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HISTORY SPEAKS: NEW THEORY ON AN OLD AIRLINE CRASH?
Charles Odendhal III
Copyright January 2017
All Rights Reserved
Are HE Engine Failures on Jetliners Preventable?
Hydrogen Embrittlement (HE) became part of my life in the 1950s. I was one of several people employed at Shell (Oil) Development in Emeryville, CA, working to solve material failures in drilling equipment. Most failures were said to result from “Metal Fatigue”, but we knew they were most often caused by hydrogen embrittlement (HE).
A simplistic explanation of HE is that all metals are composed of crystals which can individually deform without damage if the amount of change is within their modulus of elasticity, even if large amounts of hydrogen atoms are present inside the molecules. Then, when stress is applied, usually by cyclic bending, the hydrogen atoms inside these molecules can migrate to areas where the crystals are being distorted beyond their modulus of elasticity. There the hydrogen atoms can collect between the crystals as hydrogen molecules and the hydrogen molecules and combine and separate the crystal grain boundaries; effectively reducing the strength of materials and often result in stress rupture and structural failure.
With no stress applied, the materials used in the drilling of oil wells will often pass all routine tests. However, when subjected to vibratory stress, HE would cause an otherwise sound part to fail. We tried to determine how to rid equipment of the hydrogen atoms, but we soon realized that measuring any excess of hydrogen atoms absorbed within materials during manufacturer was impossible. Still is today.
Uncontained failures in jet aircraft often result when parts of the engine, usually compressor blades, are cracked by HE and come apart inside the engine. Some parts will damage the engine, other parts, being uncontained, may shoot out at supersonic speeds and damage the aircraft, even damage other engines. Many uncontained engine failures can create sufficient airframe damage to result in total destruction and death. To date, there has been hundreds of uncontained turbojet engine failures and thousands of deaths.
Brief history of uncontained aircraft turbojet engine failures
During WWII, German turbojet powered aircraft suffered many uncontained engine failures and they either armored their engine’s housings when installed inside the airframe or mounted their engines below the wings so they could fall away in flight when the engines failed; not always safely. British military jet engine powered aircraft soon followed their lead; not always successfully.
The first turbojet powered commercial transport, the British Comet Jetliner, had engines installed inside the wings for more aerodynamic efficiency, because engines mounted outside the airframe used more fuel. However, Comet engineers also surround their engines with armor plating in a futile attempt to prevent airframe damage from uncontained failures.
The engines on most modern transport aircraft are located on wing mounted pylons or externally at the rear to prevent uncontained engine failures from causing damage to the aircraft. They are held in place by two “fused bolts,” which will separate under excessive vibration and allow an engine to fall away, safely, we hope, from the aircraft.
An engine installed internally was the cause of a dramatic United Airlines DC-10 crash on July 19, 1989, at the Sioux City, Iowa, airport. It suffered an uncontained failure of the center engine installed inside the tail section. The uncontained debris severed all the hydraulic lines, leading to a loss of flight controls. However, skillful use of the remaining two wing mounted engines saved many lives.
A recent example is the Southwest Airlines Boeing 737-700, with GE CFM-56 engines, flying between New Orleans and Orlando on August 27, 2016. It experienced an uncontained engine failure in the left engine during which the forward section of the engine nacelle was ripped off by a fan blade breaking loose and exiting the engine. A 5-inch by 16-inch hole was also found in the fuselage, just above the left wing. (Luckily the blade did not rupture a fuel tank and start a fire. Others have not been so fortunate.) The National Transportation Safety Board (NTSB) reported the cause was “Metal Fatigue.” It reads, “The fracture surface of the missing blade’s root showed curving crack lines consistent with fatigue crack growth.” These “Arrest Lines” are like tree rings showing periods crack growth or, in this case, periods of time under high stress.
Detection of crack growth in time to prevent failure
It may be possible to identify blade elongation during the period of initial material cracking, the first sign of failure. This can be done by detecting a significant reduction in the narrow air gap between a blade tip and the engine housing. This should prevent failures, rather than to inspect an engine at scheduled periods to try to locate defective blades, buckets or compressor and turbine disks during multi-hundred-hour inspections.
