Information Letters

INFORMATION LETTER #1996-1

Sikorsky S-55 and S-58 Main Rotor Blades

Some operators are having trouble or have had trouble balancing Orlando Blade Technologies (“OBT”) overhauled main rotor blades. This problem seems especially severe when running OBT blades with Sikorsky, Military or ABS BIMed blades. During our investigations into this problem we discovered that when OBT BIMed the blade it occasionally decided to remove some weight from inside the spar. A simple test is to take a strong magnet and run it along the spar just aft of the leading edge, the pull of the magnet on the steel balance weights can be felt. When measuring from the tip end of the spar there should be 235” of weights installed. OBT typically removed 24” of additional weight during its BIM installation procedure. Total weight removed is from about 2.2 lbs. to 4.4 lbs. This was then compensated for by increasing the amount of weight in the tip end of the blade in the span-wise balance position. Thus, the blade has less weight and also is cordwise out of balance.

Please be aware that when installing a blade that was BIMed by Sikorsky, the Military, or ABS across from an OBT BIMed blade you may experience difficulty in your track and balance exercises. Usually you can tell if OBT BIMed the blade by inspecting the log card of the blade. It should have signed off the installation of the BIM system, “installation in accordance with Sikorsky Service Bulletin 58B15-4M.”

If you are currently running 4 OBT BIMed blades together quite possibly you won’t notice this until you swap one or more blades with blades not converted by OBT. Then you will probably blame the new blade(s) for not flying with the others. Also, should you send in a blade, we will have to correct this as it is not in compliance with the type certificate or the manufacturers drawings.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #1997-1

Sikorsky S-55, S-58 and S-61Main Rotor Blades

SPAR CORROSION

The blades installed on aging aircraft will be a concern for operators.

All operators shop for the best price and many of the replacement blades purchased may visually appear to be in good condition. Some of these replacement blades end up in our shop for a complete inspection while others are installed on helicopters as serviceable.

There are several conditions we think all operators need to be aware of.

When inspecting blades for possible purchase, note the way that they are stored. The reusable aluminum containers that most surplus blades are stored in need very careful scrutiny. Make sure the B.I.M. system is still intact and that it has a serviceable indicator installed with a good indication. As most inspectors know, this is a very critical system in these blades and it does work very well. If the blade has been properly serviced, the spar has been purged with nitrogen which is used to eliminate moisture, which is critical in a closed system such as this. These blades have nothing more than a thin coat of primer on the inside of the spar and some of the primer deteriorates with time and flakes off which leaves the spar bare in some areas. This can be a very deleterious situation if not addressed right away. Many of these blades can be salvaged if the damage is not left until the last minute.

The above scenario is one of the reasons we X-ray the main spar which will show any internal corrosion. We also X-ray the pockets for the same reason, to view the presence of internal corrosion or water. If water has been absorbed in the pockets, it will sit on the spar back wall and will render the blade unserviceable. This problem of water contamination in the pockets will only occur on the S-55 and S-58 main rotor blades with honeycomb pockets installed, while the S-61 and S-64 still have a definite problem with internal corrosion and corrosion on the back wall. Many of the blades we have seen have the X-ray stamp on the spar, but this inspection may have been completed many years ago. We recommend that a current X-ray be completed on any surplus blade that is planned to be put into service.

The next area of concern we would like to address are the pocket seals. The seals are fabricated from fully encapsulated nitrated foam. These foam seals are then sealed with a fuel resistant coating prior to installation. If the seals were installed years ago some may have deteriorated to such a state that they do nothing more than trap moisture in these areas. If this problem is not rectified in a timely manner, corrosion will soon scrap your blade. So make sure your pocket joints are properly sealed.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #1997-2

Sikorsky S-55, S-58, S-61 and S-64 Main Rotor Blades

CRACK PROPAGATION

We have seen several blades that have very serious problems. This blade was operated by a logging company that has very high rates of turns per hour and with an extremely high utilization under heavy loading.

These cracks were all found on the bottom side of the blade at the cuff attachment point and all started at one of the mount bolt holes. The cuff attachment point is a very sensitive location on the blade as the required fit between the cuff, spar and bolt is reamed to a very tight tolerance.

