Clarification on Supervising a Non-Certificated Person Working on Aircraft

Customers have asked me if they can perform work on their aircraft under my supervision and if I needed to be there to direct them while doing the work. They have told me that other mechanics have allowed them to do work while that mechanic was not present. They also said that they could just send that mechanic a picture of the finished work they had completed and that the mechanic would then sign the work off in their log books. They went on to state that their mechanic had worked with them in the past and trusted their work.

I have researched the Internet and the FAA’s Chief Counsel database looking for a Legal Interpretation of this regulation, without finding any worthwhile results.

This is addressed under FAR 43.3(d). 

43.3 (d) A person working under the supervision of a holder of a mechanic or repairman certificate may perform the maintenance, preventive maintenance, and alterations that his supervisor is authorized to perform, if the supervisor personally observes the work being done to the extent necessary to ensure that it is being done properly and if the supervisor is readily available, in person, for consultation. However, this paragraph does not authorize the performance of any inspection required by Part 91 or Part 125 of this chapter or any inspection performed after a major repair or alteration.

Here is my my interpretation of this regulation

There are three parts to this regulation that must be met in order for the supervising mechanic to be in compliance.

Part 1 reads:

if the supervisor personally observes the work being done

To personally observe the work is self explanatory. It means the supervisor himself and no other person.

Part 2 reads:

to the extent necessary to ensure that it is being done properly

This is a bit more vague and somewhat subjective. It means that if the work performed consists of multiple tasks or steps (which most work consists of), then the supervisor must personally observe each of those steps that make up the entire process from start to finish. The reasoning behind this is that once a person has completed a step and moved to the next step, the prior step cannot be observed (in most cases) by the supervisor to ensure that it is being done properly.

If the supervisor can observe the finished work and determine, by observation alone, that the work was done properly, then this would satisfy the requirements of the regulation. IE a person assembles a simple piece by drilling holes and installing a few rivets. The supervisor inspects the piece and verifies that it meets the dimensions and that the rivets are properly installed and the correct type/size. By this inspection he can satisfy the requirements of the regulation.

Another example might be when a person installs a propeller. If the supervisor only personally observes the finished work by inspection of the propeller after it has been installed and safety wired, then he could not, to the extent necessary, ensure that it (the installation of the propeller) was done properly. The reason that this would not satisfy the requirements of the regulation is that there are multiple steps to installing a propeller, some of which are critical to the safety of the finished process.

1. Inspection of the crankshaft flange, thread inserts and attaching bolts,

2. Correct indexing of the propeller to crankshaft flange (if the propeller can attach in more then one position)

3. Torque requirements of the attaching hardware (dry or lubricated threads, stretch fit, degrees to rotate, etc)

4. Torque setting and correct procedure to apply torque

5. Torque wrench used.

Inspection of the completed work alone would not reveal that the above 5 steps were done properly and therefore would not satisfy the requirements of the regulation.

Part 3 reads:

if the supervisor is readily available, in person, for consultation

This is self explanatory. The supervisor must be available, in person. The current definition of in person is:

Merriam-Webster Dictionary: “in one’s bodily presence “

Cambridge Dictionary: by meeting with someone rather than talking on the phone, emailing, or writing to the person. This basically means being physically present.

In summary. The supervisor must observe those steps during the work being performed that cannot be observed by the finished work alone, and he must be physically present and readily available (on site) while the work is being performed. Can the supervisor meet the requirements of the regulation without being physically present? No, he cannot. Can the Supervisor inspect just the finished work that was performed? Not likely, unless the task consists of only a few simple steps.

If a mechanic trusts another persons work, does this entitle that person to perform work that would normally require a certified mechanic to perform? Does this “trust” alleviate the Supervisor’s responsibly from complying with the above three requirements of the regulation? The answer is no to both of these. There is nothing within this regulation that allows the Supervisor to waive his responsibilities just because he “trusts" another persons work.

Rolls Royce 250 Series Gas Turbine Engine Failure Case Study

Introduction

The following article is based on an investigation and analysis of an aircraft accident of one Hughes 369D helicopter (Hughes 500D) equipped with one Rolls-Royce 250-C20B gas turbine engine. I was retained by the defense council as an Expert Witness in this case which resulted in a fatality. Information that was used to support these conclusions are listed at the end of this article. A physical and lab examination was performed on the accident engine components at a metallurgy forensic lab. Note that names, dates, document numbers, etc. have been changed and/or X'ed out to protect the privacy of the involved parties.

