Grumman Tiger Looses Its Propeller

[BigTex]

http://www.therepublic.com/view/story/acf7ae6d70fd4c9797b909c7531c42fd/TX--Plane-Lost-Propeller

 

So folks.... I saw him interviewed after his off field landing and he was kind of laughing this off.  I don't know about you but the last thing I'd be doing is cracking jokes.  Me and my soon to be ex A&P would have a frank and honest conversation.  Definitely will have some explaining to do.

[M016576]

Depends on how long that prop had been in service and when it was last torn down. If the prop was 15 years since new, with 2000 hours on it, then this wouldn't surprise me too much. Not really the A&P's fault in that case. But it could be. Hard to say without all the facts. What I do know is that It doesn't take long for a crack to split at those speeds / forces. If I walked away unscathed after the whole prop left the plane, I'd be pretty happy.

[jetdriven]

Prop failures are rare, but on the tiger without a split nose bowl you must remove the prop to remove the entire lower cowl. This may be at work here.

"During telephone interviews conducted by the NTSB IIC, both STC owners stated that during installation of the propeller, the aft spinner bulkhead can slip off of the bushings and rest against the propeller bolts. When the bolts are torqued, the aft spinner bulkhead is pinched between the propeller spacer and the bushings. Eventually, half-moon or crescent shaped arcs of aluminum are punched out of the aft spinner bulkhead material, elongating the bolt holes and leaving the propeller loose."

http://www.ntsb.gov/aviationquery/brief2.aspx?ev_id=20001212X18760&ntsbno=FTW99FA132&akey=1

[Alan Fox]

So I guess its the mechanics fault if the prop or crank fails....great attitude.....

[jetdriven]

No I said it may be the cause. Notice in those photos that the spinner and spinner backplate is missing as well. That's not indicative of a prop splitting in two. Further the prop comes off every annual. And a previous accident resulted from difficulty getting the prop seated fully before torquing it. The crank may have snapped off, hopefully they find out. I also work in a shop and think about the consequences of leaving something undone or not assembled properly.

If thinking about it logically makes me an ass, then I'm guilty as charged.

[Guest]

http://www.therepublic.com/view/story/acf7ae6d70fd4c9797b909c7531c42fd/TX--Plane-Lost-Propeller

 

So folks.... I saw him interviewed after his off field landing and he was kind of laughing this off.  I don't know about you but the last thing I'd be doing is cracking jokes.  Me and my soon to be ex A&P would have a frank and honest conversation.  Definitely will have some explaining to do.

Without more facts its a bit premature to blame the maintainer. There is in fact a recurring AD on the original McCauley prop calling for a NDT inspection each two hundred hours. Prehaps it was a cheap ass owner who placed his wallet ahead of safety.

Clarence

[PTK]

I look at it this way. I'd much rather prefer the entire prop depart the airplane than a fractured off piece of blade!

[kerry]

 

Here's a 172 that lost a prop.  They seemed very happy after landing

[Alan Fox]

It could be a failed crankshaft as well..

[tony]

 The pilot is responsible for the airworthiness of his or her airplane.  Not the mechanic.

[BigTex]

The pilot is responsible for the airworthiness of his or her airplane. Not the mechanic.

So maintenance induced failures is now the pilot's fault?

[RJBrown]

The mechanic is responsible and liable for any acts or omissions not complying with the proper assembly of a component. Shifting the responcibilities of the CERTIFIED mechanic to the pilot is not the intention of that phrase. A pilot can legally and reasonably assume that the work was done properly when signed off by certified maintainence personel.

 The statement "The pilot is responsible for the airworthiness of his or her airplane. Not the mechanic." is grossly ignorant and outside of the intended context when applied in this fashion.

[Alan Fox]

Actually like it or not the ultimate responsibility is with the pilot in command , I do think that this is going to be a Crank failure , There is an AD on lycoming crankshafts for fixed pitch props , that has to do with corrosion pitting on the inner  bore of the crank , It is not pertinent on constant speed props as they are filled with engine oil .... 

[Guest]

If the Tiger had the correct engine installed, sb 505 and the associated AD don't apply, it's a solid crank engine and therefore exempt.

Clarence

[PTK]

The owner/operator is primarily responsible for airworthiness and properly managing the maintence of the aircraft. This includes making sure all maintenance and inspections are completed in a timely fashion and all actions are properly logged.

Once maintenance has been directed and approved by owner/operator and mechanic has been allowed to proceed the latter is responsible and liable for performing it properly.

Proper documentation is the key and ultimately this is the owner/operator's responsibility.

[Rustler]

For Those Interested--

 

Here is a letter posted by the developer of the STC for that prop.

 

 

TIGER OWNERS, LISTEN UP!