The blade shown was removed from service due to the daily B.I.M. inspection. The indicator showed red and subsequently the blade was removed from service. This blade was then sent to another blade shop. It was diagnosed as a tip dam leak and repaired at that time. The blade was then returned to the customer and this problem was again experienced and the same diagnoses was rendered to the customer. The blade was then reinstalled on the helicopter and lasted about 7 hours and again the indicator went red. At that point the blade was shipped to ABS. We then utilized our helium leak detection system and immediately located the problem, the cuff leak at several bolt holes. The cuff was removed, and the true problem was then located.

This situation was quite a shock to all our staff. The customer authorized us to destroy the blade, so we cut the inboard end off the spar and totally reassembled the cuff system. This allowed us to use this portion of the blade for test purposes. We are working with a specialty testing laboratory to devise a method to detect this type of problem prior to failure without disassembling the blade. Removing and reinstalling the cuff end of the blade gets to be very costly and we will do our best to find a method to detect this problem without tearing the blade apart.

The lesson here is the B.I.M. system that Sikorsky designed and installed on its blades works very well if appropriately maintained.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2000-1

Sikorsky S-61/H3/Agusta AS-61/Westland Sea King/Commando

POCKET CORROSION

Upon inspection of 40 main rotor blades manufactured by Agusta, Sikorsky and Westland, we isolated the following problem:

1. We recently completed inspection on 10 each Westland manufactured main rotor blades part number, WD4529-00002-047. By visual inspection and X-ray, we found that 82 pockets out of 230 had severe internal corrosion. Most of the corrosion was on the ribs that support the skin.

The pockets are manufactured in several pieces: the skin, internal ribs and the back wall. There are a number of pocket configurations used on this blade, some have five internal support ribs and the others have eight ribs. The pocket skin, ribs, back wall and adhesive are then assembled in an alignment fixture and heated to cure the adhesive. Prior to assembly, all parts are heat treated for strength and anodized for corrosion resistance.

The Westland manufactured pockets we inspected revealed severe corrosion present on an abnormal amount of support ribs. Some interior skin had corrosion present, but in small amounts, and the back wall showed no corrosion problem. This problem may have stemmed from the process used to manufacture the ribs or in the anodize plating process used.

In field operations many of these pockets may be found by inspecting each pocket for rib integrity by applying external pressure on the pocket skin, by applying light hand pressure to determine if the ribs are structurally sound.

2. Aviation Blade Services received 10 each Agusta main rotor blades that were stored in a barge in excess of 100 days. We found an average of 12 pockets per assembly of Agusta manufactured rotor blades that were replaced due to pocket internal and external corrosion. Out of the 10 blades inspected, 4 were removed from service due to spar corrosion beyond allowable limits and 6 were repaired and returned to the customer. With proper storage, handling and shipping the potential for this problem would have been minimized.

3. Over the past 5 years we have replaced a very small number of Sikorsky manufactured pockets due to internal corrosion.

We cannot overly stress the need to properly maintain, store, handle and ship your rotor blades as repairs can become quite expensive. Although the severe corrosion we have repaired has been isolated to the Westland manufactured pocket assemblies and the Augusta blades that were improperly stored, this problem will continue to occur and increase your operational cost if the proper storage and handling rotor blades is not addressed.

The above photo is just one example of a corroded pocket removed from a Westland Sea King main rotor blade. Aviation Blade Services has replaced many that have been corroded to a greater degree. This corroded pocket was found during a visual inspection but many that have not reached this stage of corrosion can only be found by means of X-ray or fluoroscope. Approximately 80% of the pockets replaced on a Westland manufactured blade will be due to corrosion inside the pocket.

Sikorsky and Augusta manufactured pockets have not experienced this specific problem. If they have been replaced due to corrosion it was mostly exhibited on the skin surface but very seldom on the internal ribs. If the ribs are corroded on the Sikorsky or Augusta rotor blade there has always been additional corrosion found throughout the pocket surfaces.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2002-1

Sikorsky S-61/H-3 Tail Rotor Blade Corrosion

Aviation Blade Services has received tail rotor blades part number S6117-30101 and S6117-30201 from various operators for repair. This blade has an additional balance weight system in under the root-end filler to provide an additional cord-wise balance means. The root-end filler is still manufactured from balsa wood and sealed with clear lacquer.

