As aircraft become even more complex, the need for precise and accurate maintenance instructions increases. Back in the early days of aviation, a good mechanic could tell what was wrong with an aircraft engine by putting a long-handled screwdriver up to the cylinder and listening. Today, even the most-advanced diagnostic tools sometimes fall short. Having correct maintenance and troubleshooting guidance is essential for maintaining a safe aircraft and keeping it operational.

Most technicians have a good aptitude for learning aircraft systems, and training is a huge help toward understanding a system's intricacies, but no one can be expected to maintain an aircraft from memory. Even if that were possible, FAR Part 43, paragraph 43.13, Performance Rules (general) states:

(a) Each person performing maintenance, alteration or preventive maintenance on an aircraft, engine, propeller or appliance shall use the methods, techniques and practices prescribed in the current manufacturer's maintenance manual or Instructions for Continued Airworthiness prepared by its manufacturer, or other methods, techniques and practices acceptable to the administrator. . . .

The problem comes when these instructions are incorrect. Even though the manufacturer is required by regulation (Appendix H to Part 25, and Appendix A to Part 33 [engines] and 29 [rotorcraft]) to provide them, erroneous information can find its way into print. But since we as technicians are both bound by regulation and an ethical code to prevent an unsafe aircraft from returning to service, what are we to do when following the manufacturer's instructions would create such a condition?

Even more serious is when a maintenance instruction is ambiguous or missing. On Jan. 8, 2003, a Beech 1900D with two pilots and 19 passengers aboard departed Charlotte-Douglas, N.C., International Airport heading to Greenville-Spartanburg International in neighboring South Carolina. Immediately after lifting off, the nose of the aircraft continued to rise. The pilots struggled to get the nose down, but the aircraft began to roll and then struck a maintenance hangar past the departure side of the runway. All aboard died in the crash.

Accident investigators discovered that the day before the crash, technicians conducting a maintenance check found low tension on the elevator cables. Finding no specific instruction for simply adjusting the cable tension, the technicians adapted an existing procedure for rigging, but inadvertently omitted steps and ended up restricting the elevator travel. The aircraft was also loaded improperly in an aft c.g. position, and the two combined missteps were cited as contributing causes to the accident.

Maintenance manuals need to be correct and written with enough clarity of detail to ensure the task will be completed safely. Unfortunately, instructional errors are an all-too-common occurrence and become even more problematic to the maintainer when the system is complicated. To help maintenance managers and senior technicians address this issue, we looked into ways to handle the problem.

The Ticking Clock

The typical scenario for discovering a maintenance publication error involves a technician working on a task for the first time, and usually at night in advance of an important flight scheduled for the next day. Some of the most frustrating errors come in the form of an unexpected or contrary result during a step sequence. For example, the instruction could say to turn a thing clockwise to increase, when the correct direction is the opposite. While this is annoying, if you end up in the expected range, you are probably OK. But that raises the question: If directed action is incorrect, can the result be OK? Step sequencing is very important, especially when it comes to rigging and adjustment of sensors and switches. A wrong instruction will often result in pushing the system further away from the normal range, causing the technician to start over and adding significant time to the job.

Absent steps or incorrect value information can have much more serious consequences. Say you need to engage an interlock to prevent the gear from collapsing, or prevent an actuator from working while powering a system, but the manual doesn't contain this information. Even basic safety steps like fully deflating a tire and removing the core before taking the wheel assembly apart can have deadly results. Incorrect torque instructions can lead to either fracturing a fastener or leaving it too loose. In many ways, training and experience help technicians detect these types of errors and good practices can mitigate the dangers, but a good maintenance manual will have these steps included and with correct values.

The first thing to do after discovering a maintenance manual error is check the manual for currency and make sure all updates are present. Most OEMs have a method for checking both a paper and online pub's status, and that includes both permanent and temporary revisions. Remember, it is the technician's and manager's responsibility to ensure the pubs are current before starting a job, so it's good practice to double check the pub's status. If, after checking, you determine that the error has gone uncorrected, you should contact either the OEM's technical support office or local technical representative. You may not be the first one to discover the error, and a fix may be in the works. This is often the case on new model aircraft, but it happens to older aircraft as well.