This subject is very real and needs to be addressed. The current incident
being discussed is serious and there have been several incidents involving
the propeller departing the aircraft during flight. Most have been the
original McCauley splitting apart from a crack developing through the hub at
the propeller bolt holes but, as in the case involving Sen. Inhofe, it was a
Sensenich that the bolts just loosened and it "outran" the airplane. I was
drawn into this investigation by the NTSB and the FAA as being the developer
of the STCs for installing the Sensenich props in the first place. As
understand, the propeller was found in a field, about 3 miles back of where
he landed the airplane, with the spinner still attached and the prop bolts
still safety wired together in the prop. The bolts were broken off at the
back of the spacer. (Now, I didn't see it, or even a photo, but this was
the description I got from the NTSB investigator.)



What I suspect happened is the backplate was not secured when the bolts were
torqued down resulting in a "false torque" that eventually allowed the prop
to begin moving a little causing the holes to begin enlarging around the
propeller drive bushings with the eventual result of all 6 bolts failing and
the prop leaving the plane behind. To understand this a little better, the
"propeller drive bushing" are the things pressed into the crankshaft flange
that the propeller spacer seats onto. In the Tiger's case, these bushings
are really too short for the installation of a fixed pitch propeller. There
are a total of 6 bushings of which 2 barely come through the crank flange
and starter ring gear support assy. at all and the other 2 are only a
quarter inch or less protruding. The original spinner system used a flat
backplate that was sandwiched in between the propeller and spacer. This
left no possibility for the problem that came with the development of the
"Heavy Spinner Kit" (SK-143) introduced in 1979 to overcome the chronic
cracking spinner problems Grumman American / Gulfstream American was
experiencing.



The new spinner system uses the "deep dish" backplate that fits between the
spacer and starter-ring gear assy. and is .050 aluminum. This leaves barley
more than 1/8" of only 4 drive bushings seating into the propeller spacer.
To make matters worse, the tension of the alternator belt cocks the ring
gear support off so it must be pushed back on the crankshaft flange to allow
any protrusion at all!



The maintenance manual instructs you to "hold the backplate back against the
pressure of the alternator belt and tape it to the cowling"! This really is
a poor procedure and it either damages the paint or lets go or both. The
solution is to have one person hold the backplate firmly in place while
another seats the prop and snugs up two bolts. In the 2nd STC installation
instructions I wrote (SA3326NM) I devoted a whole page to this procedure to
prevent the accidental improper installation and additionally certified the
option for replacing the two "very short" drive bushings with much longer
ones from the Piper PA28-180 (or all 6 of them if you wish) which prevents
this problem completely.



If you have an original McCauley, you have to remove it to comply with the
hub inspection AD every 200 hours. If you have a Sensenich, you will have
to remove it to pull the cowling for inspections and alternator or starter
maintenance unless you have a split nose cowling. If you do have the split
cowl, you really only need to remove the spinner to check the bolt torque
and re-safety them, so do not pull the propeller just because...!



If you still have a McCauley, you should seriously consider making the
investment in a Sensenich to not only get rid of the hub AD but the Yellow
Arc on the tachometer and associated vibration (which causes other damage)
and you will increase your performance noticeably and improve overall fuel
consumption. I KNOW it is about 4 grand these days for that propeller and
it is mandatory you have the heavy spinner (which you should already have
installed) because they are not getting any cheaper as time goes by. (They
increased $250.00 Jan. 1st.)



If you have the Sensenich installed on the original STC (SA1195NW) and want
to do the longer drive bushings, you can get the later STC (SA3326NM) and
just file a 337 for the paperwork change. The prop does not change at all.
OR... you can try for a Field Approval if you really want to. (I can supply
more details off line.)



Whatever you do, you may wish to print this out and force your mechanic to
read it before you next annual inspection or work requiring prop removal.
ALSO, this is applicable to AG-5B aircraft as they have the same short drive
bushings. Cheetah owners; you don't have short bushings so there is no
chance of screwing up installing the propellers, McCauley or Sensenich;



Ken Blackman

Air Mods N.W.

guru@airmodsnw.com

425-334-3030


 

[tony]

When you operate your aircraft under part 91 rules, which I think most of us here do, the pilot can not abdicate their responsibility of airworthiness to the mechanic. Part 91.3a states "The pilot in command of an aircraft is directly responsible for, and is the final authority as to, the operation of that aircraft."

So when you get your aircraft back from the shop it's the pilots responsibility to make sure the work was done right. If you blindly accept that your maintenance shop did the work right without checking it, you are a fool. When you get your aircraft back at annual it's the pilots job to make sure and double check all the ADs were complied with.

But in the real world I know, there are pilots and then there are appliance operators.......

