[digidocs]

I wonder which (if any) EFIS systems can withstand lightning induced electrical surges. As I contemplate an all electric IFR panel, a lightning hit "strikes" me as a single point of failure worth considering. I realize that lightning hits are relatively rare for aircraft of our class but I saw a thread here the other day on a single-engine experimental that took a hit while VFR a significant distance from a TS. Unfortunately, despite my best search efforts, I can't find it at the moment. Also, this article (1) claims that commercial birds get hit once every 1000 hrs or so.

There is actually quite a bit of information out there on what is required of certified avionics to resist lightning surges. To make a long story short, it looks like avionics tested to DO-160 waveforms 3 and 4 at voltage level 3, would stand a pretty good chance (2). This basically boils down to being able to withstand 600V for 5uS and 300V for 70uS.

Do any of the EFIS manufacturers design for or do any DO-160-like lightning transient tests? If the Microsemi TVS app note (2) below is accurate, it looks to be relatively straight forward to add such surge resistance to an existing design. I'd love to know if any existing products have this protection, it sure would add a bit of peace of mind.

Sorry for the technical post, but I am an EE and I think this is an important consideration with an all-electrical panel in IFR operation.

-DC

References:
(1) Induced lightning testing of avionics - with single stroke, multiple stroke and multiple burst [http://www.emc-partner.com/resource/pdf/a_do-160.pdf]

(2)Lightning protection for aircraft electrical power and data communication systems [http://www.microsemi.com/micnotes/127.pdf]

 

[jdeas]

Same issues

I worry about this as well. It's one reason I am building with a steam gauge backup. Most everything these days seem to have RS-232 connections around the airframe. Unless the EFIS is using an expensive isolated RS-232 driver, I would give low marks for survivability. No unit would IMHO could be guaranteed to survive a strike but those using properly isolated I/O would stand a much better chance.
In the system I am working on now there is an isolated power supply and galvanic isolators between the I/O and the system board for just that purpose.

 

[Ironflight]

Risk Avoidance

Good topic for a thread - it will be interesting to see some of the very technical folks responses on the topic!

My personal feelings are that I wouldn't want to be in ANY light single engine airplane - certified or uncertified - with ANY SEL avionics package and get hit by lightning. I have seen airplanes that were hit by lightning have significant damage, and others that were hit by lightning have no damage at all. I think you have to plan for the worst case if you are going to get hit, and frankly, I am not sure that you can protect for that.

So my answer is to avoid th risk - stay away from situations where you can get hit by lightning and have to rely on your electronics. those that read my posts know that I am comfortable flying SEL IFR with experimental EFIS units - but I generally won't fly IFR around significant areas of convection - this is another reason. I don't' want to get stuck in a situation where my only choice is to get roughed up in some significant Yellow or red areas on the XM, and lightning avoidance is also high on my list. I have seen lightning come right out the side of a severe cell and strike the ground out where the sky is clear and blue - very impressive. At least if I am VFR going around the storms, and such an event occurs, I am not depending on my EFIS to keep working.

I am afraid that I am a skeptic when it comes to "certifying" any avionics to survive a lightning strike - I fly one VERY advanced spacecraft that we won't let anywhere near convection simply because we can't convince ourselves that the fly by wire wouldn't give up the ghost.

So yup, it's an issue for me, and I deal with it by staying away from the risk. If you look at the accident statistics, you'll find very few cases where a lightning strike was the cause of the crash - there are much bigger categories that we can do something about that kill people every year....

Paul

 

[n5lp]

May be more of a chance than we think

I heard the first hand account of a pilot in a composite glider that was struck by lightning near Moriarity, NM during a contest. He was certainly in an area of convective activity (that's what makes the glider go) but he didn't see anything he thought looked threatening and had not seen any lightning.

Quite a bit of damage, including blowing up some of the composite structure and losing the canopy. Oh, it also blew the soles of the pilot's shoes off. He got back OK but his eyes were wide!

