Friday, August 1, 2008
Keeping the Big Boys Flying
On any given day, the U.S. Air Force’s Air Mobility Command (AMC) completes more than 200 airlift missions carrying more than 1,000 tons of cargo and some 2,500 personnel, often flying into some of the most environmentally and/or militarily hostile areas of the world.
Most of that is accomplished using two of the world’s largest cargo aircraft, the C-5 Galaxy with a 135-ton payload capacity and the 80-ton payload capacity C-17 Globemaster III.
Simply keeping aircraft of that size flying is a task unto itself. Keeping them flying under the conditions imposed by operations into global conflict or humanitarian relief following natural disasters adds significant complexities.
"The biggest challenge is that the aircraft can be deployed off station for up to 60 days at a time," says Col. Tammy Livingood, Commander, 437th Maintenance Group at Charleston AFB, S.C. With some 50 C-17s based at Charleston, it is the largest C-17 base in the world, all under Col. Livingood’s maintenance care.
"The challenge is that the aircraft can accumulate discrepancies as it travels around the world doing its airlifts," she says. "As it stops to download cargo or people at the different locations, it has minimal enroute maintenance performed at those locations. In some cases, there is no maintenance being performed."
When an AMC aircraft leaves its home station, it becomes the responsibility of the Command and Control Directorate within the 618th Tanker Airlift Control Center (TACC) at Scott AFB, Ill., which tracks every flight in the world, from the time it takes off until it returns to its home base. This includes constant monitoring of the aircraft everywhere it lands and its position along its route of flight. When an AMC aircraft breaks down while on an AMC mission, the Logistics Readiness Division (XOCL) leverages the entire AMC logistics enterprise to expedite repair.
This means working hand-in-hand with the Flying Crew Chief (FCC) or en route maintenance team on the ground to diagnosis the problem and identify the parts, equipment, and maintenance specialists needed. Then XOCL matches resource locations with the quickest transportation to the broken aircraft in order to accelerate the repair action. For example, last month a C-5 was broken at Elmendorf with a fuel system problem. Travis AFB in California was the closest AMC unit, but Dover AFB in Delaware had the part, maintenance specialist and quickest transportation to Alaska. Less than 20 hours later the aircraft was fixed and back on the road. On average, aircraft that break while flying AMC missions are fixed in less than 39 hours, a repair velocity the Air Force says is absolutely critical to keeping the AMC Global Reach mission moving.
Flights of the C-5 and C-17 out of the continental United States, with the potential for maintenance problems in less-than-ideal locations, include an FCC. While an AMC aircraft is flying away from home station, they are the first, and most important, step to a timely and accurate diagnosis of the maintenance problem and a rapid off-station recovery.
"If the repair is within the FCC’s field of expertise based on his Advanced Systems Training, he would advise the XOCL that he can repair it, giving the XOCL an estimated time in commission, when the airplane will be fixed," says Tech. Sgt. Mark McClish, a C-5 crew chief and the FCC program manger for to the 436th Aircraft Maintenance Squadron (436th AMXS) at Dover AFB.
"He would then call back to his home station, advising them of the problem and requesting permission to fix it." McClish adds.
If the FCC does not feel comfortable fixing the aircraft, he advises the XOCL, which will then determine what additional equipment and/or personnel are needed and send a recovery team from the nearest capable base.
Disposition from damage to a major system, such as destruction of an engine, depends on the location, McClish says. "If it’s in a hostile area, the aircraft commander may receive permission to fly out on three engines to a safer and more capable base. The aircraft is very redundant, capable of flying on back-up systems. Most likely though, [XOCL] will bring out another C-5 to take over the original mission and haul out a new engine to replace the damaged one, along with all the necessary equipment and personnel needed to replace the engine."
Once an aircraft has been broken for 48 hours, "they are briefing their 4-star generals at AMC — what the status of the aircraft is, how they are getting it fixed and what support they need," Livingood says. "It’s a big system that reacts very quickly."
There are also situations where the maintenance required can be dealt with by the aircraft’s crew, but not exactly according to the book.
"A lot depends on whether it is a maintenance issue or an operations issue," McClish says. "The idea is often to get the aircraft out (of its current location) as quickly and safely as possible." This may be based on hostile activity in the area, or simply because the massive aircraft is taking up too much room on an airfield used by other foreign militaries or as a civilian airport.
While a systems issue may be "good to go" based on the maintenance manual, the operations book may say the system has to be on line, he says. "The two (manuals) do not always line up as to what’s required. So they have what is called ‘mission essential’ to determine what action to take in a ‘go, no go’ situation — what is essential for flight and what can be left out of a specific system or subsystem and still allow the aircraft to fly safely."
The aircraft crews always keep their home base maintenance commanders advised of what is going on, Livingood says. "If it is significant enough that they need permission from the home station to do something that is maybe not authorized, they would then call me saying they need a waiver to do what needs to be done. Typically, I can do that over the telephone," she continues. "They will then enter into the [on-board communication] computer that they called and that I gave them permission. They will also forward the information to the XOCL that I’ve given them permission to do that."