Engine Failure

The helicopter experienced a sudden and total engine failure while stationary in an out-of-ground-effect hover at approximately 120 feet above the ground. The pilot was performing an inspection of power lines and their support towers at the time of the engine failure. This sudden failure occurred without any warning and resulted in a total loss of power. A post-accident engine investigation performed by Rolls-Royce (RR), and overseen by the FAA, concluded that the cause of the failure was due to blade separation of the 2^nd stage gas producer turbine wheel. It was determined that the blade separation was caused by high cycle fatigue (HCF) and over-temperature thermal stress. The HCF is attributed to a localized over-temperature condition (hot spot) that was evident by an area of complete burn-through to a section of the 1^st stage turbine nozzle assembly around the 11 o'clock position. There was also evidence of an uneven flame pattern indicated by non-uniform discoloration of the combustion liner. This uneven flame distribution, which caused the thermal damage, was the direct result of a streaking fuel nozzle. These conclusions of the turbine failure were corroborated by a very highly regarded independent Expert specializing in engine metallurgy failure analysis.

Fuel Nozzle Discussion

The fuel nozzle streaking was caused by carbon build-up near the nozzle tip which disrupted the atomized spray pattern cone. This disruption caused a stream of non-atomized raw liquid fuel to enter the combustor. This concentration of raw fuel burned in a localized area near the 11 o'clock position of the 1^st stage nozzle at temperatures in excess of the safe operating limits of the combustion section (hot section). This localized over-temperature condition was undetected and was allowed to continue to the point that the internal components of the engine hot section were permanently damaged resulting in failure.

The fuel nozzle streaking had developed sometime within the last 235 flight hours and had continued to streak without detection. This condition went undetected due to the fact that the only reliable method to determine that a fuel nozzle is functioning properly is to perform the fuel nozzle maintenance per the RR maintenance manual, which had not been accomplished.

Maintenance Requirements

The engine manufacturer (RR) has developed and refined a maintenance program based on the production of over 30,000 RR 250 series engines with a production run spanning 50 years. The 250 series engine has accumulated an operating history of over 200 million fleet flight hours to date. This maintenance program contains a detailed checklist in the RR 250-C20 Series Operation and Maintenance Manual (OMM), chapter 72-00-00, Table 602 titled, “Scheduled Inspections.” The RR 250-C20 Series OMM states, “Scheduled inspections are made at periodic intervals in an effort to prevent engine malfunction and serve in the role of preventative maintenance for the engine.” This inspection checklist details the actions required to be performed during each inspection interval. One of the items contained within the “100 Hour Inspection” section is 21.A and states, “Remove, inspect and clean the fuel nozzle,” and, “NOTE: Operators may find it necessary to inspect and clean the fuel nozzle more often depending on past experience or operating conditions.”

This engine utilizes only one fuel nozzle and therefore it is an extremely critical component. The 100 hour inspection requirement of the fuel nozzle has developed over the years through field experience and is considered the absolute maximum number of flight hours allowable between inspections. The OMM chapter 73-10-03 states “NOTE: Due to variation in fuels and operating conditions, fuel nozzle cleaning may be necessary at more frequent intervals then stated in Table 602, 72-00-00, Engine – Inspection/Check, to maintain proper combustion flame pattern.” The critically important nature of this fuel nozzle maintenance cannot be overstated.

Maintenance Records Investigation

The accident helicopter was operated and maintained by (name withheld, hereafter referred to as the Company). A thorough investigation of the helicopter's maintenance records revealed that the 100 hour fuel nozzle maintenance was not being performed as required by the engine manufacturer. The records indicate that the last documented fuel nozzle maintenance was performed 234.9 flight hours prior to the accident. The records also indicate that over the last 1097 flight hours, the fuel nozzle maintenance had only been performed two times (ref. Figure 1). RR requires that the fuel nozzle be removed, inspected and cleaned at intervals not to exceed 100 hours and that the operator should consider even shorter time intervals depending on their past experience or operating conditions.