A more recent example is the American Airlines’ Boeing 767, with GE CF6 engines, that was taking off from O’Hare Airport, Chicago, IL, on October 28, 2016. Here, an uncontained turbine disk failure resulted in the destruction of the right engine. The disk exploded and the debris tore open a fuel tank in the right wing, resulting in a fire that melted the wing. One piece of the turbine disk was found over 3,300 feet away. While a Kevlar shield had been installed to try to prevent uncontained debris escaping from the forward fan section, the adjoining wing had little chance of escaping from being penetrated by debris from another engine section. Fortunately, the pilot was able to abort the aircraft take-off, bring the plane to a stop near the end of the runway, and everyone escaped relatively unharmed. Had the aircraft become airborne, all the occupants would have most likely died in an inevitable crash.
The November 14, 2016 article in the Chicago Tribune indicated that uncontained engine failures were not uncommon with GE CF6 engines; with over 4,000 similar engines in service to date. However, all makers, even Rolls Royce, have produced aircraft engines which have failed in a similar manner, many resulted in severe damage, some with total aircraft destruction and fatalities. This includes an engine on the Airbus 380, the world’s largest commercial transport.
Investigation of uncontained engine failures
During 1958-1960, I investigated uncontained jet engine failures with a metallurgical team based at Tinker AFB, Oklahoma City, OK. These failures and often fatal crashes of Air Force aircraft were largely assumed by engineers to be caused by metal fatigue, initiated by Foreign Object Damage (FOD). I was assigned to determine how much FOD depth on the leading edges of compressor section blades could be allowed to reduce the frequency of uncontained engine failures; since there appeared to be no way to eliminate them. (Still isn’t, 58 years later.)
It became obvious to me that most blade failures directly correlated with the duration of compressor stall or vibratory stress. This is where incoming airflow pressures varied in the engine inlet during take-offs and climb. A compressor stall would cause the blades most affected by airflow variation to vibrate the blades. Bombers seem to be most affected by such stress. Commercial aircraft also spend similar periods enduring compressor stalls, especially during take-off.
I secured relatively undamaged examples of blades from the overhaul area which were found to develop the most cracks in service and fitted them with strain gages. Then I mounted them in a base of dense metal and vibrated them in a high pressure airflow. When vibration frequency became a harmonic, the strain of the vibration would greatly increase and many blades cracked during tests, with no FOD present. In contrast, some blades with FOD would endure testing stress for longer periods without failure. Clearly, FOD was not as critical as the engineers would have us believe.
Engineers insisted that the greatest amount of strain was in the leading and trailing edges, with only moderate strain in the concave surface and very little on the convex surface. The areas where the engineers believed FOD nicks were considered to be the most critical was where my investigation was to be concentrated. However, I found many blades with cracks on their convex surfaces, located around 1/3 up from the base and 1/3 in from the leading edge, with no evidence of FOD. Due to my previous experience at Shell Development, I began to suspect HE as the cause and inflight detection of cracking as a cure.
GE engineers, responsible for the engines being tested, informed me that I was wasting time and money since they had already determined the most critical areas of stress, by theory. Besides, they claimed there was no way to test blades under service conditions, using strain gages, in an operational engine. However, I found a Chicago company which made a slip ring which could be attached to the nose of the engine and transmit the necessary strain gage information. I requested a stress testing program of blades in an operational engine, using an (unused) AFB base test cell.
I also found a material which would indicate the location and intensity of stresses during airflow testing. It was called Photostress Plastic and changed color in accord with the amount of strain. (Invented by Dr. Felix Zandmann of Tatnall Measuring Systems, Phoenixville, PA). Using this material and my vibration rig, this verified to me that the most critical area was located at 1/3 of span on the CONVEX surface. This also indicated to me that GE engineers had not fully tested blades for vibratory stress and the HE embrittlement I was trying to prevent.
Development of an impending engine failure device
I wrote a paper about my observations and detailed how a simple device could warn pilots of impending uncontained engine failures. I sent it to all concerned, including the Wright-Patterson AFB Research Laboratory, Dayton, OH, and GE Engineering, Evansdale, OH; manufacturer of the engines then being overhauled at Tinker; J33, J47, J57 and J79.