 

[aadamson]

Only one that I'm aware meets the DO-160 spec is the Chelton, both the EFIS displays and the remote mounted GADAHRS. Plus the added bonus of it running the same 6.0B software as the certified version. You might know this, but DO-160 has a number of derivatives, some do and some don't including lightning. The Cheltons all meet or exceed both..

 

[Rainier Lamers]

Only one that I'm aware meets the DO-160 spec is the Chelton, both the EFIS displays and the remote mounted GADAHRS. Plus the added bonus of it running the same 6.0B software as the certified version. You might know this, but DO-160 has a number of derivatives, some do and some don't including lightning. The Cheltons all meet or exceed both..

Our systems are designed to meet DO160 requirements where applicable (some items are not applicable due to mission/technology).
However I have to add that DO160 is quite a lax standard for many items and not all that suitable for the typical small aircraft, in particular modern composite types.
You must not forget that a typical glass installation in an airliner has very many items and meeting specs can be a nightmare under those cirumstances as much is directly related to how things are wired up rather than the individual items performance.
Our typical experimental aircraft have far fewer critical items and the wiring is a lot less - but things tend to be more critical nevertheless as things can be much closer together. For example, the airliner cockpit does not have to contend with strong RF fields caused by radio antennas in very close proximity.
Regarding lightning protection, our experience comes from a sector far removed from aviation in one of the areas in the World particulary famous for its heart stopping thunder storms (they realy are spectacular) on the South African Highveld.
As a consequence, even our little singles have oversized protection against surges.
This is one of the reasons we don't need you to switch off our avionics if you start your engine. Our stuff can handle the EMF caused by the starter motor and we have never recorded a single failure of any of our stuff related to surges (EMF and EMP) on any connections.
You would probably blow the instruments if a nearby atom bomb goes off (strong EMP), but then I don't think you would be worried about that...

Rainier
CEO MGL Avionics

 

[Rocketboy]

I am afraid that I am a skeptic when it comes to "certifying" any avionics to survive a lightning strike - I fly one VERY advanced spacecraft that we won't let anywhere near convection simply because we can't convince ourselves that the fly by wire wouldn't give up the ghost.
....

Paul

Paul,

I was skeptical as well until one dark stormy night (about 1995) when a shiney new UAL B777 decided he was tired of this long deviation along a line of severe thunder, and he announced he would blast right thru the thing. We were waiting to hear the cries from them as the fly-by-wire jet lawn-darted itself into the sea, but amazingly, they made it thru, complete with exepected pirep like "holy cow that was REALLY turbulent, lots lightning and rain" DUH!

A couple years ago I quit counting strikes after the tenth one hit us, and we were doing everything possible to avoid the weather! We had lost all COMM, HF, VHF, ACARS, SATCOM for nearly 45 minutes due to static build up and discharges/strikes. Yikes there can be nasty weather north of Buenos Aires, Argentina!

Anyway...yep the engineers (Boeing for sure) do understand it, and the certified avionics are capable of withstanding lightning strikes, repeatedly, with no damage or other ill effects. Amazing.

Here is a short vid i made last week, joking about the "storm" we were flying thru over northen Columbia (B-777-200-IGW).

What kind of spaceship you get to fly?



Bob

 

[fl-mike]

DO-160 has many categories for each section (DO-160E is the latest version). The sections are for each type of testing (vibration, ESD, lightning induced transient susceptibility, lightning direct effects, etc.) The categories (within each section) are selected based upon the location within the aircraft and the aircraft type. As you can imagine, it can be daunting to select a category that is appropriate if you really don't have a known target installation. You can narrow the categories down if you know that it will be installed in the cockpit as opposed to a wheel well for instance. The category selected will determine the test levels and waveforms used. (it is disturbing when you can actually refer to sections and categories from memory...yikes!)

Providing protection for the power and interface lines is not that difficult or expensive for the type of equipment we are discussing...if you do it on the front end of the design process. It does force you to think about these things, and that is good in itself. It is unfortunate that a lot of companies are "afraid" of DO-160 as it does instill a certain level of confidence in the robustness of a design. (and actually performing the tests can be enlightening, so to speak).

