By Pat Gray | March 1, 2009
Reflecting on the helicopter industry for the past 50 years or so, we’ve often seen events and developments that have taken place in spite of our lack of enthusiasm. Our industry is somewhat slow to notice what’s good for it but quick to isolate and eliminate the bad stuff. That’s certainly good, but why so slow to adapt to new methods and ideas? A case in point could be our present market in the medical field.
In the early and mid-1960s, the Helicopter Association International, HA of America then, in harmony with the U.S. Army, promoted the concept of medical evacuation for highway accident victims through a program called MAST (Military Assistance for Safety and Traffic). Designated Army Dust Off units were tasked to respond to civil requests for air transport of trauma victims and for hospital transfers. The history of medical evacuation was certainly there via the Korean and Vietnam Wars. Yet it took us well into the late 1970s before we even started to field civil helicopter ambulances. Yes, there were financial problems to overcome and equipment availability, but once the smart people figured it out, look at how it blossomed.
HUMS is on a similar path. It did not just suddenly appear yesterday. All of our major airlines have been locked into it for years and, as usual, the U.S. Army is leading the way for helicopter installations here in the USA. (Thank you Army, you have done much for our industry through the years.) We can talk cost and availability and so on, but we all know that in the final analysis, safety of our passenger and crews are paramount. We have the technology and product availability, now all you smart people, lets figure out a way to make HUMS universal in our industry.
Rotor & Wing received an invitation from Neill Osborne, president of ERA Helicopter, LLC to spend a day with his quality control (QC) staff in Lake Charles, La. to learn and share information about its health and usage monitoring systems (HUMS). On arriving at ERA headquarters in Lake Charles, it was immediately apparent that Neill and the staff were enthusiastic and proud of their achievements in the HUMS field. The director of QC, Jerrod Seabough, introduced me to Jason Alamond, the ERA HUMS manager who was to be my guide through the arduous task of HUMS explanation.
Jason is a former U.S. Marine, A&P licensed, steeped in dynamic component overhaul, and has worked for ERA for 11 years. He proved to be an excellent communicator and is thoroughly knowledgeable about all phases of HUMS installation and use.
In doing this story, I was struck by some memories of my early mechanical experiences while growing up. I came from the generation that learned how to tune up automobiles by changing and gapping distributor points and spark plugs, advancing and retarding the timing by turning the distributor and tweaking carburetor jets. All without benefit of electronic diagnostic devices. I distinctly remember one old gentleman who taught me how to take a long handled screwdriver and place the tip on the engine block and my ear on the handle to diagnose stuck valves, worn bearings, etc. An engine stethoscope, if you will. You never were certain if you guessed right about a problem until something actually broke and then you told your buddies, "I told you so". We never had enough money or time to do any preventive maintenance, but it was fun playing mechanic.
So, how far has the profession advanced since then? Light years if you ask me. Even though we are talking aviation rather than automotive, mechanical is mechanical. Read on to hear about some of the latest and greatest.
In the acronym HUMS. health refers to the vibration characteristics of the airframe and rotating components. Usage refers to flying/operating times. Some also include flight parameter exceedance monitoring, depending on the individual system capabilities. Vibration monitoring is used to identify the early stages of component degradation. Subtle changes in vibration signatures are recorded in flight, visualized on the HUMS ground station computer, and evaluated by a qualified technician. Alerts will signal the user of potential problems on board the aircraft to include monitoring rotor track and balance in the case for helicopters.
Visualize a spider web, if you will, spread over the working parts of a helicopter. At the center of the web is a black box called a signal processing unit or maybe a data acquisition unit, the brain of the HUMS system. The spider threads are actually a wiring harness with sensors at the ends that connect to critical helicopter parts. The electronic sensors are not very large, maybe a bit larger than the flat part of your thumb.
These little gizmos are quite sensitive, especially to vibrations, thus they often take on extra duty like picking up vibrations from adjacent equipment. For instance, if a sensor is placed at the out-put end of a drive shaft it will also pick up the vibrations from a hydraulic pump that is nearby. (More on this later.) There is definitely more than one type of sensor. A typical helicopter may have tachometers, accelerometers, velocimeters, even strain gauges. Temperature sensors are usually limited to cockpit gauges and warning lights.