There is considerable evidence contained in the Company maintenance records, wherein the information contained in one record conflicts with another record of the same inspection and date. Also, the checklists that were used to perform maintenance were inconsistent. After examining the records of 11 of the last 100 hour inspections, dating over a one year period, it was apparent that the maintenance personnel had been using incorrect/outdated checklists during most of those inspections (ref. Figure 1). Only on two occasions had the correct checklists been used. The correct checklist that should have been used is contained in the OMM chapter 72-00-00 Table 602 with a revision date of June 1, 2004 and required that the fuel nozzle be maintained each 100 hours. The use of any other prior dated checklist after the effective date of the June 1, 2004 checklist revision, would not be approved or acceptable.

Multiple maintenance records contained conflicting information. For example, on some of the Company forms titled “Approval for the Return to Service,” the maintenance personnel signed off that a specific inspection was complied with. However, on the checklist used to perform that maintenance, that specific inspection item is not shown to have been complied with. Therefore these two records are in conflict with one another.

Another issue is that it is unclear as to what type of maintenance inspection program the Company was actually using to comply with the airworthiness requirement set forth by the FARs. The records reviewed indicated that they were using the Manufacturer's Inspection Program including the checklists contained within those programs. The Company's “Approval for Return to Service” form contains a printed statement as follows, “This aircraft is in a 100 Hour / Annual / Manufacturer's Inspection Program CFR 43.15 (b), (c)(1)(3).” However, a letter addressed to the NTSB from a Company representative states, “the Company, at that time, was not performing its maintenance under that program, nor was it required to.” This was in reference to the manufacturer's program. He signed with the title, Director of Safety/Regulatory Compliance. His statement is in direct conflict with the Company's maintenance records.

The fact that the Company did not adhere to the RR maintenance program, used outdated documentation to perform maintenance, and that their own maintenance records are in conflict with each other, are all indicators that the Company's maintenance was substandard, negligent, inconsistent with industry standards, and compromised the safety of flight and rendered it unreasonably dangerous. The Company's maintenance records reflect a standard of care that breached the aviation industry's level of acceptance, manufacturer's specifications and violated applicable FARs.

100 Hour Inspection Maintenance Records

Figure 1

A	B	C	D	E
AFTT	Date	Fuel Nozzle Maint. per Checklist	Fuel Nozzle Maint. per RTS Form	Checklist Used
10816.3	05/28/07	Accident
10773.6	05/13/07	No	No	Old
10670.9	04/12/07	No	No	Old
10581.4	02/25/07	Yes	Yes	New
10478.3	01/11/07	No Record	Yes	No Record
10381.1	12/12/06	No	Yes	Old
10283.2	11/11/06	No Record	Yes	No Record
10200.0	10/13/06	No	Yes	Old
10103.4	09/17/06	No	Yes	Old
10005.9	08/22/06	Yes	Yes	New
9905.8	08/03/06	No	Yes	Old
9809.1	07/17/06	No	Yes	Old
9719.7	06/21/06	Overhauled Fuel Nozzle Installed by the Company

NOTES:

A. Total flight hours at time of inspection.

C. Documented fuel nozzle maintenance recorded on the RR checklist.

D. Documented fuel nozzle maintenance recorded on the Company's return to service form.

E. Checklist used to perform the inspection. This is contained in the RR OMM Table 602. The new Table 602 has a revision date of June 1, 2004.

Columns C & D show conflicting information.

Column E shows outdated checklist being used.

Maintenance Considerations

Fuel nozzle removal, inspection and cleaning is the only way to detect a condition that could lead to or cause fuel streaking and it is critical since there is no other way to determine a localized over-temperature condition. An early detection of a streaking fuel nozzle can preclude irreversible internal engine component damage. Had the fuel nozzle maintenance been performed in accordance with RR procedures, the malfunctioning fuel nozzle would have been discovered and the problem corrected. It is highly likely that an early discovery of such a condition would have prevented hot section damage and turbine failure. This discovery could have alerted the operator that it would be prudent to perform a simple borescope inspection of the hot section to determine if any signs of thermal stress/damage had occurred due to the streaking fuel nozzle. If any signs of thermal damage were discovered at this early stage, the procedure would be to perform a hot section inspection in accordance with RR instructions to determine the extent of the damage prior to further flight. This procedure would prevent an in-flight engine failure due to thermal damage.

