The Beechcraft 1900D is a popular turboprop aircraft. With more than 380 aircraft in service, many mechanics are working on these venerable aircraft. On Sept. 20, 2004, Pratt & Whitney Canada (P&WC) issued Service Bulletin 14003R10. This service bulletin affects the PT6A-67D and -67R engines. I talked to Kris Charlesworth of Raytheon Airline Aviation Services, who worked with P&WC in developing this latest revision to the service bulletin, to gain a little more insight into how it works. In this article, we will look at some of the key points of the revision, and how it affects operators of 1900s.
Extending TBO
The crux of SB 14003R10 deals with recommended basic operating time between overhaul (TBO) and hot section inspection (HSI) frequency. The pre-established frequencies of periodic inspections issued by P&WC help ensure engine serviceability. The TBO and HSI intervals are the two major scheduled periodic inspections for these engines and are discussed in SB 14003R10. In addition, the SB provides TBO extension and progressive maintenance procedures for operators with an average utilization higher than 500 hours per year.
TBO categories
SB 14003R10 has three major categories of TBO -- basic, fleet, and engine.
Basic TBO. The basic industry TBO is P&WC's recommended TBO per the service bulletin and is applicable to all operators.
Fleet TBO extension. This is a TBO extension granted by P&WC for an operator with a fleet of similarly operated and maintained engines. P&WC uses the condition of the engines when they are examined at overhaul as the primary means of validating that the operator is operating and maintaining the engines in a manner that warrants extending the TBO interval for a specific fleet.
Engine TBO extension. This TBO extension is applicable to a specific engine. TBO extension under this case is granted for a specific engine and is granted on an engine-by-engine basis (vs. the fleet TBO above).
Under this SB, all TBO extensions go through P&WC for approval. Extension recommendations from P&WC are based on both the operator's procedures and experience, and on the experience of P&WC. P&WC's experience takes the following factors into consideration.
- Engines are built only with new P&WC recommended components, components refurbished by P&WC owned shops, or components refurbished by P&WC recommended shops per P&WC procedures.
- The engines are P&WC factory built engines or engines overhauled/repaired at a P&WC service center or a P&WC Distributor and Designated Overhaul Facility (DDOF).
An important thing to note is that once TBO extension is recommended by P&WC under the SB, the engine maintains its TBO extension recommendation as long as it is operated within the limitations established in the operating manuals and maintained in accordance with the maintenance manual and the terms of SB 14003R10.
Prior to this new SB revision, operators had to go through a lot to get a TBO extension on their engine. They had to go through the local Pratt representative, and it was considered a cumbersome process.
Variables affecting TBO extension
There are several variables that are considered when reviewing whether or not the TBO should be extended. These include:
- Average flight duration
- Percentage of time at any given power level
- Climatic conditions and environment
- Maintenance practices
- Utilization
- Engine modification standards
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.
Option B
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.
Application process
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.
Midlife inspection
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:
- Compliance with all applicable inspection SBs is verified.
- A full hot section inspection is performed. Exposed gas generator surfaces must be corrosion-free and all missing diffusor ducts must be replaced. Turbine blades must show no or minimal sulphidation (stage 1 maximum allowable).
- Ensure compressor is free of corrosion.
- All foreign object damage to compressor must be repaired.
- Inspect the AGB starter generator drive pad splines for wear.
- Ensure all external surfaces meet all corrosion and damage requirements. Repair generator and cast housing surfaces with touch-up paint. Clean and inspect the gas generator drain valves.
- Remove and inspect the external pneumatic hoses and tubes (Px and Py tubes) for cracks or other damage.
- Perform all oil system checks.
- Inspect accessories. Inspect controls, linkages, leads and connectors. Check temperature indicating system including T1 probe trim resistance.
- Check the operation and/or calibration of all engine-related instrumentation.
Option B also includes operation and maintenance requirements that need to be maintained once an engine is registered on the program including engine performance monitoring, compressor washes, fuel nozzle inspections, compressor first-stage inspections, engine control checks and adjustments, propeller balancing, and instrument gauge checks. A yearly report must be supplied to P&WC with a status update relative to these operation and maintenance requirements.
This has been a brief primer on some of the changes in SB 14003 that affect 1900 operators. For more information, contact P&WC or Raytheon Airline Aviation Services.
Additional ReSources
Pratt & Whitney Canada
www.pwc.ca
Raytheon Airline Aviation Services
www.airliner.raytheonaircraft.com
