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SERVICE BULLETIN 2000-001B
TARVER PROPELLERS, LLC Hangar C-4
This Service Bulletin replaces Service
Bulletin 2000-001A dated
Propeller Blade Inspection
A.
Background: There is concern that a potential problem may
exist in propeller blades of the models listed below. Many of these propellers have a manufacturing
date as early as 1946. The concern stems
from the obvious possibility that there can be detectable deterioration of the
blade retention system due to moisture intrusion or vibration. Neither of these problems are specific to
older propellers. Obviously the older
the propeller the more opportunity there is for this condition to exist. The track record of these propeller blades,
during the past years since 1946 indicate clearly that there is no unusual
problem that has surfaced which would require drastic or emergency action. There is however, a better way to verify the
airworthiness of these propeller blades.
Past inspection criteria is in need of being updated, specifically in
the shank retention area. This service
bulletin addresses that need. FAR 35.35
specifically states that a propeller shall have a blade retention safety factor
of two. The retention system for these
propeller blades have been tested and verified to have a safety factor of 4.2
or more. Thus it appears that this is
the strongest "link in the chain".
This does not imply that it should be neglected. Moisture Intrusion. These laminated wood propeller blades were
assembled using a wood preservative. The
material is a proprietary liquid by the name of Nelsonite. Deterioration of the wood in these propellers
is very rare. The Tarver Propeller
company has found rusted retention screws in these blades yet the wood had no decay. Some of the suspected wood was analyzed by
the Forest Products Laboratory, a branch of the U. S. Department of Agriculture,
and was found to have no decay even though it was stained by iron oxide. Vibration. Vibration, whether caused by an unbalanced
propeller or engine is a matter that must be corrected. Vibration causes resonant nodes at various
frequencies that are harmonically related to engine/propeller rpm which in turn
can be aggravated by the dynamic loads on the propeller. This condition causes excessive stress on the
blade retention system as well as the hub and of course the engine. Static balance of a propeller is valid. If the propeller is properly statically
balanced, engine unbalance, if it exists, should be corrected, but not by
unbalancing the propeller. B. Requirements: This Service Bulletin addresses two
requirements. Inspection following the
criteria provided in this bulletin will assist in bringing a propeller, which
is in an unknown condition of airworthiness, into a known condition of
airworthiness. First, the Service
Bulletin provides inspection criteria for assembled propellers to aid in
determining the integrity of the blade attachment area. The second is the provision of more reliable
inspection criteria for inspection of propeller blades at an appropriately
rated propeller repair station. Airworthiness
Condition. Clearly there are situations
in the field, for various reasons, where the owner/operator does not know the
airworthiness condition of his propeller.
An operator should not continue using a propeller that is in an unknown
condition. After compliance with this
service bulletin and associated maintenance manuals, the owner/operator will
have a propeller of which the condition is established. Inspection
Criteria. In the past, the inspection
criteria for the blade retention system consisted of verifying that each of the
lag screws in the shank will accept 150 in/lb of torque without breaking or
stripping the threads in the wood.
Passing this test does not entirely verify the integrity of the screw.
The Tarver Propeller company has found that a screw that passes this torque
test can have enough rust on the threads that makes the part unairworthy. Many screws have been held in place so tight
with rust that it is impossible to back out the screw without twisting it in
two. Therefore a more thorough
inspection method is detailed below which eliminates this ambiguity. C. Effectivity: This service bulletin is applicable to all
Aeromatic propellers models F200, F200‑H, 220, 220‑1, 220H. The Aeromatic models listed above were
originally manufactured by Koppers, then Univair, then South 80, then Brown
Propellers, LTD. Tarver Propellers, LLC
is now the TC holder of the above model propellers and blades. D. Compliance Requirements: If the owner/operator has one of the above
propellers which is in an unknown condition, then Tarver Propellers, LLC
considers compliance with this service bulletin to be mandatory prior to
putting it into service or continuing service beyond the times listed below. E. Description: This Service Bulletin provides information
for visual inspection of all the above wood propeller blades for unsafe
condition due to corroded lag screws and decay (dry rot) of the wood at the
blade leading edge and at the interface of the blade and ferrule. F. Instructions For those propellers that are judged to be in
need of this inspection, the following shall be performed: Part I: Initial
Inspection for Blade Looseness between the Blade Shank and Metal Ferrule. 1) Prior to further flight, visually inspect
each propeller blade for mounting security by pushing and pulling (with as much force that
a man can apply with one hand on the tip) of the blade in a fore and aft
motion. While exerting these forces,
play can be detected by placing your thumb at the point where the wood blade
enters the ferrule. Perform this
inspection on both blades. If any motion
is detected the propeller is unairworthy.