The Company's Operations and Risk Assessment

The Company performs aerial power line inspection, maintenance and construction for the electrical utility industry utilizing helicopters. Typical day-to-day operations performed by the Company

require that the helicopter and its occupants be exposed to extreme risk for a majority of the flight profile. The helicopter spends most of its flight time operating outside of the established safe autorotation envelope contained in the helicopter's height/velocity (H/V) curve. An autorotation is a descending maneuver, or power-off glide, which allows the helicopter to safely land in the event of a loss of power. The H/V curve is established by the helicopter manufacturer and is depicted by a graphical chart which illustrates which combinations of altitude and airspeed allow a safe autorotational landing in the event of engine failure. Operations outside the safe area of the chart expose the helicopter's occupants to extreme risk in the event of an engine failure. This is due to the fact that it is unlikely that the pilot will be able to accomplish a safe autorotation under this set of conditions following an engine failure, as demonstrated in this fatal accident. This area is commonly referred to as the “dead mans curve.” At the time of the engine failure, the helicopter was in a stationary hover out-of-ground-effect at 120 feet above the ground. This flight profile put the helicopter in the “dead man's curve.”

In light of this fact, an operator should understand these risks and elect to perform it's maintenance above and beyond the minimum recommended standards. The Company was very aware of these risks, yet they have demonstrated that the standard of care they used regarding their maintenance is well below that of the industry's acceptable standard of safety.

The Company had posted a video titled “Company is Seeking Pilots and Aerial Linemen.” In this video the President, states “You're taking two very dangerous things, electricity and hovering in the height velocity curve, dead mans curve, most of your career,” and, “Ninety percent of his (pilot) time is sitting in one spot (hovering).”

Federal Aviation Regulations (FAR) Compliance Requirements

An investigation of the helicopter maintenance records shows that the Company was using the airframe and engine manufacturer's maintenance programs. These maintenance programs allow the helicopter operator to maintain the airworthiness status of the helicopter on a continuing basis, provided the programs are strictly adhered to. The RR engine maintenance program was used to maintain the engine, however, the scope and detail contained in the scheduled inspections in the OMM chapter 72-00-00 Table 602 of that program was not strictly adhered to. This table contains the Inspection Checklist for each type of inspection, IE, 100 Hour Inspection, 200 Hour Inspection, etc.

As shown in Figure 1 above, the Company was either using an incorrect engine checklist or none at all for a majority of the 100 hour inspections. On only two inspections were the correct checklists used. The correct checklist required the fuel nozzle to be inspected each 100 hours whereas the incorrect and outdated checklist did not have this requirement. It was the use of this incorrect checklist that caused the maintenance personnel to overlook this critically important inspection item. The correct 100 hour checklist contained this fuel nozzle inspection, therefore, if the Company had been using the correct checklist, maintenance personnel would have realized that the fuel nozzle inspection was a part of the required inspection items.

According to the Federal Aviation Administration (FAA) such an oversight would be considered an issue of non-compliance with the manufacturer's maintenance program, and as such would constitute a violation of the FARs and breach the aviation industry's level of acceptance. This state of non-compliance would render the helicopter unairworthy due to the fact that the maintenance program was not being adhered to as specified by the scope and detail contained within that program.

The FAA has established the FARs to regulate and guide the operator to promote flight safety. Therefore, the FARs are material to flight safety. Non-compliance with the FARs materially affects the safety of flight since such a violation would have a negative impact on that which is relevant and significant to flight safety. Compliance with the FARs is the absolute minimum standard of care that an operator must abide by.

It is not clear at this time whether the Company was required to maintain the helicopter under FAR Part 91 or Part 135. This is due to the fact that this information has been requested but has not yet been produced. If the helicopter had been maintained under Part 91, the Company was in violation of Part 91 Subpart E, 91.409 (e). If the helicopter had been maintained under Part 135, the company was in violation of Part 91 Subpart E, 91.409 (c) (2) and Part 135 Subpart J, 135.421 (a) & (b).

Engine Overhauler (name withheld) Work Performed

Research of the engine maintenance records shows that the Engine Overhauler had performed an overhaul of the fuel nozzle, part number 23077068, and that the Company installed this fuel nozzle on the helicopter after the overhaul. Research of the Engine Overhauler's records of work performed on this fuel nozzle indicate that they did a functional test as received. The test indicated that voids and streaks were noted at all PSIs prior to any work being performed. They completed the overhaul per the Rolls-Royce Overhaul Manual 10W3, Edition 4 Revision 1, dated August 15, 2004, and complied with AD 2004-24-09, CEB A-1394 R1, incorporated MOD PMI G0005 and installed a new filter assembly, part number 139968, per Service Bulletin 1394. After completion of the overhaul, the fuel nozzle was tested in accordance with the Overhaul Manual to overhaul limits and the results were documented on the “Fuel Nozzle Calibration Record” form. This record indicates that the fuel nozzle had a final functional test performed after the overhaul to verify that it met all the overhaul limits as specified in the Overhaul Manual. The records show that the fuel nozzle met all the required parameters and did not exhibit any hysteresis or spray pattern anomalies.