"There are constant communications with Boeing engineers, whether they are at Charleston or anywhere around the world, asking their opinion [on the maintenance problem] — what do they recommend, what are the risks, how far can the aircraft fly, at what altitudes, under what restrictions, that kind of thing," Livingood says.
She also notes that Boeing engineers are very much part of the C-17 program, based on the airfield next to the maintenance headquarters. "They are part of the production meetings every day. Boeing sends its engineers, its field reps and flight managers to the meetings to help us solve problems, or if they have an idea that we haven’t thought of, or they volunteer their people when needed."
"If there is [a C-17] that is disabled, somebody at Boeing will know it," according to Roger Law, Boeing’s site manager for the C-17 at Travis AFB. "Nothing happens without Boeing knowing about it because we are very intimately attached and involved in what our customer is doing."
While the system is well established to deal with maintenance emergencies in remote locations, most maintenance is "O Level," taking place at the aircraft’s home base within the United States, with work being done both inside a hangar and on the ramp.
"The major challenge for working on the C-5 is its sheer size and complexity, with the complexity going hand in hand with its size," says Senior Airman Ryan Hart, also a C-5 crew chief with the 436th AMXS at Dover AFB.
"For instance, the landing gear on the C-5 is like none you’ve ever seen, which is a product of the size and weight of the aircraft. So its size makes it a bear to work on," McClish adds.
The C-5 Galaxy is 40-year-old technology, developed in the late 1960s and becoming operational with the Air Force in June 1970. It is also the Air Force’s largest cargo airlifter, with a cargo bay longer than the Wright Brothers’ first flight and wide enough to hold an eight-lane bowling alley. It contains more than 100 miles of wiring, over five miles of control cables and four miles of tubing, and the weight of the fuel to fly it is about equal to the maximum gross weight of the C-141A, with sufficient fuel for the average American car to make 130 round trips between New York and Los Angeles, or 31 trips around the world.
The size of the aircraft also impacts the maintenance training required, McClish notes. "A lot of it is just learning the aircraft from someone who knows the aircraft already. As a hydraulics mechanic I can go to work on the hydraulics on any aircraft. There are smaller aircraft out there that when you’ve worked on them for 10 years, you know every nook and cranny. You just do the task and learn from repetition, doing it over and over. But I’ve been working on the C-5 for 10 ½ years and every day I learn something new. There are some tasks on that aircraft that I’ve never done. That is because some of the parts don’t fail as often as some of the other higher failure items," he points out.
In fact, there are some maintenance tasks that the Air Force doesn’t even provide instruction on, leaving that up to the manufacturers. Law noted that if the aircraft’s HUD system goes out of alignment, a Boeing team would be dispatched to perform the alignment. The Air Force doesn’t teach HUD realignment because it happens so rarely. "So that would take a unique [Boeing] team with unique and very specialized tooling to correct in the field," Law says. Boeing also provides a depot-level field team to help out when there is a maintenance requirement at the O Level but no procedure for the Air Force maintainers to do it, he says.
Because of its size, any maintenance personnel working on the C-5’s wing or fuselage must be tethered to the aircraft, using a "leap frog" method of attaching harness lines to attaching points as the mechanic moves along the top of the fuselage. This also means that wind plays a large part in performing maintenance on the exterior of the aircraft.
"We cannot be on any upper surface if winds are getting up to 25 kts," McClish says. "Jacking the aircraft up is also limited by the winds. If the wind is even forecast to be up to 25 kts, the aircraft cannot be jacked up. It’s a matter of not having enough time to get it back down if the winds do start to blow at that speed."
If the aircraft goes down for maintenance in remote areas where the winds are always high, "then we have to use Operational Risk Management to determine what has to be done versus what needs to be done," he adds. "We can’t go against the book, but we can get waivers if absolutely necessary."
Despite its size, the C-5 only requires two special pieces of equipment that are unique to the aircraft, according to the crew chiefs. The first is a 500 gallon nitrogen truck. Liquid nitrogen is used for fire suppression and fuel tank inerting, McClish says. The nitrogen replaces air in the fuel tank so that if there is an accident, there is no oxygen in the tank to cause a fire. Each C-5 carries 1,500 lbs of liquid nitrogen, or roughly 223 gallons.
The second requirement for the C-5 is a means of getting 65 ft into the air to work on the T-tail of the aircraft. For work on the ramp, a specially designed cherry picker that will hold two people is used. For work in the hangar, a 73-foot high "dock" can be rolled into place around the tail, then sliding floor panels moved up against the airframe.