The sensors pick up information like vibration frequencies, movement, RPM and bending moments and in electro speak, send the information to the data acquisition unit. This acquisition unit is busy recording all the events, (other sensors) segregating them, and preparing them to be read, at some point, by a technician.
At the start of the day the pilot or technician obtains a blank PCMCIA card and he inserts the card into a slot located in the HUMS control monitor located in the cockpit. The monitor automatically imbeds the type of helicopter and the tail number on the card and the system basically takes off from there. Some of the systems require the card to be programmed by the ground terminal. As the aircraft flies its mission for the day, the PCMCIA card is busy recording the information sent to it by the data acquisition unit. Prior to recording, systems will generally begin to perform built in tests. These begin at start up and are self-diagnostic. Depending on the HUMS system, when certain parameters are reached, say nr 85 percent, ng 50 percent, the systems are triggered to start recording.
After the last flight of the day, the card is removed, placed into a card reader at the technicians workstation and the information is downloaded to his CPU. I would add here that the pilot has very limited involvement in the HUMS system. He has a very small CDU (cockpit display unit) and he can verify that the proper PCMCIA card is installed and up-to-date. He also has an event button that can be used during flight. If he were to feel an unusual vibration and wanted to make sure it was recorded, he activates an event button that will recycle the HUMS to record all events and he can verify the new recording on his CDU. Other than that, it is a maintenance function all the way.
Jason explained the variety of systems installed on the ERA aircraft. In their inventory there are currently three different HUMS manufactures who’s systems are being used by ERA; a U.S. company, Honeywell, one from France M’Arms, and one from the United Kingdom, GE Aviation.
There are several factors to consider if you are wondering why one company would utilize so many different systems. The reasons are many and the decisions are complex. There are issues of system availability, support, approval for installation on a particular model, aircraft OEM involvement, individual system capability, fleet uniformity, customer preference and the list goes on. The bottom line is to improve overall safety while encompassing as many of these factors as possible. In the future, they hope to see more systems common to a variety of models. The development and approval process for these installations can be lengthy, but very beneficial in the long run. This uniformity would streamline training, spares, tooling and data management. Some HUMS manufactures are wisely positioning themselves to make kits for a variety of helicopters and they actively work with operators to obtain the necessary STCs as field add-ons. The drawing of the AW139 (below) shows the installation of the Honeywell system.
ERA operates a fleet of 140 helicopters worldwide. About 65 percent of this fleet operates in and around the Gulf of Mexico (they have 15 out-bases around the arc of the northern gulf) and this is where most of their HUMS installations are. The helicopters that have HUMS kits installed include three Sikorsky S76C++ and four EC135’s with the Honeywell VXP HUMS kits, 15 AW139’s with the GE Aviation HUMS kits and 2 EC225s with the French M’Arms kits.
First of all, it is an acronym jungle. Take recording units. One company calls it a signal processing unit (SPU) another calls the same unit a data acquisition unit (DAU), there are VELO, ICP and HTA’s, VXP, and so on. Most use PCMCIA cards for downloads but one uses cable that requires bringing a laptop to the aircraft. Does any of this create a significant problem? Not at all. The diversity is already there, and the methods used to manage the three existing systems are already in place. Although variances in terminology can be confusing to those who are not involved, most of the verbiage is relatively easy to correlate between the separate systems. To avoid confusion, concise descriptive communication is very important.
This is easily the most complicated part of using HUMS. At this point we know how the information reaches the field maintenance CPU. The technician who inserted the PCMCIA card into the reader at the end of flight operations is the first one to start analyzing the data. Fortunately, the software is very good, and it will convert the readings such as events and threshold exceedences into chart form.
His first scan is to see if any threshold exceedences have been recorded for that helicopter. If one is found, he has the authority to correct it, ground the aircraft if necessary, or take any other action that is appropriate. He also scans to see if other components are leaking out of their normal operating ranges. This requires more skill than a threshold alert. He must be aware of normal signatures and be able to spot minor deviances. In conjunction with the HUMS manager and other resources, it is then determined whether "close monitoring" or further action is in order. Most of the information downloaded is sent directly to ERA’s Information Technology Center located in Houston, Texas. Here, the different applications are run onto super servers and are made accessible to all authorized locations throughout the ERA network. With this setup, all discrepancies can be identified and analyzed by individual technicians as well as by the HUMS administrators.