The Engine Overhauler's procedures and records regarding the fuel nozzle overhaul are well documented, consistent with the regulations, and the standard of care exceeded the industry norm. There were no discrepancies, conflicts, irregularities or errors contained in those documents. Based on these observations, the Engine Overhauler performed the overhaul in compliance with both the FARs and the manufacturer's mandatory overhaul procedures and standards, and without any wrongdoing.

Conclusions

I have performed a thorough investigation and review of the documentation, and inspection of the accident helicopter engine components. As an expert in aircraft maintenance and operations, within a reasonable degree of certainty, my professional opinions are:

1. The overhaul of the fuel nozzle was performed in accordance with industry standards and was without negligence or wrong doing,
2. The fuel nozzle was functioning normally and and met all required specifications at the time of its release by the Engine Overhauler,
3. The fuel nozzle continued to function normally for hundreds of flight hours and months of operations after its release by the Engine Overhauler,
4. The work performed by the Engine Overhauler was in no way related to the malfunction of the fuel nozzle or to the failure of the engine, which occurred approximately 1097 hours after the performance of their work,
5. The Engine Overhauler did not breach any applicable standards, codes or regulations of any kind regarding its work performed on the helicopter's engine and components,
6. The Engine Overhauler's work performed on the helicopter's engine and components was not causal to the helicopter's engine failure,
7. The Company, as operator of the helicopter, had the duty to maintain that helicopter in accordance with the FARs and industry standards, but did not do so, failing to fulfill their duty as an operator and breaching an acceptable standard of care,
8. The Company did not maintain the helicopter's maintenance records in accordance with the FARs and industry standards,
9. The Company's substandard maintenance and record keeping, along with a disregard to follow the manufacturer's maintenance program, demonstrated a lack of standard of care and is inconsistent with aviation industry standards,
10. The Company substandard approach to maintenance led to the use of incorrect inspection checklists, which in turn led to the critical inspection of the fuel nozzle being overlooked,
11. The lack of proper fuel nozzle maintenance by The Company led to fuel nozzle streaking,
12. This streaking was allowed to go undetected due to the fact that the fuel nozzle was not being removed and inspected at each mandated 100 hour interval, thereby causing an over-temperature condition within the hot section. The over-temperature condition caused thermal stress and high cycle fatigue (HCF) of the 2^nd stage turbine wheel blade which led to the sudden engine stoppage. This inspection was critical since there is no other way to determine a localized over-temperature condition,
13. Items 7 through 12 above caused the engine failure which led to the fatal accident.

Lessons Learned

It is always a sad day when we have to look at a fatal aircraft accident to again be reminded of the obvious: Preventative maintenance is a very valuable tool and one that should be taken seriously. This accident should have never happened. It is my opinion that had the manufacturer's maintenance instructions been carried out, to the letter, this engine failure would never had happen.

Qualifications

I am qualified to review, analyze and offer my expert opinion regarding this accident based on the following experience:

I have 37 years of professional experience working in the aviation industry as both a pilot and as a mechanic. I have hands-on experience with the Rolls-Royce 250 series gas turbine engine, both from the operations side as a commercial helicopter pilot and from the maintenance side as a mechanic and Chief Inspector. These operations were conducted under FAR part 91, 133, 135, and 145 Repair Station. I hold an Airline Transport Pilot (ATP) pilot certificate, Airframe and Powerplant (A&P) and Inspection Authorization (IA) Mechanics certificates. This combined experience qualifies me to render expert opinion in this case.

