Menu Sign In Contact FAQ
Banner
Welcome to our forums

EMI/RF detection equipment in SEP

Dear all, as far as I have passed some AP and servo burnout issues it seems that EMI from one or more electrical aircraft sources could play a role in disturbing some sensors as well as some AP amplifier designs with the possible result of overvoltages or wrong gauge indications.
The reason why I think that EMI can play a role in some airframes is because i have little chirping and squeezing noises when switching the AP on, already on ground.
However according to the distance e.g. of the AP, servo and transponder cables or antenna I thought about doing some ground measurements as far as possible at all to high EMI emitting cables and sources. From my point of view the different options that airframes got from factory and any not re-checked avionic post mods can maybe have a certain effect on lifetime and durability of some sensitive electronic items.
However, would it be possible to localize EMI to certain “sense making extend” by a handheld EMI detector and to recheck the results after e.g. wrapping some cables with e.g. Amidon or any other metal jacking sleeves? Which instrument would you recommend to perform a more or less “rough” investigation?

TB20 Airman
Borkenberge EDLB, Germany

Also see Peter’s article about his KFC225 servos failing over France: https://www.peter2000.co.uk/aviation/kfc225/index.html – you want the part titled “September 2008 – with an amazing discovery!!”

tmo
EPKP - Kraków, Poland

Yes, I´ve noticed that article a while ago and doubted that EMI could have any significant effects to my ancient aircraft electronics from any outside RF source. Well, sometimes it appears to me that borders between esoteric impressions and physical phenomenons blur. Apart from my special technical interest in my request to the forum there are indeed some publications out there e.g. from polish researchers that are investigating and trying to detect biological risks of EMI (Michalowska et al. 2019 https://www.mdpi.com/1424-8220/19/24/5537/htm) link to the paper in GA.
If someone is looking up the internet one will find a lot anecdotes of possible EMI from aircraft systems http://www.rvs.uni-bielefeld.de/publications/Incidents/DOCS/Research/Rvs/Article/EMI.html but most of the reports correctly conclude that these observations are usually not reproducible. One hypothesis in the a.m. article I found was: “While entire aircraft are also subjected to some testing during certification, there may be individual differences between aircraft: if wiring connections are susceptible to interference, for example, then aircraft with a longer maintenance record may be more prone to interference incidents than brand-new ones.”

But these remarks lead away from my initial request how to find out if one could detect any unusual high radiation from certain internal sources that could be responsible for a relevant effect on avionics? and if – how to identify them or simply shield anything presumed on good luck?

TB20 Airman
Borkenberge EDLB, Germany

Yes; EMC is a very difficult issue. In production, one does an RF lab test (there is also a due diligence route in some countries) on a product and after that you just sell it and nobody asks any questions. For sure some some examples will be outside the spec, because so much depends on e.g. cable lengths.

In aviation, you get lots of issues e.g. the well known 11th and 13th harmonic of 121.xx etc VHF transmissions wiping out GPS, detailed here and elsewhere on EuroGA. In airliners, the build quality is a lot higher, especially when it comes to engine control systems, but the possibility of EMC issues is always impossible to completely rule out.

The KFC225 issue was never resolved officially. Yes, as noted above in that writeup, I had two or three servo burnouts above a particular point in France where there is some military installation, and this is very unlikely to be a coincidence. The KFC225 servo burnouts are highly airframe type dependent (90% in TBs, 100% in a Caravan, much less in PA46) plus one TB20GT owner who had a KRA10A RADALT reported failures every 20hrs or so! His (UK) avionics shop loved him; it was all done under the HBK extended warranty. Another one, Australia, ripped it all out and installed an STEC55X (cost ~50k).

One could rig up an antenna and a spectrum analyser and fly above that French site. Eventually with a lot of work you might get a fix but you could never implement it officially. Actually an unofficial fix for the burnouts is really obvious to anyone good in electronics but what you can never fix is the defective KC225 software which (almost certainly) destroys the servos with an aggressive periodic waveform.

There is specialised kit for recording RF, which you could fly with, but I have never used that.

Administrator
Shoreham EGKA, United Kingdom
4 Posts
Sign in to add your message

Back to Top