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.