Reference Documents and Data Reviewed

1. Rolls-Royce Engine Investigation Report, dated XX/XX/XXXX, including appendices A - J
2. NTSB Factual Report ID: XXXXXX
3. NTSB Probable Cause
4. NXXXX maintenance records including airframe and engine
5. Rolls-Royce 250-C20 Series Operation and Maintenance Manual (OMM)
6. Rolls-Royce 250-C20 Series Illustrated Parts Catalog (IPC)
7. The Engine Overhauler's records pertaining to work performed on engine CAE XXXXXX and components
8. Emails between Rolls Royce representatives
9. FAA issued ADs and RR issued CEBs applicable to this engine
10. Code of Federal regulations (CFR) Title 14
11. Photographs taken at the lab inspection
12. Photographs taken by Rolls-Royce expert
13. Letter dated XX/XX/XXXX from the Company to the NTSB
14. Rolls-Royce website at http://www.rolls-royce.com/
15. The Company's website at http://www.xxxxxxxx.com/
16. Complaint and Demand for Jury Trial, XXXX vs. XXXX, Cause No. CV XX-XX RFC

Can a Torqued Bolt Become Loose?

The answer to this question is, "Yes it can." But we need to qualify this answer. First lets eliminate the possibility of a nut rotating, thus loosening the torque. So now we are left with “how else can a torqued bolt become loose?”. OK here is one way that a bolt, after it has been properly torqued, can become loose. This phenomenon is call “embedment relaxation”.

Embedment relaxation is a phenomenon in mechanical engineering in which the surfaces between mechanical members of a loaded joint embed. It can lead to failure by fatigue and is of particular concern when considering the design of critical fastener joints such as in the through-bolts in the crankcase supporting the engine main bearings.

In critical fastener joints, embedment can mean loss of preload or clamping force. Flattening of a surface allows the strain (or preload) of a bolt to relax, which in turn correlates with a loss in tension and thus preload. Therefore, embedment can lead directly to loosening of a fastener joint and subsequent failure.
In bolted joints, most of the embedment occurs during torquing. Only embedment that occurs after installation can cause a loss of preload, and values of up to 0.0005 inches can be seen at each surface mate, as reported by SAE.

As each surface is pressed together, the high spots are crushed and deformed to form a surface capable of supporting the load.

Surface Finish:
There are multiple surfaces in the joint:

1. between the head of the bolt and the washer,
2. between the bolt washer and faying surface (faying surface is the surface of the object being fastened together),
3. between the two faying surfaces,
4. between the faying surface and nut washer, and
5. between the nut washer and the nut face.

Each of these surfaces squeeze together. Any paint, sealants, nicks, or alignment errors are gradually crushed down to support the load. Bolt threads also embed. Threads are pulled in shear, slightly increasing the thread pitch. Nut threads are compressed and lose a little pitch. As embedment occurs, the surfaces press further together and reduce the bolt's clamping force (preload). Note that relaxation occurs without any off-rotation of the nut.

Under optimum joint conditions in a lab one can expect between 1 and 11 percent. Obviously then, in the field, more clamping force can be lost. Lockheed did a lab test, Report No. LR 25049 where they tested 1 inch by 12 UNJF thread size L-1101 engine pylon bolts. They used lab conditions, with hardened steel bushings. In a static joint with no load fluctuations, between 1 and 11% preload was lost. The greatest loss occurred in the first eight hours after installation.

I have also read that the SAE did a study on this subject and they determined that as much as 20% of the preload was lost due to embedment. Some aircraft engine overhaul shops recommend that all the critical bolts on the engine be re-torqued after the first 25 hours of operations. This is most likely when the embedment has settled into a position where the surfaces are supporting themselves.

This may explain why some aircraft engine manufactures recommend that a complete 100 hour inspection be performed after the first 25 hours of operations after an overhaul or new engine is installed.

Checking the Torque on Critcal Engine Through-Bolts. How Important is This?

When you investigate aircraft accidents you get to learn some really important lessons. Usually by then it is a bit late. I was involved, as an expert witness, in a legal case where a TCM IO-520 engine had a catastrophic engine failure in flight. The crankshaft fractured and broke near the rear section and the engine instantly stopped producing power, which is what you would expect. Luckily no one was seriously injured.

The post accident investigation of the engine components revealed that the cause of the crankshaft failure was due to oil starvation to the main bearing journal. The oil starvation was caused by the main bearing shell rotating about 30 degrees within the main bearing crankcase saddle. The mating surfaces (parting surfaces) of the left and right crankcase saddles had signs of severe fretting. There were no other signs of fretting anywhere else in the case mating surfaces. Our determination as to the originating cause of the failure was that the through-bolts had inadequate torque. It had been about one year since the engine was overhauled and 440 hours. This was being maintained under Part 135 and was receiving 100 hour inspection. The records showed that no one had ever checked the torque of these bolts during their routine maintenance.

