By Richard Lippincott | Associate Fellow
The Lockheed Martin C-5 “Galaxy” transport airplane is one of the largest airplanes in the world, and is the largest in the U.S. Air Force inventory. Just shy of 248 feet long, it has an interior cargo deck 121 feet long, one foot more than the generally accepted distance for the Wright Brother’s first flight. The first of 81 C-5As rolled out in 1968, and after a dozen-year break in production, the first of 50 additional airplanes (designated C-5Bs) rolled out in 1985. Just over 50 of the airplanes remain in service today; they are all currently being upgraded with brand new avionics, engines, and instrumentation and are expected to continue flying for decades.
The mission of the airplane is to haul cargo (and to a lesser extent, people) globally as needed. This may be in support of U.S. or NATO military operations, but more often than not the airplanes fly routine logistical transport missions in support of the USAF and various government agencies. Two of the airplanes have been modified for special use transporting mission equipment for NASA. The C-5 fleet frequently flies humanitarian and disaster relief missions, whenever and wherever needed. Cargo loads are frequently in the range of 325,000 pounds or more, and the newest version of the airplane holds a world record for heavy flight with a gross weight over one million pounds.
None of this would be possible without a complete and thorough set of documentation used to operate, maintain, and repair the airplanes. An urban myth says that for airplanes like the C-5 or the commercial Boeing 747, the full set of printed manuals weighs more than the airplane. Not true, but for a C-5, the full set of printed documentation would fill 50 to 60 feet of shelf space.
Documentation subject matter starts with the flight manual (TO 1C-5A-1, commonly called the “Dash One”) and includes operation of all airplane systems, preventive maintenance, inspection, and repair. Inspections range from simple eyeballing to X-ray, ultrasonic, or magnetic particle methods of assuring the airframe remains within operation and safety limits. The documentation for exterior paint and markings alone runs to several hundred pages.
The content of the manuals is considered so critically important that they are designated Technical Orders, or TOs, meaning literally: the instructions within should be considered as orders, not suggestions, and must be carried out as written. With some new aircraft designs, the technical documentation delivery is considered important enough that the customer takes delivery of the manuscripts first (to begin training and familiarization), then 90 days later takes delivery of the airplane. In cases like that, a missed publication deadline can end up costing the airplane manufacturer millions of dollars.
In aviation, the consequences of documentation errors can be tragic. The May 1979 crash of American Airlines Flight 191 was traced to maintenance errors caused in part by problems in the service manual. The 2001 crash of American Airlines Flight 587 was traced, in part, to a deficiency in the flight manual.
Maintenance crewman Daniel Williams pointed out that sticking to the documented procedure is a protection in case problems come up later. He said that his instructors, “beat it into my head that the TO has a purpose, and that if something goes wrong and you were using the TO the answer given for the investigation should include the TO section, paragraph, and step with the statement while the aircraft is being repaired and the TO should also be changed.”
For decades, aircraft operation and maintenance manuals were distributed on paper. Updates were frequent enough that it drove a requirement for “change page” packages, partial publications of only the affected pages which would be inserted into the printed manuals. Printed updates were phased out starting near the end of the 20th century. Now the TOs are distributed electronically (typically as PDF), and updates come in the form of complete revisions. It’s faster, cheaper, and easier than the printed documentation. It’s also easier to ensure that a complete set of the TOs is kept with the airplane at all times.
The airplane maintenance manuals are organized on a three-tier system, often with separate documents for each level. From the simplest level to most complex, these are:
- Field/Organization—Tasks that can be completed with basic tools. Typical tasks at this level would be troubleshooting problems, and then removing and replacing a faulty component. Also included are replacement/replenishment of fluids or other system consumables. Simple mechanical or structural repairs are also permitted. Engines can be disassembled into major sections, for replacement.
- Intermediate—Rework and repair of faulty components, including recalibration of systems. Electronic systems can be repaired to the level of board replacement. Engine modules can be disassembled and repaired.
- Depot—Rework of electronics boards, major structural repair, major rework of structural systems, and machine rework/grinding of engine components.
Documentation in these categories ranges in detail and density based on the task at hand. Complex depot-level tasks may consist mainly of tolerances for grinding or other machine work, references to engineering drawings, or other forms where it is assumed the users have a high degree of skill and are mostly in need of specific data and measurements. Very simple and routine tasks may come in the form of a “job guide,” a pocket-sized document that spreads a procedure out over several pages, with simple steps on the left page and corresponding illustrations on the right. Another type of specialized documentation is the Time Compliance Technical Order, or TCTO. These are one-time use manuals that may mandate special inspections of the aircraft, or may come with a box of parts as part of a system upgrade.
