I came across an interesting article in ITEM this past week about a Canadian helicopter that apparently has EMI problems. Like most such articles that I come across, I dutifully posted it in a variety of EMC related groups on LinkedIn. I do that for a couple of reasons. First, I believe its always a good idea to circulate relevant information to the EMC community. How can we not benefit as a community by sharing information of EMI problems, their causes, and (hopefully) their solutions. The second reason is that I greatly enjoy reading the comments of bona fide experts in the field. I think I learn more from some of the back and forth from them than I ever did actually working in the EMC field!
We certainly don’t get all the technical information from the article that we’d like as EMC engineers, but it appears that the big question is: was the aircraft EME properly considered in the development of the EMI requirements? As properly pointed out in comments on the article, it makes all the difference in the world as to who’s responsible for fixing this EMI problem. If the system was underspecified, that is, the EMI requirements were insufficient to preclude interference problems in the operational EM environment, and the contractor met those requirements, then the contractor has fulfilled his obligation and the customer would be on the hook to fund fixes for the EMI problems. If the system was properly specified but failed the required tests, then the contractor would be required to fix the problems (most likely, depending on the specifics of the contract). And someone else rightly pointed out that its ALWAYS cheaper to find and fix problems in the design stage than after a system is in production or even fielded and in use.
So which is it? Well, we may never know all the details we’d like to, but the article says that the Canadian government refused to accept the aircraft as being non-compliant. That would lead us to believe that systems failed specified tests. I agree with comments that I read regarding Sikorsky’s experience with military aircraft and EMI requirements, going back to the US Army Blackhawk issues. It would surprise me that Sikorsky would 1) be unaware of what would be “good” military EMI requirements based on a military EM operating environment and 2) try to somehow pass non-compliant systems off for acceptance. I hope we’ll get the full story details in the not too distant future. And all you EMC experts out there (you know who you are), please keep commenting because I’m going to keep posting. You’ll make a decent EMC engineer out of me yet!
– Brian Farmer