If the publication error is minor and the tech support people have enough documentation readily available, they may be able to provide an immediate resolution to the problem. They can send an email or other official correspondence issuing an instruction, or clarification. You should keep a copy of this with the aircraft maintenance records. While this works well for Part 91 operators, those who operate under Part 135 or 119 may need to ensure that they can accept this type of instruction without updating their ops manuals. In addition, you should ask the OEM to commit to correcting the publication to avoid a repeat of the same problem.

When the manual errors are major, addressing the problem is much more involved. Technical data must be researched and reviewed by a Designated Engineering Representative (DER) or Organizational Delegation Authorization (ODA) Unit Member. This can take time — days, weeks or longer. Most maintenance manual data are considered “Acceptable” in the eyes of the FAA unless it involves an Instruction for Continued Airworthiness (ICA), which must be approved data and that approval process can take a while to complete.

According to John Bucher, an aviation maintenance consultant based in Castlewood, S.D., “Publication errors are really two issues — to get the correct information from the OEM to solve your problem or opportunity, and to get the maintenance manual corrected for the next person.” Bucher should know; before starting his consultancy, he spent 26 years as chief of maintenance at Honeywell's corporate flight operations. When confronted with bad information, he advises, “Call the OEM's service center and ask how they are doing it and returning the aircraft to service. Talk to friends in the industry for current advice. Work with the OEM's technical services to get engineering involved, and for manual revisions. Ask the OEM to communicate to you when the revision goes into the maintenance manual.”

One way to help spread the word of maintenance publication errors is to disseminate them on line via the NBAA's Airmail and through the NBAA Technical Committee, whose primary focus is to prevent problems by creating a conduit of information between NBAA members and the manufacturers. And the committee can use its influence to accelerate a response. “I have seen publication errors that have taken years to be resolved, and that is just inexcusable,” said Kevin Smith, chief of aircraft maintenance for Raleigh, N.C.-based Progress Energy Service Co. and a member of the NBAA Maintenance Committee. “The NBAA Tech Committee really has the ear of the OEMs and is a great resource,” he added. Visit the NBAA website:

Ethics and Pub Errors

Maintenance publication errors not only affect safety, but can raise ethical issues as well. Say you are going through a pre-purchase evaluation and you discover maintenance log entries for a task with known publication errors. Was the task performed correctly? Was it performed at all? We trust others in the community to do the right thing, and discovering a suspect maintenance entry can be disturbing if not illegal. Part 43.12 states:

Maintenance records: Falsification, reproduction or alteration. (a) No person may make or cause to be made:(1) Any fraudulent or intentionally false entry in any record or report that is required to be made, kept or used to show compliance with any requirement under this part. . . .

If you sign off on the task that you know is incorrect, are you violating Part 43.12? You are now stuck between a rock and a hard place. With no relief from the OEM, do you keep your aircraft grounded while you wait? It really depends on the type of error. If you cannot get the OEM to provide a response, you may have to take matters into your own hands.

“First off, is this a critical item? Or is it just a procedure that has been wrongly written and the operation of the airplane will not be impacted if the item fails to work as advertised?” asked John Gibson, president of Brush Prairie, Wash.-based Latitude 45 Aviation Consulting Services and an experienced business aviation maintenance manager. “If you can say, 'No, it's not flight critical, and yes, safety or operation will not be impacted if the system/part fails,' then you move to the next step. Talk to your folks. Brainstorm with them on what we all think the checkout should be, and reason your way through not only the system affected, but also any interactions with other systems on the airplane. Then, you make the decision, as the DOM, on whether, using your best judgment, you can release the airplane; you carry it out and you, as DOM, take full responsibility for the release.”

As cited in Part 43.13, you can use other techniques, provided you do not create a hazard. One source of information on “other” is Advisory Circular 43.13-1B, Acceptable Techniques and Practices — Aircraft Inspection and Repair. Although a bit dated, it still has good information on common maintenance procedures that you can use as the basis of developing your own repair.

Download a copy at:

When dealing with bad manual information, remember common sense combined with a good functional checkout or other verification of condition are always preferable to adhering to an incorrect publication. One word of caution: Do not presume a manual is in error for containing too many steps in completing a maintenance task and that the right thing to do is to create shortcuts. There may be a good reason for all those steps. Confer with the OEM and get concurrence before you implement a procedure that appears to be a time saver.

While to err is indeed human, as professionals we should demand responsiveness to correct a problem. If you are unsure of a maintenance instruction or statement, ask for clarification. Accurate and clear maintenance instructions are essential for safe maintenance, so do your part to ensure publication errors are corrected. BCA