Several blades have been received with the balsa insert sealed with structural adhesive, which made inspection in the field almost impossible. When this area of the blade is inspected finger pressure is applied to the filler to determine if it is soft, if so you replace this filler I/A/W your Sikorsky maintenance manual, see below Figure 4-20. The filler is always hard to the touch if sealed with structural adhesive but the adhesive will dis-bond from the sides of the root-channel allowing moisture to enter the cavity.

As seen in the picture below the balsa filler holds moisture in this area and now there may be corrosion. The blade in the illustration had to have the pocket, strap and root channel replaced. If this problem had not been addressed the blade may have to have been scrapped due to the corrosion damage to the spar.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection.

Most tail rotor blades where the balsa filler has deteriorated and have moisture present take additional labor to repair and static balance due to the corrosion of the balance weight retaining bolt. Many of these blades will have to have the screw drilled out with out damaging the nut plate. The nut plate is installed in the root channel prior to installing the assembly in the blade. In most circumstances to replace the root channel the pocket will need replacing also.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2002-2

Sikorsky S-58/S-58T and S-61/H-3 Tail Rotor Blade Erosion

Aviation Blade Services has received a number of tail rotor blades with tip cap and abrasion strip damage. Upon detailed inspection we found that the tip cap mount landing had been severely eroded, as illustrated in the following picture. This damage is the reason many blades have been removed from service; they were determined to be SCRAP. Sikorsky only allows repairs to this area if the erosion has not exceeded .125”, which in many tail rotor blades is the case.

Aviation Blade Services received authorization to increase the amount of repairable erosion thus saving numerous blades. The main point to operators is, maintain your abrasion strip and tip cap. Many blades exhibit this damage to some degree. The cause of tip caps which are severely eroded or improperly fit is severe erosion to the abrasion strip. If the tip cap and abrasion strip do not make firm contact with each other in this area there will be a problem. Some of the blades received at ABS came in presumed repairable condition but after removing the tip cap and abrasion strip the more severe problem was uncovered.

The picture below is a tail blade purchased by an operator and installed on the aircraft in ‘as is’ condition. When the abrasion strip was found to be voided ABS was contracted for the repairs. The previous owner had replaced the tip cap and did a good job, but did not address the erosion thus the hidden damage was covered up.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2003-1

Operator Painted Blades

Recently we received a number of main rotor blades sent to Aviation Blade Services with balance problems. These blades were for the S-58 and S-61 helicopters. Apparently these operators thought they were properly maintaining their helicopter by painting the blades, however other problems were created by doing this.

By repainting the tops of the blade with a polyurethane paint approximately 1 to 2 mils of paint was added to the top or approximately 1 to 2 lbs of weight to the blade (polyurethane is a high solids paint and weighs more than the original lacquer finish). Most operators apply the new topcoat directly to the blade surface and not remove any of the old paint. On a Sikorsky S-58 main rotor blade with a cord dimension of 16.5 inches and an S-61 blade with 18.5 inch cord, your cord wise center of gravity is approximately 4.6 inches from the leading edge. Considering the amount of paint applied to the blade, most of the paint is aft of the center of gravity thus three times more weight in paint is aft. You don’t really know what condition the balance of the blade is in before you start. As repairs are completed on blades which have been in operation for years such as field repairs and paint touch ups, the weight of the blade is increased and the cord wise balance changes. One or more blades could be heavy to start with, thus when blades are painted any out of balance problem may be exacerbated.

While such blades are technically out of balance they may fly together as a set if painted at the same time by the same painter and with the same product. However, the problem that will arise in the future is when one of the blades needs to be replaced. The new blade is not going to fly very well with the originals, as it is probably up to 2 lbs lighter, resulting in an aircraft that is rough in the air and also will cause excess wear and tear on all of the aircraft, especially the head, flight controls and airframe.

Some of the items that will suffer from blades being out of dynamic balance:

1) Rod ends and bearings in the main rotor head

2) Rotating star bearing

3) On a helicopter that does not provide for rotor head balance, out of dynamic balance blades can cause lots of problems that may not be apparent at that time but will eventually surface.

A simple check of the condition of your main blades is to observe what happens to the blade track when you turn off the primary servos during your flight checks. Do they stay together as when both systems are operating, or do they separate and seek their own track path? The design of the sloppy links on the primary servos allows for the blade to run where it needs to when the primaries are shut off, not where you force it to run. If you have ever lost the primary system in flight and the helicopter was hard to fly or land, you will understand the reason for properly balanced blades. You should notice no appreciable handling difference with the primary system off, on the ground or in the air.