2)
This
test should be a part of the airplane preflight inspection. If no looseness (play) is detected, the
airplane may continue operation until compliance to Part II of this Service
Bulletin. Part
II: Shop Inspection. The Following
Procedures are to be used in Conjunction with the Koppers Aeromatic Repair
Manual and Shop Inspection Procedures for Blade Repair 1) If any
looseness (play) is detected the propeller
must be removed and forwarded to an appropriately rated propeller repair
station for disassembly and inspection. a) The blades must be removed
from the hub and inspected for broken, missing, or the presence of unapproved
lag screws. b) Each lag screw shall be removed and inspected
for corrosion. Refer to note 1. c) The ferrule shall be removed from the blade
in order to gain unobstructed access to the wood for inspection. The ferrule may be reconditioned as necessary
and reused. Refer to note 2. d) The blade shank perimeter screw holes and
balance weight holes shall be inspected for wood decay, cracks or delamination. Refer to note 3. e) The ferrule shall be reinstalled on the shank
in the same clock position as it was prior to removal. Refer to note 4. f) If the propeller blade is finished with
plastic coating, the interface where the ferrule meets the coating shall be
sealed using spot putty or plastic patch or a combination of both depending on
how much area has to be covered. g) If the blade does not have plastic coating,
then spot putty may be used to reseal the area.
The lag screws shall be reinstalled and torqued before the seal has
dried. h) The lag screws shall be dipped in Nelsonite,
installed into a screw hole and torqued to 150 in/lb in addition to running
torque. See Note 5. i) The metal leading edge/tipping shall be
inspected in accordance with Service Bulletin 25C. Note 1. All lag screws shall be removed using reverse
torque. If the screw breaks during reverse torque it is
a strong indication of excessive corrosion.
All screws shall meet the installation criteria of Part II, 1. h. Lag screws that are to be installed shall
bear no signs of rust. Note 2. The ferrule may be cleaned of surface
corrosion and corrosion proofed by application of zinc chromate primer. Deep corrosion pits anywhere on the ferrule
is criteria for rejection. Note 3. Inspect
the wood using a sharp tool (such as an awl) that can be used to probe the wood
in various places in and around the exposed shank. The screw hole threads shall be inspected for
damage with a borescope. Look for any
visible cracks in the wood in the screw holes and any obvious gross damage to
the threads. Small cracks in no more
than 3 screw holes and if, later, the screw will meet the requirements of Part II,
1. h, then this is not criteria for rejection of the blade. Cracks that connect two or more screw holes are
cause for rejection of the blade. Most
blades contain some amount of lead wool in the center of the balance hole. This lead may cause a whitish stain on the
wood near the lead and is not criteria for rejection unless the wood is found
to be soft based upon the probing described above. Various degrees of brown stain will virtually
always be present on the wood and is not the deciding factor for rejection. Note 4. The ferrule will have a small hole drilled in
the side wall and a matching hole will be found in the shank of the blade. Be sure that these holes match up when
reinstalling the ferrule. Note 5. The ferrule shall be reassembled onto the
blade shank. Screws of the same length
as were removed shall be used to reinstall the ferrule. After all screws have seated against the
ferrule, all of them shall be re-torqued at least three times. This assures a uniform strain among the
screws. THIS IS IMPORTANT! Part III. Repetitive
Inspections The inspection
detailed in Part I should be performed any time the condition of the propeller
blades becomes unknown or when any looseness of a blade is detected as detailed
in Part I "Prior to Further Flight". Summary: This inspection
requires that the propeller be disassembled, reassembled, the blade angles
checked, balanced, pressure checking the hub, and adding lubricant. The estimated time to perform this, assuming
no repairs or parts are required, is 8 to 12 hours. This bulletin may be
complied with by an appropriately rated propeller repair station or by Tarver
Propellers, LLC. Telephone and FAX 775-423-0378 www.aeromatic.com
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