How could moving, analyzing and storing all of this data possibly be efficient? Some of the data files can reach upwards of 30 megabytes of information. Fortunately, the file size varies from system to system. Some are small enough to simply e-mail, some will be on a server hosted by the HUMS provider, and some are managed by the Houston Data Center. So far, it has only created a minor bottleneck for ERA and with the advancements being made in the HUMS systems, it will be easier to mange in the near future.
Here is what the finished product looks like. See the chart above relating to a cooling fan shaft on an EC225. This chart gave an alert, directed the technician to the appropriate page of the maintenance manual, he removed some accumulated debris, did an inspection of the oil cooler fan shaft, did a non-flying check the next day, (some items require a flight check) recording the event and, as is obvious, the vibrations returned to their normal level.
It was mentioned earlier that most of the sensors monitor multiple components. In viewing a list for a AW139 helicopter with the GE HUMS system, the installation chart below shows a sensor designated A-10. It is installed near the number 1 engine input housing and is capable of recording an incredible eight separate events. The # 1 alternator, #1 hydraulic pump, #1 lube pump, left side second stage pinion, #1 AC generator bearing, collector, #1 alternate hydraulic pump and the TTO pinion. This particular HUMS system has 15 accelerometers and three tachometers attached to the helicopter with a total of 46 separate assignments. It takes a lot of experience, time and patience to learn how to differentiate between all the vibrations being picked up and to match them with the unit making the buzz. Each has a different frequency, but they have to be recognized and categorized. Overall, these sensors are very good and few problems or failures exist with them. Some connectors can be a problem, especially here on the Gulf Coast where salt spray and high humidity take their toll. As with other electrical connectors, corrosion can be a formidable adversary. Some electrical connectors are more vulnerable than others, depending on the material they are made of and the location aboard the helicopter. I would add here that the number of sensors is limited by the other components comprising the entire HUMS system and that weight is always a consideration.
Who sets base line standards and threshold limits? Actually, it comes from a combination of entities. Data from all operators of a particular system on a particular aircraft is sent to a central location as designated by the HUMS provider. This central location distributes the data among their engineers and analysts. At this point, data is screened and baseline fleet averages can be determined. A calculated percentage is added, and thresholds can be created or adjusted.
The aircraft or engine manufactures can also get involved to make their suggestions. The individual operators also report failures related to vibration levels so that the thresholds can be adjusted appropriately. This case specific data can be extremely valuable in setting effective thresholds. That can’t be bad. Most manufactures review thresholds every year and re-establish them based on fleet average operating experience. The fleets include very large helicopter operators both foreign and domestic and even the military, which are really big in the HUMS business. It’s a big circle with lots of information going round and round.
At the present time, ERA has been provided factory training on all systems that they have purchased. So far they have had factory training for 27 technicians with Honeywell VXP units, 21 on the GE Aviation systems and eight with the M’Arms systems. ERA also has ongoing OJT for technicians who are involved in the HUMS program. When factory training is available, ERA uses that opportunity to send the OJT personnel to the factory schools. A goal is to have this training done in-house. With the multiple systems and the variations in the systems, it easy to see that this would be beneficial.
When talking to Jason about this subject, he readily admits that support is adequate but hints that it could be better or more responsive. This is largely due to the various physical locations of the support teams. The difference in time zones sometimes presents a challenge for immediate response when services are requested.
On the way out the door after a long day at ERA, we had a few minutes to spend with Neill and get his input on ERA’s executive outlook toward the HUMS program.
The first thing he emphasized is that the program is a maintenance function and is a tool to be used for the overall well being and safety of the ERA fleet of helicopters. One of the biggest benefits is to reduce or eliminate the probability of catastrophic and premature failures of helicopter parts. He feels that the aircraft can remain in service for a longer period due to the reduction in vibrations. They have found that avionics last longer for that same reason.
Other benefits will be to increase operational readiness, easier maintenance scheduling, early detection to prevent secondary damage to internal parts and adjacent components.
The ERA goal is to equip the entire fleet with HUMS within a three to five year span. The cost will be high, but it is serious money for a serious program.