Programmed depot level maintenance and modifications for the C-5 is done by Warner Robins Air Logistics Center at Robins AFB, Ga. Mission readiness goal for the C-5 fleet is set at 75 percent. That rate had been achieved in the early 1990s during Operation Desert Storm, but dropped to 68 percent in 1994, then to 58 percent in early 2001, according to globalsecurity.org. This was primarily from the shortage of spare parts. Reliability rate of the C-5 is now reportedly back up to around 70 percent. Maintenance manhours (MMH) per flight hour (FH) have also been dropping since reaching a high of 58.44 MMH per FH in 2005. They were down to 40.52 MMH per FH in fiscal year 2007 (FY07) and 32.83 in FY08. The C-5 does, however, have roughly twice as many MMH per FH as the C-17. In FY05 the C-17 reported a 23.97 MMH per FH, going down to 20.39 in FY07 and 15.73 in FY08.
Unlike the C-5, the C-17 does not have a standard program depot-level maintenance with the aircraft being sent to a specific maintenance depot, Livingood said. However, every C-17 does get a home station check every 120 days. "This is about a three-day check where we inspect different items on the aircraft," she says.
There is, however, depot level work on the C-17 to modify older aircraft under the USAF and Boeing reliability modification program. "So it’s not necessarily a depot check where you take the whole airplane apart and put it back together."
The special depot maintenance is done under a Time Compliance Technical Order (TCTO) normally to perform modifications on older aircraft to bring them in line with new aircraft coming off the Boeing line in Long Beach. This can be performed either by Air Force personnel or by Boeing, Law says. "It’s not necessarily that [the Air Force] can’t do it, it’s just that they may be busy launching and recovering aircraft, or maybe their folks are deployed and just not available. In those cases, the Air Force will turn the aircraft over to Boeing." The manufacturer maintains Recovery and Modification Services (RAMS) teams on site at the C-17 bases, so if it is asked to perform a depot-level TCTO, it will typically use a RAMS team, he says.
The only special Air Force equipment unique to the aircraft is the engine trailer that allows an engine to be carried out to the aircraft and lifted up for attachment to the pylon. Getting up to the T-tail is via a lighted stairway up through the tail to the horizontal stabilizer. There is also a "trolley" that allows a mechanic to lie on his back and scoot under the fuselage just as an automobile mechanic gets under the family car.
However, Law states that "sometimes a specific job can’t be done using current configuration and support equipment. One of the benefits of having on-site engineering is that they can come up with an alternative method to meet the same intent to accomplish that level of maintenance. And that is a significant benefit that Boeing Engineering and Support Group at each base provides. They have trained engineers who understand the aircraft, so they can actually modify or redesign certain tools or support equipment to help facilitate a maintenance activity that the depot team does."
Livingood notes that the C-17s at Charleston AFB have a mission capable rate of 85 percent, "which is quite high." The logistics departure rate of the aircraft is in the 95 – 96 percent range. "So when it is flying around the world performing its missions, it is able to take off around 95 to 96 percent of the time, which is an incredible number for the warfighter to be able to rely on the C-17," she says.
The key to the reliability of the C-17 is its redundancies and the advance technologies built into it, including a built-in computer that can diagnose and pinpoint problems.
The aircraft was originally designed by McDonnell Douglas based on that company’s experience with the DC-10 and MD-11. The first C-17 was delivered to the U.S. Air Force in June 1993 and declared operational in January 1995.
The C-17 Globemaster III is the jet "big brother" to the Douglas C-74 Globemaster I that was in service with the Air Force from 1945 to 1955, and the Douglas C-124 Globemaster II used by the USAF, Air Force Reserve and Air National Guard from 1950 to 1974.
Since its entry into service, the C-17 has been supported through Boeing’s Globemaster III Sustainment Partnership (GSP) program. This, in turn, is part of Boeing’s Total System Support Responsibility plan and the framework for meeting the company’s pre-established, definitive goals established for the program’s Performance-Based Logistics requirements. In March, Boeing was awarded a $273.3 million contract by the U.S. Air Force to continue providing maintenance on the C-17.
"This is not your father’s airlifter," Law says. Like most modern aircraft in the world’s commercial airline fleets, the C-17 is highly computerized to increase reliability and reduce maintenance man-hours. This includes an Aircraft Supportability and Integrity Information System software application that calculates maintenance requirements and inspection dates for installed parts, a Maintenance and Modification Plans and Scheduling software package, and iCapture, a PC-based software application to simplify the process of creating a nonconformance discrepancy at the point of discovery.
Additional software packages perform the maintenance tasks found in most major airline maintenance operations.
The support program also involves the supply realm, Law says. "We have a responsibility to deliver certain Boeing managed parts, to get them from point A to point B in a critical period of time."
Boeing also constantly upgrades the aircraft through its Global Regional Improvement Program (GRIP) at the Boeing facility in San Antonio.
"The C-17 is all new technology," Law says. "It was built with input from the loadmaster, the pilots and the maintainers. As a result, it has characteristics that have eliminated many of the maintenance intensive tasks that you would typically face on the C-5 aircraft. The C-5 is a great airplane, but it has a reputation of having a very high maintenance hour to flight hour ratio."