[RJBrown]

There are many things a mechanic can do wrong that cannot be discovered without literally redoing every nut bolt and screw the AP/IA touched. I have seen things done wrong by mechanics almost every day as an auto shop owner. I have worked in the auto repair business for 40 years. I have owned and operated a repair shop for 33 years. One thing I have learned is mechanics make mistakes. To expect a pilot to catch every mistake a mechanic can make is unreasonable. An example of a hidden mistake would be the alternator drive gear installation in my Rocket. Someone at Continental assembled the engine that was installed when the Rocket conversion was initially done.

 Whoever this was forgot to bend the tabs that keep the bolts holding the alternator drive gear to the crankshaft from backing off. 80 hours later IFR out of Jackson Hole for Spokane the bolts came loose. The loose ring gear destroyed the alternator sending debris through the engine. The mistake was made in a TCM factory over a year before. That engine did not conform to it's certificate from day one and was technically never airworthy. The FAA did not come after me for flying a non airworthy plane. The responsibility for the non airworthy condition and liability for the damage belonged to TCM and it's AP/IA. My responsibility for airworthiness decisions began when the alternator failed and the mistake became apparent.

 The question for the pilot is: Would a reasonable person with reasonable diligence have been EXPECTED to discover the condition creating an un airworthy condition? Pilots are not APs. Pilots are not expected to be qualified to make a determination on every situation. That is why the AP/IA was trained and Certified to do his job. There are 2 very different standards otherwise every pilot must be an IA. 

[M016576]

There are many things a mechanic can do wrong that cannot be discovered without literally redoing every nut bolt and screw the AP/IA touched. I have seen things done wrong by mechanics almost every day as an auto shop owner. I have worked in the auto repair business for 40 years. I have owned and operated a repair shop for 33 years. One thing I have learned is mechanics make mistakes. To expect a pilot to catch every mistake a mechanic can make is unreasonable. An example of a hidden mistake would be the alternator drive gear installation in my Rocket. Someone at Continental assembled the engine that was installed when the Rocket conversion was initially done.

 Whoever this was forgot to bend the tabs that keep the bolts holding the alternator drive gear to the crankshaft from backing off. 80 hours later IFR out of Jackson Hole for Spokane the bolts came loose. The loose ring gear destroyed the alternator sending debris through the engine. The mistake was made in a TCM factory over a year before. That engine did not conform to it's certificate from day one and was technically never airworthy. The FAA did not come after me for flying a non airworthy plane. The responsibility for the non airworthy condition and liability for the damage belonged to TCM and it's AP/IA. My responsibility for airworthiness decisions began when the alternator failed and the mistake became apparent.

 The question for the pilot is: Would a reasonable person with reasonable diligence have been EXPECTED to discover the condition creating an un airworthy condition? Pilots are not APs. Pilots are not expected to be qualified to make a determination on every situation. That is why the AP/IA was trained and Certified to do his job. There are 2 very different standards otherwise every pilot must be an IA.

I agree with that statement, but...

Like in your example above: sometimes it's an A&P AI outside the "normal rotation" that can make a mistake years earlier in a spot that isn't normally accessed that be at fault. Like the continental A&P in your example. We like to think that all of us in the industry will always do our due diligence, and do our best to be professional and stand by our work, but the sad fact is that everyone makes mistakes. The A&P has a job to do. Fact. And he may or may not be liable, depending on what the issue is, but ultimately it's the pilots butt strapped into the aircraft, and unlike a military or commercial aircraft where it's easy to send the aircraft back to the shop, some owners opt to delay maintenance, or go past recommended overhaul cycles, because we can in part 91. In those cases, the pilot/owner should probably be held accountable, particularly if there was no sign of maintenance issues at the last inspection, if that's the reasonable smoking gun.

I'm not saying that this is the case in this particular issue, I'm just saying we don't really know what happened, or who's to blame: just that the pilot walked away... And as a pilot, it's one in the win column to walk away from something like this!

[Cody Stallings]

Let's talk About the propeller bolts.

I'm not trying to point any fingers, but. These 6 bolts are grossly neglected. We worry about out Cams an Crankshafts, an we worry about our propellers., But time after time the bolts go un inspected...... With our constant speed propellers, you get new mounting hardware every time it is Overhauled. When I overhaul a fixed pitch, I have to ask to have the bolts. Most of the time I don't get them though. Owner will say they are fine.

The reality is, most of the bolts that are securing the fixed pitch propeller to a flange, are the original bolts that came with the plane.

I removed a propeller from a Cessna 177 that had a break away tourqe of 90ft.lb..... Factory spec is 28-30ft.lb. Thes bolts are over tourqed, stretched an corroded. As long as they are in one piece, they get re-installed.

These bolts need to be Mag tested, checked for stretch, an replated.... Your propeller is only as good as what's holding it on. Just my 2 pennies