The advent of composite structures is creating additional issues for lightning induced transient susceptibility, and some companies (like Airbus) are adding tests or modifying the test levels as DO-160 may not be adequately up to date on this technology.

I know that my experiences with DO-160 testing have made my designs more robust, and I?m having fewer failures during testing on my newest designs. We typically budget about $100-120k for a suite of DO-160 tests, and hope we don?t have to re-test too many sections.

Now if you really want to see some backpedaling, ask the developers if the EFIS software was developed to DO-178B, level B.

 

[Steve Brown]

Its not about testing

........To make a long story short, it looks like avionics tested to DO-160 waveforms 3 and 4 at voltage level 3, would stand a pretty good chance (2). This basically boils down to being able to withstand 600V for 5uS and 300V for 70uS............

Performance can't be tested in. Even 600V seems like pretty wimpy lightning to me.

My 2x D10s are in a virtual Faraday cage. Lightning would have to come though the wiring - which is could. Both the power and the RS232 would need isolation of some sort.

I don't think the D10 would be a problem by itself because its surrounded by ground.

The RS232 comes from the SL30, which is vulnerable via the antenna. The power is vulnerable via the external lighting.

Need to think about this a bit --- one more thing to worry about in flight

 

[pierre smith]

The Space shuttle..

Paul,


What kind of spaceship you get to fly?



Bob

.......is what Paul is talking about. You may not know that he is very involved in the flights. Lead flight director...or something like that.

Regards,

 

[N941WR]

Only one that I'm aware meets the DO-160 spec is the Chelton, both the EFIS displays and the remote mounted GADAHRS. Plus the added bonus of it running the same 6.0B software as the certified version. You might know this, but DO-160 has a number of derivatives, some do and some don't including lightning. The Cheltons all meet or exceed both..

Funny...

There is a very nice local -8 with duel Cheltons and a Dynon D10A as backup. One day last year, while flying IFR he was hit by a bolt of lightning. Apparently the lightning toasted both Cheltons but the Dynon D10A remained fully functional. He eventually had the Cheltons replaced and continues to fly behind them but only because he has the Dynon in the panel as well.

 

[Kevin Horton]

There is a lot more to designing for lightning strikes than just choosing avionics that have passed some standardized test. The way the aircraft is wired can make a big difference too. For example, I am working with one FAR 23 aircraft manufacturer that segregates busses into "clean" and "dirty" busses. Avionics go on clean busses. Any system that has a wire that goes to something on the outside of the aircraft, or in a landing gear bay, is on a dirty bus, as those systems have a much greater chance of taking a lightning strike. I have no idea how much protection this design concept provides, but these guys will be doing lightning testing (in a ground test facility) to validate the design.

 

[Ironflight]

I agree that lots of aircraft (including light, GA aircraft) have survived lightning strikes with their avionics intact. Careful design helps with the probability of that occurring. But I have also seen Certified, high-tech airplanes with totally smoked electrical systems due to a lightning strike. It's not the successful ones that bother me.....

Paul

 

[RV10inOz]

I am ready to be shot down in flames here...... so just treat this as playing the devils advocate!

With all the weather info you guys have over there XM weather etc......... What the heck are you doing anywhere near a storm in the first place.

Read your forcasts..... Look out the window..... Geez use your XMWX and stay well clear of the bloody things. Yes I know lightning can strike many miles from a storm...... so stay plenty + many miles away! Its not that hard.

You know you do not have to track the shortest route if you plan properly.

Down under we have so few AD's so far apart, its not as easy to divert and sit it out...... you guys should never have a problem.

You are flying RV's...........Recreational Vehicles...... even if you use it for business. Its not a B767......and even they dodge storms!

Dont get struck by lightning and its not a problem.

Now beofre you start a tirade of anti Ozzie posts...... remember I do like you folk up there..... just don't try to kill yourselves!

