Avionics News July 2012 - 65

THEORY & PRACTICE
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LEGAL EASE

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is a failure waiting to happen – a latent failure. Wires and wire harnesses must never be installed under stress. Furthermore, all good quality connectors for aviation have some form of stress relief built in. The connector pins must never bear the weight and strain of the wire harness. The best form of harness support and strain relief is MS 21919 cable clamps installed in the proper manner as shown. These clamps will be padded so wires will not chafe.

avionics manual becomes part of the complete ICAs. In addition, if the CMM was developed to comply with an FAA requirement for ICAs (for example, to comply with ICA requirements associated with a supplemental type certificate), then the CMM is an ICA and will be subject to the FAA’s policies concerning ICA. However, if the CMM is not independently considered to be ICA, and if it is not referenced in ICA, then the CMM may not be ICA. If the CMM is not considered ICA, then it is not (currently) covered under the new FAA ICA policy. What is Not Covered? An important class of manuals not covered by the new policy guidance is the class of CMMs that are not considered to be ICAs. This is going to include certain avionics manuals that can be fairly described as non-ICA. This omission was not a mistake by the FAA. In developing the ICA guidance, the FAA recognized that non-ICA CMMs enjoy a different status within the regulations, and that they therefore were both more controversial and difficult to regulate. For these reasons, the FAA affirmatively chose not to include nonICA CMMs in the current policy guidance. This does not mean the FAA is ignoring non-ICA CMMs. To the contrary – the FAA recognizes these represent an important category of manuals that need to be regulated with careful and objective standards. The FAA affirmatively chose to address CMMs in a separate, later document, so that the regulator and the industry would have an opportunity to examine and comment on such a policy without mixing up the much easier issue of precluding anti-competitive behavior that undermines safety. Using the New FAA Guidance AEA Members who have not yet reviewed PS-AIR-21.50-01 should do so. Manufacturer members should assess whether the manuals they publish are considered to be ICA (some may not be ICA). For those that are ICA, they should assess whether their manual distribution policies are consistent with the FAA’s guidance. Repair station and operator members should assess whether the manuals they use are considered to be ICA. For those that are ICA, make sure to review any licensing agreements by which the repair station obtains the manuals. Such review should assess whether the licensing agreements are consistent with the new FAA policy. q
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MS 21919 clamps are commonly known as ADEL clamps. These clamps must be installed with appropriate AN or MS hardware, and in such a way so the weight of the cable does not exert a pull-apart force on the clamp assembly. I’ve looked under the panels of many aircraft without spotting a single ADEL clamp. I’ve looked at other aircraft and noticed ADEL clamps mounted improperly. If you see clamps mounted the wrong way, then a referral to your local avionics shop is in order. Still other aircraft have bundles supported with a large number of plastic wire ties. Wire ties have their place, but if you see 15 wire ties overlapping a messy-looking bundle, then you should be suspicious of the whole system. Some people try to cure the explosion in a spaghetti factory by zip tying the daylights out of the system. Wire harnesses must be installed away from, and above plumbing lines, especially fluid lines carrying flammable liquids. Most of these liquids will dissolve wire insulation, thus causing a short and spark. A fuel line leaking onto a wire harness mounted near an oxygen line is one way to turn a beautiful aircraft into a flaming lawn dart. The words above are a mere glimpse into the subject my instructor in college called, “installation considerations.” The best course of action is to get the assistance of an avionics professional before you make the purchase. Your local AEA shop can inspect the wiring and test the radios. Without test equipment, it is nearly impossible to determine the sensitivity or power output of a communication transceiver. The same is true with transponder and DME systems. The AEA shop can determine the modification status of your equipment and will have opinions about the overall reliability of the particular make and model installed. Buyers will always be glad they got two prepurchase inspections. q

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2012

Avionics News July 2012

Table of Contents for the Digital Edition of Avionics News July 2012