AACs - Part 1-76 - Airworthiness Articles
Part 1 - Airworthiness Articles
Coaxial Cables - Environmental Effects
Rockwell Collins All Avionics Service Information Letters 1-91 and 2-92 have identified a possible source of system faults caused by the degradation of performance of RG-58 and RG-214 coaxial cables.
This AAC article is for INFORMATION ONLY and is issued to alert industry of the possibility of low temperatures affecting the performance of polyethylene dielectric coaxial cables, and possibly providing a solution to some unexplained intermittent system faults.
|Cold temperature environments may cause coaxial cables with polyethylene dielectric to back the pin out of coaxial connectors. The polyethylene shrinks more than the shield and outer insulation resulting in a poor if non existent connection at the coaxial cable/connector junction.|
|The problem is hidden within the connector and corrects itself in warmer temperatures . Arcing occurs at the contact point when this problem occurs. The arcing causes the destruction of the junction (high power) or a significant increase in connector loss when operating in cold temperatures.|
|High altitude contributes to the problem due to the decrease of the gap required for arcing. In many aircraft installations, the temperature may decrease lower than the expected -55 degrees Celsius.|
|Right angle coaxial connectors do not have the pin penetration, into the connector receptacle, that exists in the straight connectors and have a higher probability of this problem occurring.|
|For the reasons given above, Rockwell Collins do not recommend, unless absolutely necessary, the use of coaxial cables with polyethylene dielectric and right angle connectors.|
|RG-400 or equivalent can be used in lieu of RG-58 cable and RG-393 or equivalent can be used in lieu of RG-214 cable.|