One was a complete melt down of the compressor turbine which took out the power turbine. The 2nd one was a melt-down of the compressor turbine. The power turbine was damaged at the same time. Very long story associated with the 2nd one.
I've also heard of a time a shaft bearing began to fail allowing the shaft to wonder and vibrate so badly it broke the #3 bearing surface free from the rest of the case.

As far as i know, all of the failures were not associated with FOD. We do allot of temp changes compared to "start, takeoff, cruise, land, shutdown" type of flying. Some of our engines have 5+ times more start/shutdown cycles than they do hours.

 

Most common problem I've heard of for engine failures is the fuel pump.

 

In-house overhauls?

 

Unless the FAA grants an extension beyond the TBO, the MORE program is the only way to legally fly past the 3600 (or 3000 or 3500 depending on model) hours. It's not like a piston where under 91 you can over fly it. The when PWC certified the PT6, part of the Type Certificate was a mandate to comply with all manufacturer service bulletins. One SB specifies the TBO as well as another that specifies certain components are life-limited by hours or cycles. Those SB's, regardless of whether you are 91 or 135, must be complied with. If the engine has been run for 400 hrs beyond TBO, then there is documentation to support it. If the operator was allowed to run it like that without the MORE STC, then I am pretty sure there is another specified limit, and the ability to operate it like that remains with the operator because that operator's maintenance program and operational history was the basis for the extension. In other words, in this situation I believe when the operator sells the plane, the engines are due.

 

The ability to run over TBO is specific to the 90 series and how Beech wrote the manuals. There is no chapter 4 in the manual which would list the life limited parts, and per 91.403(e) there are no administrator approved documents that say you can't run over TBO. The only parts listed are the internal cycle limited parts, most of which are around 18,000 cycles.

 

It wouldn't be in the Beech manual since PWC made and certified the airframe. The FAA approved document is the TCDS for the PT6 which, in Note 14, referenced the TBO and Service Life SBs (SB1803 iirc for the -21/28 TBO). This wraps those SBs into the airworthiness requirement for that engine. FWIW that SB also addresses the extension policies relating to transfer. The MORE site has additional info on this in the FAQ section. As for components, the Gen is 2500 and the FCU I think is 4100 hrs. Some older disks have 8000 cycle lifves, too. You just have to check what parts are installed in the specific engine.

 

Yes they are...

 

http://rgl.faa.gov/Regulatory_and_Gu...light=ne-12-04

rgl.faa.gov/Regulatory_and_Guidance_Library/rgSAIB.nsf/0/e25f6328688614ab8625793b006a2d76/$FILE/NE-12-04.pdf

SUBJ: Turbine/ Turboprop Engine: Reduction Gearbox
Date:
November 1, 2011
This is information only. Recommendations aren’t mandatory.
Introduction
This Special Airworthiness Information Bulletin (SAIB) alerts owners, operators, and certificated repair facilities of airplanes equipped with Pratt & Whitney Canada Corp. (PWC) PT6A-6, PT6A-6A, PT6A-6B, PT6A-11, PT6A-11AG, PT6A-6/C20, PT6A-20, PT6A-20A, PT6A-20B, PT6A-21, PT6A-15AG, PT6A-25, PT6A-25A, PT6A-25C, PT6A-27, PT6A-28, PT6A-34, PT6A-34AG, PT6A-34B, PT6A-35, PT6A-36, PT6A-110, PT6A-112, PT6A-114, PT6A-114A, PT6A-121, PT6A-135, and PT6A-135A series turboprop engines of the potential for engine in-flight shutdowns (IFSDs) as a result of premature failure of the reduction gearbox.
These engines are installed on, but not limited to, Air Tractor AT 402A/402B, Air Tractor AT 502B, Ayers Turbo Thrush T-15, Ayers Turbo Thrush T-34, CATIC/HAIG Y-12, Cessna Conquest I, Cessna 208/208B Caravan I, DeHavilland DHC-6 Twin Otter Series 300, Embraer EMB-312 Tucano, Embraer Bandeirante EMB-110, Embraer Bandeirante EMB-111, Embraer Caraja, Embraer EMB-121 XINGU II, Frakes Turbo Cat Model A/B/C, Frakes Mallard, JetPROP DLX, LET L410, Pacific Aero Cresco 750, Pacific Aero Cresco 750XL, PIAGGIO P-166-DL3, Pilatus Turbo Trainer PC-7/PC-7 MKII, Pilatus Turbo Porter PC-6, Piper Cheyenne IA, Piper T1040, Piper Cheyenne II/IIXL, PZL-Okecie PZL-130 TC-II Turbo-Orlik, PZL-Okecie PZL-106 Turbo-Kruk, PZL-Okecie PZL-130 TE Turbo-Orlik, Raytheon Beech 99, Raytheon Beech 99A, Raytheon Beech King Air C90A/B/SE, Raytheon Beech C99 Airliner, Raytheon Beech T-34C, Raytheon Beech King Air A100, Raytheon Beech King Air E90, Raytheon Beech T-44A, Raytheon Beech King Air F90-1, Raytheon Beech King Air C90GT, Reims F406 Caravan II, Schweizer G-164B AG-Cat Turbine, Schweizer G-164D AG-Cat Turbine, Turbine Air Bonanza, and Vazar Dash 3 Turbine Otter series airplanes.
The airworthiness concern is not an unsafe condition that would warrant airworthiness directive (AD) action under Title 14 of the Code of Federal Regulations (14 CFR) part 39.
Background
Three first stage reduction sun gear and planet gear failures have occurred within a recent 18 month period. The engine IFSDs addressed by this SAIB are due to some operators and overhaul shops not following the PWC overhaul manual (OHM) criteria for reduction gearbox first stage reduction sun gear and planet gear replacement. Not complying with OHM procedures is a significant contributor to first stage reduction sun gear failures.
Recommendations
To prevent reduction gearbox failure, we recommend:
1.
Following the maintenance practices in the applicable OHM.
2.
Replacing the first stage reduction sun gear and planet gears with a complete zero time, first stage reduction sun gear and planet gear matched set at every replacement.
3.
Replacing the first stage reduction sun gear and planet gears at next overhaul, if one of the following apply:
1
2
a.)
Planet and sun gears were not installed as a complete zero time matched set at prior repair or overhaul, or
b.)
Planet gears were reversed and re-installed at a prior repair or overhaul.
4.
Replacing the first stage reduction sun gear and planet gears, not covered by Recommendation 3. of this SAIB, within 12,000 hours total time-since-new. Information on replacement can be found in the applicable Engine Operating Time Between Overhauls and Hot Section Inspection Frequency service bulletin.
For Further Information Contact
James Lawrence, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803; e-mail: [email protected]; phone: (781) 238-7176; fax: (781) 238-7199.