Cheers

DB

PS: Just a thought..... when its a chance of storms around, try getting below the WX..... yes I know its nicer on top, but only if you are visual and clear of CB's, underneath you can see where the bad stuff is. Trucking along at 10,000' and in IMC is exactly how you blindly blunder into a CB that kills you.

 

[breister]

I agree that lots of aircraft (including light, GA aircraft) have survived lightning strikes with their avionics intact. Careful design helps with the probability of that occurring. But I have also seen Certified, high-tech airplanes with totally smoked electrical systems due to a lightning strike. It's not the successful ones that bother me.....

Paul

Yep - you can only let the smoke out ONCE...

 

[Maury]

You guys assume that lighting comes from T-Storms. Anytime you fly thru precipatation, you build static, which can and does discharge. My large airplanes have discharge wicks. In fact, they are MEL-able to have only one or two missing at each station. They are located on the rudder, both elevator tips and the wing tips. Metal airplanes are better than "plastic" one for taking hits. If you go to a Glasair, etc. web site, they talk about adding wire mesh to the glass parts for this very reason. I've been hit more than a few times, mostly when I was flying turbo props. It does get your attention.
Rick Maury
RV7 tail, left wing done, right wing almost there, fus/finishing kits ordered.

 

[Rainier Lamers]

Invisible lightning strikes

We have recorded quite a lot of events related to what can only be described as a "local" lightning strike that is one way or another affects our instruments.

Consider this:

Somewhere in your engine bay you have an isolated piece of metal. Perhaps it is a radiator filled with nice distilled water or a heat shield or even some part of an engine isolated with non-conductive fasteners.
The metal part in question could be anywhere on your airframe and you could have a lot of them.

On the ground with the engine off, everything works just peachy. But once in the air, sometimes or perhaps often, your avionics goes on the blink, Perhaps your EFIS crashes or restarts. You might even hear a "pop" or crackle in your intercom at times.

What gives ?

Chances are that you are having a case of static discharges. As dry air flows over your isolated metal parts charge builds up and this can reach quite incredible proportions - eventually resulting in a nice local lightning bolt.

Just as this happens, a huge current will flow - usually mostly in your aircraft's electrical grounds - the current is large enough to cause significant voltage spikes in your system and if left unchecked can give your avionics a bad time.

Sometimes it is possible to see these discharges if you run your aircraft with the cowling off at night on the ground. Do this when humidity is very low and observe carefully. Look for discharges (which are obvious) and "elms fire" - blue corona discharges around metal edges.

If you find such, attach a grounding cable to the item and the problem goes away.

Another, more unusual case we had many years ago on an ultralight with a water cooled engine. Here we had static discharges from the radiator into the airframe - but it was only partially related to airflow. The flow of the distilled water through the system acted as generator. Again, grounding the radiator solved the problem immediately.

DO160 requirements include static discharge events and in fact no real distinction is made to static discharge occurring outside the aircraft.

In defence of the Chelton panels, let me add that more complex panels that connect to many different systems are at the focus point of any electrical event and so are very vulnerable. Large currents can flow though them in order to get from one system to another (perhaps radio via the panel to the autopilot). This can create very significant havock.
Simple EFIS systems that are essentially only connected to power have a definite advantage in this case (and for this reason are perhaps good choices for backups).

Rainier
CEO MGL Avionics.

 

[Flyrod]

Its not the spider .....its the web

Rainier makes a very good point as well as many others. Most hits to electronic boxes are piped in through external connections. Are all your various connections wired to strict (certified) standards? Most likely not. Even if they are, will it be enough? That's a big question! My Cheltons are connected to no less than six different external antennas and I doubt that all these connections were wired to certified standards. If your aircraft is of composite materials, that makes your conductive web even more interesting to unusual voltages no matter how they are generated. All this does provide a strong case for steam gauge backups. Cirrus can afford the best certified engineering money can buy and I don?t think your going to see those three round dials disappear from their panel anytime soon.