This information letter has been provided to call operators’ attention to a potential problem that needs to be considered before starting a painting process. In spite of the fact that blades seem to be robust and require very little maintenance, they are in fact operationally delicate. By paying attention to the static balance of the blades operators will see significantly lower maintenance and vibration in the area of the rotor head, flight controls and airframe.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2005-1

Media Blasting of Paint on Sikorsky Rotor Blades

In recent years media blasting of aircraft parts to remove old paint has become an ever-increasing method as a substitute for chemical paint stripping.

An operator should be aware of the potential consequences if he wishes to utilize this method of paint removal.

First, the OEM’s specs and procedures should be reviewed to determine the process and which parts are approved for media blast paint removal. At this time Sikorsky does not approve of any media blast system for use on its metal rotor blades.

Second, if regardless of OEM specs an operator is determined to use a media blast system, caution should be taken. The use of media equipment in inexperienced hands can have serious and costly consequences. The below picture illustrates what may happen.

The two S-61 blades shown below were media blasted by an inexperienced individual who cost his owner in excess of US$22,000.00 for pocket replacement repairs. The pocket skin on both the main rotor and tail rotor blade is made from .012” aluminum material. By aggressively blasting in a single area too long the material will stretch between the ribs rendering this undesirable look and an unserviceable rotor blade.

Third, the owner/operator also needs to review whether or not its repair station authorization extends to cover rotor blade type of repairs. Rotor blades are not lumped in with blanket component type authorities. The operator or his employees could in fact be opening the company up to an unanticipated liability.

The reason Sikorsky does not allow entire rotor blade paint stripping and repainting in either the Maintenance Manual or the Structural Repair Manual is because the owner/operator does not have the proper authorizations, balance equipment, procedures, tooling and personnel to completely strip, repair, refinish and rebalance the blade back to a known master. The balancing of the blade is as critical to a rotor blade as the gear setting is to a gearbox. Sikorsky only allows touch up type of repairs to the painted surface.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2005-2

Use of Cherry Max Rivets to Install T/R Tip Caps

This information Letter pertains to the Sikorsky S-58/H-34 p/n S1615-30101 t/r blade & S-61/H-3 p/n S6117-30101 & 61170-30201 t/r blade tip caps.

Every year Aviation Blade Services receives several S-58 or S-61 tail rotor blades that have had the tip cap repaired or replaced using Cherry Max rivets. These rivets are not the proper rivets called for in the parts manual or SRM for use to secure a tip cap. While these rivets work they are intended to be a permanent installation and the tip cap is not a permanent installation.

The Cherry Max rivet uses a monel stem in an aluminum sleeve. The problem is in the removal of the rivet. In order to drill the rivet out the stem must be ground and lock collar away to be able to drill the rivet. If the tip cap is not damaged during the grinding, then the rivet usually spins during the drilling thereby enlarging the hole.

The proper rivet is an all aluminum rivet, sleeve, stem and lock collar. The current part number is NAS1921B04- (which superseded the 100V4 series). The NAS 1921 rivets are generally easier to remove with less damage to the tip cap or blade.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.

INFORMATION LETTER #2006-1

So You Think You Found a Good Deal on a Rotor Blade?

We have met operators who have made ‘special deals’ on the purchase of rotor blades, especially for the S-58. They buy the blade based on some “it looks good to me” or “I been in the business for 30 years and I say it’s OK” kind of certification. The S-58 blades have been around a long time without much attention having been given to rust or corrosion issues. Operators may believe if the BIM is still yellow it must be a good blade.

By simply looking at the outside of the blade one has absolutely no possible idea of what the condition of the inside of the spar is like.

Most of the blades on the market today have not had a shop visit for approximately 30 years and were likely repaired in the early to mid 1970’s. Some blades go back even further. Shop visits can be costly, but it is not correct that the condition of a blade may be determined by only viewing the exterior. It cannot be stressed enough that without a thorough internal inspection lives will be at risk.

Aviation Blade Services has been and will be continuing to remove the cuffs from the spar on almost all S-55, S-58, S-64 main rotor blades in order to ensure that corrosion and rust are not hidden from sight.

For more information contact Paul Bolton at (407) 846-6780.

This notice is for information purposes only and does not condemn any blade without a more detailed inspection of the blades.