My invention, submitted as a suggestion, was a device which could be fitted to existing borescope holes, through which inside physical inspections are made in almost all engines. I believed that the outward movement of blade or bucket tips created by an initial material failure would be detected in-flight by blade tip contact with the device located in the engine housing and warn a pilot that a material failure was in progress. Two versions of my warning device were proposed. One would be a rub switch mounted in the borescope inspection port, which could warn of imminent failure. The other would have a proximity ability, which could measure the gap between blade or bucket tips and the engine inner housing wall, thus measure any change in clearance as a failure progressed. It might even be possible to measure the rate of elongation by this method, allowing for safe operation until the pilot could land safely.
There was no known interest shown on the part of the Air Force or GE engineers.
Then the secretary to our lab boss called me and asked if I would take the contents of the office waste paper basket to the department paper shredder. She was aware of my interest in anything related to blade failures and the hostility of our boss to my “meddling,” since he felt that I should be restricting my investigation to the simple testing of nick depth on blades to establish optimum FOD limits.
I was puzzled by her request (not being a janitor) until she indicated there might be something of interest to me inside the basket of waste paper. There I found a letter from R. I. Brown, Supervisor of Engineering at GE’s Evansdale facility. He clearly stated that “GE Engineering had never done vibratory stress level testing on the blades in question.”
I wrote a report for the Air Force in 1959 detailing the fact that FOD may not be the primary cause of uncontained engine failures. I explained that many uncontained engine failures may have been caused by incorrect manufacturing processes which allowed excessive hydrogen atoms to be retained within the metal of rotating components; which could be demonstrated to create cracks under vibratory stress, leading to material rupture and uncontained engine failures. I stated that the real cause of uncontained engine failures was most likely HE; an industry problem still with us today.I maintained that the then vacuuming of runways for FOD was probably unnecessary. I urged that more attention be paid to preventing failures by detecting the elongation of blades and buckets; many of which could be shown to rub the inside of housings long before failure. I also suggested a change in manufacturing procedures might reduce or eliminate HE. I also encouraged a change in aircraft operation to reduce compressor stalls.However, implying that the engine manufactures were the cause of engine failures was not well received and it was soon clear that my services were no longer needed. I resigned to do my own research.
Personal effort to develop my invention
I then earned a good living operating an auto repair garage, but never stopped trying to find a solution to uncontained aircraft engine failures.
To do this, I formed an Oklahoma stock company, the Oden Research Corporation, with my savings and money from investors, to research, design and test my concept in an operational engine. I also went to Dunlapp & Levy, Patent Attorneys, and paid them to do a Patent Search. They reported that the device was not patentable since the design had been patented in the past for a similar use with other rotating mechanical equipment.
While working for the Air Force, I noticed that blades scrapped for various reasons, including some with tips showing contact inside engine housings, were being sent to a commercial salvage yard in Purcell, OK. I later went to the salvage company and told them I was trying prevent uncontained engine failures. To my delight, the owner offered me an obsolete, but still operational J-47 engine for me to equip with subject blades and test with my proposed invention. He also allowed me to sort through the thousands of rejected blades obtained from the Tinker AFB overhaul facility; all free of charge.
I spent many hours sorting through hundreds of blades. I coated many with a special red dye which would soak into any cracks; which were not easy to see. I then cleaned off the dye with a solvent and re-coated the suspect blades with a white powder. The dye in any cracks would come to the surface and the red marks of a crack would become clearly visible, most of which were unrelated to any FOD.
Over a time, I acquired a fair number of blades that clearly showed cracks on the convex surface, with no FOD, just elongation. Some of the blades, when separated at the crack location, indicated evidence of cracking in stages, much like tree rings. This represented multiple take-offs and related stresses; suggesting the possibility of hours of flight time before failure. I also found blades which had rub marks on their tips, but which had come from engines that had not yet failed, indicating my device would have worked as designed. How long a rotating component would last after blade elongation was first detected in flight was the question, although the cracked blades found in the salvage yard suggested it might be many flying hours; allowing sufficient time for a safe landing.
With finances being tight, I was not able to move the engine to my rural property and install the defective blades for testing. However, I did design a reinforced structure to house the engine, which I hoped would contain any possible engine explosion; in the event I did get funding and my “Rotating Component Monitor” could be tested to warn of a potential uncontained engine failure.
