Caravan AD... Ouch!

ppragman

FLIPY FLAPS!
http://www.avweb.com/avwebflash/news/Potentially-Expensive-New-AD-for-PT6-Engines222719-1.html

Potentially Expensive New AD for PT6 Engines


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By Rick Durden | September 3, 2014

Five Killed In Colorado Crash




A new Airworthiness Directive (AD) will require initial and repetitive borescope inspections of some 300 PT6A engines and potentially cost operators as much as $18,106,200. Following reports of compressor turbine (CT) blade failures causing engine power loss, the FAA issued an AD Wednesday that requires replacement of blades that fail inspection with a newly developed blade. The purpose of the AD is to prevent failure of CT blades, which the FAA said “could result in damage to the engine and damage to the airplane.” It becomes effective October 8. Affected engines are Pratt & Whitney Canada (P & W) PT6A-114 and PT6A-114A engines.

According to the FAA, “There have been a number of reported incidents where Compressor Turbine (CT) blade failures have caused power loss on PT6A-114 & PT6A-114A engines, resulting in in-flight shutdown.” The FAA went on to say that Pratt & Whitney’s investigation revealed that high power and high temperature operations could cause the CT blades to crack or break because of “creep” or sulfidation. P & W developed a new CT blade that is less affected by creep and published specific inspection requirements for engines with affected CT blades. The engines are most commonly installed on Cessna 208 Caravans, where an inflight shutdown means a forced landing. The FAA estimates the inspection will require four hours—with eight hours to replace blades, if required. Should all of the old-style blades require replacement, the cost is estimated to be about $59,334 per engine.
 

Goreman11

Well-Known Member
Link this to the topic of operators running them all out all the time. Guess it pays to pull the power and prop back a little.
 

CFI A&P

Exploring the world one toilet at a time.
Hmm... The AD says it will affect 300 airplanes of US registry. It seems like that is a little light. Seems like there are more than 300 Caravans out there flying bull semen, boxes, meat missiles, seaplanes, aerial survey operators...
 

JeppUpdater

Well-Known Member
We (like most scheduled operators, I'm sure) run power settings quite reduced from what Cessna/Pratt permit to extend the TBO and do daily trends to monitor the engines. Quite a fascinating process really and gives excellent info when the pilots are properly trained to do reliable and consistent trends. We also borescope every 200 hours as part of a normal phase inspection. I don't see too many scheduled operators being hit too hard by this, honestly. But that's just my opinion - I'll find out more and post what I can once I get back from this ridiculous cross country jaunt.

I did enjoy this gem from that document:
An engine power loss or IFSD on a single engine powered aeroplane such as Cessna 208 could result in an unsafe condition.
 

Capt. Chaos

Well-Known Member
Funny that the Canadians are allowing relief with the blades that we're not required to be inspected under the previous SB, while the FAA is only allowing the new single crystal blades.
 

DPApilot

GUYSH! GUYSH! GUYSH!
JeppUpdater said:
We (like most scheduled operators, I'm sure) run power settings quite reduced from what Cessna/Pratt permit to extend the TBO and do daily trends to monitor the engines. Quite a fascinating process really and gives excellent info when the pilots are properly trained to do reliable and consistent trends. We also borescope every 200 hours as part of a normal phase inspection. I don't see too many scheduled operators being hit too hard by this, honestly. But that's just my opinion - I'll find out more and post what I can once I get back from this ridiculous cross country jaunt. I did enjoy this gem from that document:
Shocking, isn't it? Don't run the engines at max power and they last longer....
 

Goreman11

Well-Known Member
Every single engine is under powered if you ask me.

On the serious side I don't think it's that bad. I have been in twins that do worse at max gross then the 208 does.
 

gotWXdagain

Highly Visible Member
What good would pulling the prop back do? It's not connected to it.
Just because it's a free turbine engine doesn't mean the prop works completely independently of what's happening inside the turbine section. If the prop is commanded to spin faster, the free turbine must also spin faster - it is mechanically linked to the prop, after all, via reduction gear. Changing the free turbine RPM is going to change the airflow through the turbine section, which would have an effect on the temperatures inside the turbine. Whether an RPM increase actually results in a temp increase, I'm not really sure, but you can't change one without seeing the other change.
 

Roger Roger

Paid to sleep, fly for fun
Just because it's a free turbine engine doesn't mean the prop works completely independently of what's happening inside the turbine section. If the prop is commanded to spin faster, the free turbine must also spin faster - it is mechanically linked to the prop, after all, via reduction gear. Changing the free turbine RPM is going to change the airflow through the turbine section, which would have an effect on the temperatures inside the turbine. Whether an RPM increase actually results in a temp increase, I'm not really sure, but you can't change one without seeing the other change.
Typically a higher RPM actually results in a lower ITT/EGT/TIT due to increased mass airflow through the engine.

*edit* aaaand turbine inlet temperature is censored. THANKS OBAMA!
 

Roger Roger

Paid to sleep, fly for fun
Every single engine is under powered if you ask me.

On the serious side I don't think it's that bad. I have been in twins that do worse at max gross then the 208 does.
The van with 900 HP is appropriately powered. I can't even imagine flying with with a permanent block at 75% power temp limited even lower at altitude.
 

gotWXdagain

Highly Visible Member
Typically a higher RPM actually results in a lower ITT/EGT/ due to increased mass airflow through the engine.

*edit* aaaand turbine inlet temperature is censored. THANKS OBAMA!
That's what I was thinking too. The mass airflow has to do more work to move the power turbine when it's loaded at lower RPM's than when it's loaded at higher RPM's.

Unfortunately my variety of PT6A and airplane combo doesn't give me control over Np.
 

Beep

Well-Known Member
Call me crazy, but this doesn't sound all that expensive. Approximately four hours of labor if there aren't any problems found?
$59,334 if you have to replace the blades, that is unfortunate, but still not something that should be considered excessive... If the owner can afford the airplane that is.
Maybe it's just because I'm not familiar with the annual operating costs, but I don't see the problem.
 
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