Hi Group, I have a client that makes air conditioners for aircraft. They need to replace an obsolete fan (no longer available) with a newer version. Both versions have been tested for CE and RE and both pass the Category M limits by very good margins.
Here's where it gets interesting and where I need some advice. Apparently, they have been told by their local FAA engineer that while they meet the limits of DO-160G Cat M, they must demonstrate compliance by (a) installing their air conditioning system aboard (not sure how many) aircraft to ensure there's no interference issues OR (b) show the before and after emission plots to a DER (designated engineering representative) who witnesses the test and who recommends to the FAA to approve/disapprove. But get this...the "after" plot must be at or below the baseline "before" plot - at least in the critical frequency notches. The advantage of (b) is that the system does not need to be "flight tested" on X-number of aircraft. I don't believe any of the above (a) or (b) are written down in the standard...merely someone's opinion. The clients BIG ISSUE is that the original fan was a simple brush commutator motor, while the replacement contains an electronic controller. They've added a couple good-quality X2Y bypass capacitors to the power leads, as well as gasketing around the access cover, which knocks down the emissions by 20+ dB - well under the limit - but there are frequency bands where the emissions are a little higher than the baseline motor emissions. However, they are currently a good 10 to 25 dB under the limit. If their baseline motor was more complicated (i.e., had electronics), I'd suspect the A-B comparison would have been much easier. Here's a case where it pays to not have too good of a baseline! Now the questions... 1. Is the client's understanding of the qualification procedure correct? If not, then what? 2. I presume that the emission limits as specified in DO-160G have been calculated to reduce the risk of interference. Is it not sufficient to pass the limits or do they really need to jump through the additional qualification hoops described above? 3. Apparently the FAA engineer in (un-named city) has been proven to be more rigorous in interpreting the standard than other FAA offices. Is it fair to "shop around" for an FAA office with more reasonable interpretations? Thanks in advance, Ken _______________________ Kenneth Wyatt Wyatt Technical Services LLC Woodland Park, CO Email Me! | Web Site | Blog Subscribe to Newsletter Connect with me on LinkedIn - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
