop visit, replacement must be scheduled prior to or when reaching their time limit.
- The aircraft must be equipped with an approved exceedance engine monitor.
- Engines must have a minimum utilization of 30 hours/month. For occasional lower utilization or aircraft maintenance or storage, engines should be run weekly or be preserved in accordance with the engine maintenance manual.
To apply for a TBO extension under Option B, the operator completes the TBO application/checklist provided in the service bulletin. This application includes data such as engine model and serial number, total time, and time since overhaul. It also covers the operator's mission profile including whether or not the engine is operated at sustained high power or in extreme conditions. Average hours per month and the average cycle-to-hour ratio is included. P&WC states in the SB that missions which involve an unusually high ratio of cycles to flight hours or unusually protracted use of high power may not be eligible. The checklist also documents engine assembly and component records and service bulletin and accessory configuration records.
In addition to the above information on the engine itself, operator information is required. This includes information such as PT6A maintenance experience, the type of quality assurance program in place, maintenance tracking, facility, publications, maintenance personnel, personnel training, and tooling.
A main component of TBO extension under Option B is the engine midlife inspection. This inspection should be scheduled between 4,000 hours and the operator's TBO. The midlife inspection requirements do not need to be carried out concurrently. When scheduling midlife inspections, the operator must also consider other limitations such as component time limits and cyclic limits per SB 14002. The midlife inspection procedures must be accomplished by a P&WC DDOF facility, representative, or M.O. recommended for the procedures carried out. Items in the midlife inspection include:
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