In this engine there are 5 main bearing saddles and each one has two through-bolts, one above and one below the main bearing saddle. This allows for a total of 10 through-bolts. These through-bolts are extremely important in clamping the entire case halves together and supporting the crankshaft. It was our determination that the clamping force was inadequate which allowed the bearing shell to rotate due to its loss of crush. It is this crush that keeps the bearing shell in place, not those two small tangs. This clamping force on each of the 5 main bearing saddles is supplied by the two through-bolts at each saddle.

The torque of these through-bolts is what sets the pre-load or stretch, which in turn applies the clamping force. It is this clamping force that resists movement between the two case halves. Even the smallest amount of movement between these surfaces will cause fretting. Fretting is a type of wear that occurs when two or more surfaces are in contact with each other under a load. Now if there is any movement between these surfaces, even at the microscopic level, fretting will happen. This fretting is wear, so now the surfaces are losing material which means that the clamping force will weaken as more material is lost, which in turn allows for more movement. Now you have a self-sustaining cycle which will progress rapidly.

The FAR's under Part 43 Appendix D contains a checklist of required items that is to be inspected for each 100 hour/Annual inspection. Below is a quote from Appendix D

(d) Each person performing an annual or 100-hour inspection shall inspect (where

applicable) components of the engine and nacelle group as follows:

(1) Engine section—for visual evidence of excessive oil, fuel, or hydraulic leaks,

and sources of such leaks.

(2) Studs and nuts—for improper torquing and obvious defects.

As you can see in (d) (2) it calls out for inspecting nuts for improper torque as part of the engine inspection. This is pretty vague as it does not specify exactly which studs and nuts to check. It is up to the mechanic to decide which ones they are going to check as it is impractical to check every one. Personally I would be looking at those that are critical verses non-critical. These through-bolts are the few that I would classify as “critical”.

So now you are asking, “if a nut is torqued why would I ever need to recheck it?” Well that is a good question and it deserves to be addressed in another topic so you will have to read my blog post on that subject here. Go here for that explanation.

The bottom line to this blog is that if the operator of this aircraft had spent the time to check the torque on these through-bolts, and had re-torqued them as required, then this failure might have been prevented.

When Is a Flight Manual Current?

I recently was asked if the Regulations required the operator to comply with a newly revised Aircraft Flight Manual Supplement that affected his aircraft. The issue here was that the original Supplement that accompanied a STC that altered the aircraft allowed for a GTOW of 3,800 pounds and was without any restrictions. The new Supplement which was issued at a later date now imposed a landing weight restriction, which would have an adverse affect on his operations.

This is very similar to my blog about the maintenance requirements, but is on the operations side. That is titled Turbine Operators Get Some Relief on Their Maintenance Program. I suggest reading this as it will give a better understanding of FAA's reasoning.

The FAA issued a Memorandum dated December 5, 2008 to clarify their definition of the word current as used in different areas of the Regulations. This specifically addressed the issue of maintenance but also describes how this is relative to the operations side. The exact same reasoning is applied to the operations of an aircraft wherein one must comply with the operation limitations as set forth in the approved Flight Manual. Again they address that a current Flight Manual is one that was issued at the time of delivery of the aircraft, not one that is current “as of today”. Following this logic would dictate that a Supplement issued to a Flight Manual is also under the same rules.

A summary conclusion is that if an aircraft were altered in accordance with a FAA approved STC and said STC had incorporated a Flight Manual Supplement which imposed certain flight limitations, then the operator of the aircraft would be bound by that Supplement that was current at the time of delivery. If then, at some later date, the STC holder decides to revise the Supplement, the operator may elect to incorporate that new revision into his limitations or may elect to ignore it. Remember the real point here is all about who can and cannot implement law and policy. The manufacturer can make recommendations, but only the FAA can impose legally binding requirements.

Parts Produced by an Owner or Operator. Are They Legal?

The answer to this question is yes, so long as that part meets certain criteria.

This is a subject that has a very profound affect on maintaining and modifying aircraft, and yet is widely unknown or misunderstood. It offers an alternative solution to the owner/operator, whereas it allows a person to produce a part to be installed on a type certified aircraft. Such a person need not be an FAA approved manufacturer. Of course this does not mean that a person may produce a part for an aircraft without following any requirements. It does mean that a person may produce a part, and that part will be eligible (read legal) to be installed on an aircraft, if he follows the FAA requirements for the production of that part.