Larry Booda, a reporter for Aviation Week and Space Technology Magazine, became interested in my project and arranged for me to seek federal funding for a possible method to detect impending engine failures in a formal meeting with the Senate Aviation Subcommittee on Aircraft Safety in Washington DC. I traveled from Oklahoma to attend the meeting. I must admit, I was in awe of the impressive room, with senators and staff, plus military brass from every service and several engine manufactures’ representatives in attendance.
I presented my proposed invention and illustrated its operation with examples of J-47 and J-57 compressor blades which clearly showed a slow progression in cracking before blade failure. This was counter by the GE engineers’ conclusion, again supported by USAF engineers from Wright Patterson Air Development Center, claiming that blade failures happened too quickly to be detected in any useful period of time. I considered this “No time to avoid failure” claim as an assumption, but it was repeated many times years by GE and USAF engineers. It seems that they simply didn’t want to spend the money to seek any possible method by which HE could be recognized, avoided or prevented; something which might save lives.
At the meeting, I was informed that the sub-committee would consider my proposal and my request for funding. However, while leaving the meeting, a young GE representative told me, “Your presentation made sense, but nothing may happen.” Then another man, with no identification, demanded to know where I got the blades used in my presentation. I told him, “They came from a Purcell, Oklahoma, salvage yard.” He said, “We’ll checked it out. If they are found to still be Air Force property, you could go to jail.” A more mature representative of an engine manufacturer called me over on the way out and said, “Son, to recognize your device, we may have to admit that we are producing engines that are prone to self-destruction and the Air Force may have to admit that it has been buying them for years knowing they are subject to unpredictable failures over which they have no control. We are working hard to produce a safe engine and every crash only makes us work harder.”
I asked, “Why have crashes, when crashes might be avoided by a warning system?” There was no response. This was repeated in a Norman, Oklahoma, newspaper article on my efforts, again with no response from anyone in the aviation industry.
End of my dream, wonder why not one else tried
Upon my return home, I learned that my request for funding had been denied and I was very discouraged. Then, the owner of Purcell Salvage asked me to meet him at Westheimer Field, where I based my airplane. He met me at dusk and asked that we walk over to my airplane; tied down on the flight line some distance away. He led me to the side of the plane away from buildings and told me to look towards the airfield runway so our conversation could not be observed. Then he told me, “You really pissed off someone (important?). It would be best you never come back to the yard.” He implied it might not be physically safe for me.
Therefore, without funding or access to an engine or blades for a demonstration, the Oden Research Corp was dissolved and my attempt to develop an aircraft engine warning system ceased. My car repair business was also unfairly shut down by the IRS.
I eventually found work as an engineer for a British Leyland car distributor, investigating Jaguar, Austin and MG car mechanical defects in the western USA.
However, it seems inconceivable to me that hundreds of people with far more experience and greater qualifications have kept silent. Surely, NTSB investigators and engine manufacturers’ engineers must have known of the dangers of HE and its role in uncontained engine failures AND the need for a warning of impending rotor blade and disk failures. After all, my warning about what was causing rotating component failures and how my device might work to prevent them was sent to the Wright-Patterson AFB Research Laboratory in 1959, with detailed explanations published in both local and national publications in 1965; 58 and 52 years respectively.
Yet there are still uncontained engine failures and there seems to be little mention of HE in accident investigation reports. One must wonder how far back HE was known to metallurgists and engineers as the primary factor in accidents caused by “Metal Fatigue,” so commonly blamed for accidents. I know that HE was a factor in USAF accidents at least 60 years ago, perhaps earlier, but everyone, except me, seems to have remained silent to this day.
There have been recent efforts to protect the public and pilots from uncontained engine failure, but wrapping Kevlar around the fan section of an engine has not been too successful.
What about the loss of engines, loss of aircraft and, more important, the loss of life? The loss of one engine might pay for the retrofit of hundreds of rubbing contacts. The loss of one aircraft might pay for a retrofit to an entire fleet of aircraft. The loss of life cannot be measured.
While my device may not work as designed, that has yet to be proven. Meanwhile, uncontained engine failures will continue to cause aircraft crashes worldwide, with the increased potential for an even greater loss of life in a single event.
Charles Odendhal III, 819 35th Ave., Greeley, CO 80634 970-371-0934 email@example.com
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