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New Lycoming Prop Strike AD

sj

Staff member
Northwest Arkansas
Anybody with a Lycoming Engine just received an AD notice from the FAA concering grounding the aircraft until an inspection has been made of the crankshaft bolts and gears on aircraft that have had a prop strike. They also (in my opinion) made the definition of "prop strike" very loose, and to include any loss of rpm caused by grass, water, etc. Heck!

What are your thoughts on this? How tough is the inspection?

Here is the summary:

SUMMARY: The FAA is adopting a new airworthiness directive (AD) that supersedes an existing AD, for Lycoming Engines (formerly Textron Lycoming), direct-drive reciprocating engines (except O-145, O-320H, O- 360E, LO-360E, LTO-360E, O-435, and TIO-541 series engines). That AD currently requires inspection of the crankshaft gear installation and rework or replacement of the gears where necessary after a propeller strike, sudden stoppage, at overhaul, or whenever gear train repair is required. This AD requires the same actions but makes the correction that the existing gear retaining bolt and lockplate be removed from service and new hardware installed, and revises the definitions for sudden stoppage and propeller strike. This AD results from a change to the definition of a propeller strike or sudden stoppage. We are issuing this AD to prevent loosening or failure of the crankshaft gear retaining bolt, which may cause sudden engine failure.

DATES: This AD becomes effective June 25, 2004. The Director of the Federal Register approved the incorporation by reference of certain publications listed in the regulations as of June 25, 2004.

Definition of Propeller Strike
(i) For the purposes of this AD, a propeller strike is defined as follows:

(1) Any incident, whether or not the engine is operating, that requires repair to the propeller other than minor dressing of the blades.

(2) Any incident during engine operation in which the propeller impacts a solid object that causes a drop in revolutions per minute (RPM) and also requires structural repair of the propeller (incidents requiring only paint touch-up are not included). This is not restricted to propeller strikes against the ground.

(3) A sudden RPM drop while impacting water, tall grass, or similar yielding medium, where propeller damage is not normally incurred.

(j) The preceding definitions include situations where an aircraft is stationary and the landing gear collapses causing one or more blades to be substantially bent, or where a hanger door (or other object) strikes the propeller blade. These cases should be handled as sudden stoppages because of potentially severe side loading on the crankshaft flange, front bearing, and seal.
sj
 
Steve,

Lycoming has had this out in a service bulletin for some time. While that was not mandatory for compliance by part 91 operators, it would be pretty hard to get by without compliance, simply due to liability, and getting a maintenance shop to sign anything off after a prop strike.

I agree that the definitions seem pretty draconian, but you also have to understand that they've seen some cranks that were destroyed by what had appeared to be minor prop strikes as described.

Anyway, the cost of dinging your prop has certainly gone up in recent years, and it is'nt going to get better.

Be careful with those props.

MTV
 
I think the AD is less restrictive than my personal standards. A sudded RPM drop caused by something grabbing your prop should be cause for concern. Have you ever had a noticable RPM drop from contact with grass or water? I haven't, but if I was churning enough of either, this AD would be the least of my concerns.

Steve, If you've never flown floats before, you're about to see just how destructive common prop spray can be to a prop. This AD isn't talking about common contact.
SB
 
Stewart, I have seen the hydraulic damage of which you speak, especially on amphip equipped planes. The straight floats don't seem to do it near as bad.

sj
 
Steve,
And never is it as apparent as right after you install a new prop!
SB
 
Technically, I installed a used prop, so it won't be QUITE as bad...

sj
 
I would respectfully add that a LOT of this has specifically to do with operator technique. Pay close attention to your prop, the wind, and your taxi speed, and use of power only when absolutely necessary, and then accompanied by full aft stick, and you won't have problems.

I see LOTS of examples, on both wheels and floats, of really bad technique resulting in totally unecessary damage to propellers.

As Stewart notes, this AD specifically addresses the prop coming into contact with something. That said, running your prop through a little wet grass may not be a big deal. If the engine slows as a consequence, though, this thing will apply.

I know of a guy this last winter (135 operator) who landed on wheel skis on other than snow, for whatever reason, plane went forward to the check cables, and the prop (on an O-360 Cub) just barely contacted the pavement. He didn't even remove a 1/16th of an inch of material, and the prop never stopped, and it was at idle. Mandatory teardown, which found no problems.

MTV
 
That sounds to me like minor dressing of the prop which doesn't fall into a sudden stopage. I think the definition is a good one, basically if you can repair the prop properly without removing it and there was no noticable drop in RPM there is no strike
 
Cimarron,

If the prop hits ANYTHING, its considered a strike according to this AD, as noted, even wet grass, let alone ground.

Minor dressing won't make it. Especially with the FAA watching, as was the case here.

MTV
 
Mike,
Did we read the same AD? Contact that causes an RPM loss or prop damage beyond what can be dressed-out defines a strike, at least that's what I read.
SB[/b]
 
SB

Thats the way I read it too. If the prop needs to be removed to repair it tear down the engine. Continental or lycoming no diference.