Here is an exert from Federal Aviation Regulations

PART 21—CERTIFICATION PROCEDURES FOR PRODUCTS AND PARTS

Subpart K – Approval of Materials, Parts, Processes, and Appliances

21.303 Replacement and modification parts.

a) Except as provided in paragraph (b) of this section, no person may produce a modification or replacement part for sale for installation on a type certificated product unless it is produced pursuant to a Parts Manufacturer Approval issued under this subpart.

(b) This section does not apply to the following:

1. Parts produced under a type or production certificate.

2. Parts produced by an owner or operator for maintaining or altering his own product.

3. Parts produced under an FAA Technical Standard Order.

4. Standard parts (such as bolts and nuts) conforming to established industry or U.S. specifications.

This is stated in FAR 21.303 (b) (2) above but does not explain how this can be accomplished, only that it can. The intent of this is to allow owners a way to keep their aircraft airworthy if parts are unavailable or otherwise unobtainable. This does not mean that your needs must meet any specific requirements, such as the part is no longer produced or it takes six months to get it, but only that you follow the requirements of producing that part.

As this has been a subject that many have asked “how do I do this?”, the Assistant Chief Counsel for Regulations, AGC-200 of the FAA has written a Memo addressing this issue. I will summarize the main points of concern here.

1. Only the owner/operator can produce the part for their aircraft. They cannot produce that part for sale or for another aircraft.

2. The owner/operator doesn't need to actually produce the part but must be the “producer” by overseeing and directing the production process. This means that he may hire another person to make the part so long as he is directly responsible for the process by participating in the design, manufacturing and quality control.

3. The part must be produced using the same design data, material, process, etc. that was used to produce the original part. This can be done by using the original FAA approved design data or by reverse engineering the part.

4. The part is an FAA approved part as it meets the requirements of FAR 21.303

5. The producer must properly document the production process. All approved parts require this documentation process.

6. The part can be manufactured by either a certificated or non-certificated entity

Once the part is produced it will require the installation by a certificated mechanic or facility.

Turbine Operators Get Some Relief on Their Current Maintenance Program

The FAA released their legal interpretation of the word “current” as used in 14 CFR 91.409(f)(3). Here is the excerpt from that regulation:

(f) Selection of inspection program under paragraph (e) of this section. The registered owner or operator of each airplane or turbine-powered rotorcraft described in paragraph (e) of this section must select, identify in the aircraft maintenance records, and use one of the following programs for the inspection of the aircraft:

(3) A current inspection program recommended by the manufacturer.

This three page memo gets somewhat detailed and you can get a copy of it here:

http://www.faa.gov/about/office_org/headquarters_offices/agc/pol_adjudication/agc200/interpretations/data/interps/2008/Aircraft%20Maintenance.pdf

Basically the gist of it clarifies what a current inspection program really means. As an operator of a turbine aircraft meeting the above description you are required to maintain your aircraft in accordance with the inspection program recommended by the manufacturer. Now here is where it gets sticky.

If your aircraft is older, which the majority are, then the manufacturer has probably issued many revisions and amendments to the original inspection program. Most people were under the misconception that “current” meant keeping their program up-to-date with all those changes issued by the manufacturer, and therefore maintaining their aircraft in accordance with such changes.

This Legal Interpretation states that the “operator is not so obliged”. The real meaning of the word “current” in this regulation is “current at the time of delivery of the aircraft”. They also state that only the FAA can mandate rules that are binding on an operator and that such a mandate would be adopted in the form of either an AD or an amendment to the operating rules.

What effect can this have on an operator? Here is a real world example regarding Aerospatiale Alouette and Lama helicopters. These helicopters date back to as far as the late 1950’s. The original manufacturers’ inspection program did not contain any calendar inspection requirements for components. In other words, specific components had an assigned Time Between Overhaul (TBO) and/or a Life Limit for retirement. Somewhere along the long life span of these helicopters Aerospatiale, now Eurocopter, decided to revise the inspection program in the maintenance manual and added a 10 year calendar requirement for the inspection of components. According to the FAA’s own Legal Interpretation contained within the above memo, operators of these turbine helicopters are not so obligated to comply with any maintenance procedures that were not contained in the original current inspection program at the time of delivery.