Maintenance crews can perform field-level repairs while the airplane is away from the home base. Intermediate-level repairs are typically performed at the home base or another Air Force Base. Depot level work on the C-5 airframe is normally only done either at the Warner Robins Air Logistics Complex in Warner Robins, GA, or the Lockheed Martin facility in Marietta, GA.
Former C-5 maintainer Rich Jones recalls technical data helping during a mission. “We landed at Hickam AFB and the crew said they had a bogie pitch light.… We troubleshot the problem to a bad bogie pitch sensor and put it on order, which took 3 days for the part to come in. After removing and replacing the bad sensor, technical data said an alternate method for operational check did not require a jack and swinging of the gear. The flight crew and engineers balked at this at first, as they were clamoring for a jack. However, we had the TO to back us up and we showed them in the book in black and white that it did not require a jack to op’s check. We replaced the part and checked the bogie pitch sensor using the alternate method, I.A.W. technical data, and signed it off. Good to go. The good thing is, we had the technical data to back us up. Mission continued without problem.”
Quality assurance of the procedures is a critical requirement, stating that no procedure can be added to the Technical Orders unless it has undergone a complex process known as “validation/verification.” It is a two-level review, conducted first by the organization responsible for writing the documentation (in the case of the C-5, a tech writing QA team at Lockheed Martin) and then verified by repeat performance by USAF personnel. For more details on processes like this, see Emily Alfson’s article elsewhere in this issue.
After validation/verification, the documentation undergoes a thorough edit. The edit requirements cover more than just style, format, grammar, and spelling. Editors check to ensure that the documentation meets requirements for inclusion of safety admonitions, that illustrations are properly referenced, and also that all of the validation/verification comments have been incorporated.
Maintenance tasks on the airplane include those that are scheduled (lubricant replacement, adjustment of flight control components that come out of adjustment in the course of normal use, tire changes, system software upgrades) and unscheduled (repairs of components that fail). The scheduled tasks come at known intervals of either the calendar or airplane usage, the unscheduled are of course surprises caused by component failures. Troubleshooting to identify the cause of those failures
For unscheduled maintenance, the process usually starts either when the flight crew finds a problem (for example, the landing gear won’t retract, or worse, it won’t extend), or is notified of a problem by an onboard automatic diagnostic system with the awkward name “Malfunction Detection, Analysis, and Recording.” It is more commonly called MADAR (rhyming with “radar”). MADAR runs at the airplane’s flight engineer station, and provides a troubleshooting path to isolate the system failure. The system also provides fault codes that the crew can forward to the home base, this allows maintenance crews on the ground to start preparing for the repairs even before the airplane is on the ground. If this isn’t enough to pin down the problem to specifics, there is an additional set of fault isolation manuals that walk users through a decision tree, starting with symptoms of the problem and having multiple endings with solutions for each.
Once a problem is identified, the task is either performed or designated to be fixed at a higher level of maintenance. In either case, the work is done with the documentation nearby at all times.
Aircraft maintenance crewman Sean Sullivan put it this way: “TOs are there for a reason. Someone said you can’t remember everything and he’s exactly right.… These TOs are there for the safety of the aircraft, of course, but they are also there for the safety of all the personnel working on that aircraft.”
The Air Force encourages feedback to the writers, using an established process and forms. When crew members find errors, or simply know a better way to perform a procedure, they can submit a standard form (known as the “AFTO 22”) detailing the suggested changes. If approved, the form makes its way back to the technical writers maintaining the airplane manuals, and incorporated into an update. Technical communicators often never know if the documentation is being read or, if it is, how usable it is. The AFTO-22 process provides direct feedback from the users to the writers, and a peek into the mind of the user.
This is not to say the technical orders are perfect, no document is. Retired aircraft maintainer Tim Bowers recalls, “The R2 procedure for the system hydraulic pressure transducer is ‘Removal and replacement of the hydraulic system pressure transducer is obvious.’ Twenty five years later and I still laugh at that one.”
Technical communicators take pride in their work, but often are in a position of not knowing if the documentation is useful, if it meets the needs of the users, or for that matter if the users even read it. Writers on aerospace systems are fortunate in that they frequently hear first-hand about the use and the accuracy of the documentation. When disaster strikes anywhere in the world, it’s common to see those giant airplanes landing with food, water, medical supplies, and other materials desperately needed to help the survivors.
This is why we write: for the users, of course, but also for those whose desperate needs may be met only because an airplane is fully operational, reliable, and ready to go anywhere in the world when needed.
RICK LIPPINCOTT is an STC Associate Fellow, a newly elected member of the STC Nominating Committee, and former president of the New England Chapter. He has been writing about grand hardware (or, as he likes to call it, “heavy metal”) for over 30 years in such fields as aerospace, ion implantation, high-energy X-ray, and telecommunications.
