So I found another item of EMI interest to whine – I mean write – about: EMI in legacy equipment. You can find the article in question here.
In a nutshell, the FAA wants certain older cockpit displays (made by Honeywell) replaced because they believe them to be susceptible to interference from Wi-Fi systems that are going on board many aircraft today. It’s an interesting exercise for me to contrast my experience with the US DoD against the commercial flight/FAA world, and all I seem to have are questions:
1. Assuming that the equipment met the original EMI requirements, what has changed? Have the requirements changed? It certainly seems that the EM environment has changed. But this is a totally different paradigm than I’m used to with DoD procurements. The DoD specifies the technical requirements, including EMI, of systems that they purchase and once tested and accepted, the developer is done. If the device fails acceptance tests, including EMI, it’s incumbent on the developer to correct the deficiencies. How does that work in the commercial flight world? Are the requirements imposed by the FAA? Or by the airlines? Who certifies that the aircraft meets the specs and how? I’m sure there’s a process but I’m not familiar with it.
2. The potential issue was discovered two years ago in testing to certify the Wi-Fi system. So who gets the blame (i.e. gets to pay for the fix)? The source? Or the victim? This is a regular argument in DoD procurements when different program offices procure individual systems that are then integrated into a whole. Put a new radio on an aircraft, find out it doesn’t work because of EMI and who pays for the fix? The Radio PM (who may or may not have imposed and verified adequate requirements) or the aircraft PM (who presumable wants the latest and greatest capability on his plane and may have even been part of the specification process)?
3. And this is my favorite (thanks, Ken Javor!): If the original display units were qualified to DO-160D or later (as that model aircraft presumable was) level of 200 V/m, how could it be susceptible the Wi-Fi emissions, which would be more in the < 1 V/m range. There are additional interesting technical comments related to this question on the article in general in various EM related technical forums on LinkedIn; check them out.
Just so we’re clear, I certainly want the aircraft I fly on to be interference free and above all, safe! I’m not suggesting that the problem should not be corrected. Just that maybe there are options other than total replacement of systems. I bet some of the experts out there could find a fix that runs a bit less than total system replacement. But I’ve written many times in the past about correcting EMI problems after the fact, so don’t get me started! That’s not really the case here; it’s more about introducing a new transmitting system into the equation.
In the future, maybe everyone can connect to the in-flight Wi-Fi, log in to their favorite navigational app, and help the pilots fly to the correct destination….
-Brian Farmer