I don't care if the FAA is watching, I have been known to give them lessons in reading too. :morning:
 
What are you guys hearing from the engine shops/mechanics that tear these "prop challenged" engines down? 2 overhaul facilities that I have spoken with have not detected any interior damage on O-320's and 360's from prop strikes(not counting bent flanges)........and they said some were high RPM strikes. I would think it would all depend on what the prop strikes........tall grass or brush should yield a gradual( even if it is sudden) RPM where I suppose if you hit a concrete block or steel pipe it's a different story. Personally I think the AD is an overkill with the "tall grass" requirement.
 
Water is pretty hard on the prop. If a sudden drop in RPM occurs, you are no longer a plane but rather a submarine.

Plow turns and constantly going on and off from the step will eat the prop. If time is not a concern, taxi at idle. And as mentioned earlier, stick back when applying power and hold the stick back when you touchdown.
 
That advice is appropriate if you fly on and off of lakes on calm days. Try a river that's got strong current, standing waves, and sandbars. Or idiot boaters that think you've got brakes as they head right at you in a curve. Or jet-skiers driving forward while looking behind them. Or taxi in a 30mph wind that's white-capping the water. There are moments when every float pilot must say "Screw the prop, fly the plane."
SB
 
Note that the AD says "a loss of rpm OR prop damage that cannot be dressed out".

That means, Cimarron, that if there is ANY loss of rpm, whether or not there is ANY damage apparent to the propeller blades, that a teardown is required.

There's a difference between the word "or" and the word "and", and the FAA knows that. You can give them reading lessons all you want, but it probably won't work in this case, cause you're the one not reading the AD.

If you're a 135 operator, you don't have much choice about compliance, particularly if the FAA is watching.

I think this thing is overkill + CYA, but there's not much you can do about it.

I do think that the prop damage that Stewart is referring to on floats is not what this addresses, though he's right that at times you got to get with the program.

MTV
 
I understand what you are saying but..... It wiuld be very hard to prove that there was a loss of rpm due to a strike when the fed isn't in the cockpit with his hand on the throttle. Also, though I haven't seen everything I have never seen a noticable drop in rpm on an engine due to a prop strike where there wasn't prop damage, either bending as in a water or snow strike or tip damage from something hard. I also agree with the AD that if something external slows the engine rapidly it can cause problems in the gears.
 
Actually, the fed was standing alongside the runway. Hearing works too. It's a small world sometimes.

Besides, the onus is always on the owner to fess up, and this AD applies as well. Lycoming is concerned that a loss of rpm may cause damage internally. Do with it what you will, it's on your conciense.

I've seen several propellers, particularly Borer props, which are very thin, severely bent due to running them through snow. I can't tell you if there was an rpm drop, cause I wasn't driving it when it got twisted, but I can tell you they don't pull for beans after being treated that way.

Your statement also doesn't make sense, in that you assert that you've never seen an rpm drop that didn't cause prop damage. Prop damage may be incurred, but possibly dressed out with normal techniques, as was the case with the guy here.

You can have a significant rpm drop under a number of circumstances while doing only "minor" damage to the prop, ie: damage that can be dressed out using standard procedures.

Again, this is Lycoming saying that they've seen some problems. I don't have any evidence to the contrary, and I don't tear down engines, or investigate accidents, so I'd have trouble arguing the point.

MTV
 
It is lycoming covering their a$$. I have torn down several engines that were prop strikes. Many were idling and the prop was repaired by a prop shop. Have yet to find anything else wrong but I covered my butt. Knew of a Citabria that bent the prop so bad it had to be replaced. They had a hard time explaining to the FAA why they replaced a prop that had 100 hrs. on it and a few hours later the crank broke. Comon senseout the window.
 
Steve,

I agree. The problem is those "tweeners". That is, the prop "strikes" that fall in between the extremes.

What you do there is subject to a lot of debate.

MTV
 
And the cheap skates who don't do what obviously needs to be done bring regulation down on the rest of us.
 
I bought my Champ as a 'basket case', after a groundloop & prop strike. It's a C-90, rather than a Lycoming, but they suffer some of the same effectes, I s'pose.

One blade of the prop was curled back about 18 inches from the end. The bend was 2 degrees short of the maximum allowed, so we could have repaired it, had it not been under the minimum dimensions as far as overall serviceability.

Anyway, when the engine was torn down, no strike damage was found - as expected, since the prop flange ran true with a dial indicator. However, we *did* find all kinds of other ugly stuff, and $9000 later, I have my engine back on the airframe. No prop, yet; that'll be another couple thousand. This was a 400 SMOH engine, although most of the overhaul was done with a pencil, it turned out. What can you expect from a A&P/IA that hangs an illegal prop on it?

Jon
 
Ya know, I had nearly precisely the same experience some years ago.

Ain't these folks grand?

MTV
 
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