DME testing & accuracy standards
Asked by: Skyfox 5506 views Aircraft Systems, FAA Regulations, General Aviation
Is there any kind of regulation, FAA order, etc. that deals with the accuracy of DME? Going back to my King IFR course (on VHS!) and the book, they say that when checking the DME during a VOR check (for the purpose of IFR), the acceptable error is ½ mile or 3%, whichever is greater. AIM 1-1-7 b states, "Reliable signals may be received at distances up to 199 NM at line−of−sight altitude with an accuracy of better than 1/2 mile or 3 percent of the distance, whichever is greater," which I take to mean the overall DME system of transmitter + receiver, but it doesn't say anything about a requirement to test it or what to do in case it falls outside of spec. In my searching for information I came across AC 90-100A which in Appendix 1 part 4 b it lists what appear to certification standards for DME sensor accuracy which manufacturers must follow, which has changed over the years from ½ mile/3% down to .17 mile/.25%.
So, is there anything official that deals with this matter of checking a DME (particularly for IFR use) and which states what to do if the DME receiver in the airplane is showing a result outside that ½ mile/3% acceptable error from a known distance? Thanks!
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