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"SAVE Me the Money"(ed. Jim Irwin's spin on the Jerry MacGuire rallying call) Most modern avionics are reliable and dependable in day to day operation. However, over time a lot of equipment may require the services of an avionics technician for repair or simply a tune up. For communication and navigation radios, a brief report of the symptoms to the technician is normally enough for him to know where to look when he gets the avionics on the bench. There, using specialized test equipment, he can usually confirm the problem reported in the symptoms report. This quickly allows the Tech to narrow the investigation to the items which potentially failed causing the problem. Occasionally, this type of investigation leads to a problem in the airframe such as a coaxial cable, connector, or antenna. Further investigations are required in these cases, but they all start with the report of symptoms from the owner/pilot. Autopilots are different since they interact with many other systems as well as the airframe itself. Each of these systems must be operating properly for the autopilot to do its job well. Since autopilot performance is directly affected by these other systems, problems can be more difficult to pin down. An owner/pilot can help the autopilot technician a great deal with a more extensive report and in doing so "SAVE Me the Money!" Frequently, seemingly unrelated events create problems causing poor autopilot performance. Examples could be maintenance in another area of the airframe or on another component. The installation of a new system or piece of equipment could change things causing autopilot performance to be affected. When you first notice degrading autopilot performance, stop and think about other activities on or around the aircraft that coincide with the development of the problem. You don't need to attempt to establish in your own mind what the relationship might be, just note the coincidence and make it part of your report to the autopilot tech. A few of the things we've noticed over the years that could influence your autopilot operation would be: a) Anything that is serviced, repaired or replaced in the aircraft control system. (i.e. an airframe paint job normally requires the removal and reinstallation of the control surfaces, a hinge replacement, a modification due to an A.D., etc.) b) Aging - the lubricant in the control system components can harden increasing friction. Increased friction could cause wing rock or pitch porpoise. Over time the control cables stretch along with the autopilot bridle cables (connecting the servos to the control cable) causing slack which degrades the autopilot responses resulting in wing rock and pitch oscillation also. c) The installation of new electronic devices, particularly RF/EM emitters, or high current equipment located near flux detectors or the altitude transducer can have an affect. Little things like an electronic engine tachometer with poor shielding on one of the magneto "P" leads can cause nearby equipment problems. d) Sometimes cable bundles from newly installed equipment are routed in such a way that they can affect the autopilot sensor cables routed nearby. e) Aircraft electrical problems, such as a low battery charge resulting from an alternator malfunction which could cause an AC ripple in the DC system can affect the autopilot, even though it is still charging the battery (i.e. a diode failure in the voltage regulator). f) An annual inspection - in the course of an annual the inspectors are all over the airplane and such activities could upset a weak coax connector, loosen something behind the panel, put a kink in a static line or change control cable tensions or a rigging adjustment, thereby directly affecting the autopilot performance. You get the idea I'm sure. When you are getting an autopilot performance problem attended to, in addition to describing the symptoms, think in terms of outside influences that may have caused an interaction with the autopilot. Some things reported to an autopilot tech which mean nothing to you and I, may be the thing that leads him straight to your problem and a quick rollout of your airplane - the quicker the problem is located, the lower the cost - "SAVE Me the money!" |