Finland: "How a 737 on approach burnt a house"

[md80forum]

A Norwegian 737 approaching Helsinki on Apr 23 after its flight from London-Gatwick triggered a cold condition lightning strike, that first hit the aircraft and then a wooden house on ground in Espoo, west of the airport. The house in Lippajärvi community caught fire with extensive damage.

"I don't know if it is common knowledge elsewhere in the world, but we have seen how airplanes in very cold conditions may trigger lightning", says meteorologist Hannu Valta at the Finnish Meteorological Institute to newspaper Ilta-Sanomat. "In Summer the electric potential grows strong enough to release lightning by itself, but at this time of year, the lightning is lazy and only an airplane may trigger it".

Mr. Valta says scientists are uncertain whether the metal structure of the aircraft, or ice crystals formed by exhaust gases, are the main trigger.

At the time of the incident the CB base according to metars was at 3,000 ft with ground temperatures at 4°C and dewpoints at around zero. According to FR24 data the aircraft was on final at 2,500 ft. Similar incidents have been noted in Finland in early Spring with aircraft flying below snow or hail clouds. This incident also triggered a heavy hail shower after the lightning strike.

In Finland, CB and lightning monitoring is done both by professionals and extensively as a popular hobby with numerous lightning detecting devices and networks. This made it possible to confirm that the same, rare strike hit both the 737 and ground.

On the same day only three lightning ground strikes were detected. Unbelievably, also another strike about one hour earlier had hit another Norwegian 737, this one on approach from Barcelona.

Relevant metars:

EFHK 231020Z 01007KT 330V080 9999 -SHRA SCT025 BKN030CB 04/01 Q1005 TEMPO 7000 SHRA
EFHK 230950Z VRB03KT 9999 VCSH BKN025 SCT030CB 05/00 Q1005 TEMPO 7000 SHGS

[finncapt]

Interesting.

I live under the approach to 22L, about 10 nm out.

We had two ligtning strikes yesterday, the first (fairly close) took the power out, it was off for about an hour.

The second hit the telephone wire about 10 metre from my house and fried the modem - had to buy a new one!!

There was heavy hail at the time.

It scared the beejesus out of me as the flash and enormous bang were almost instantaneous.

My wife was on the terrace taking a photograph, of the hail, and she was probably only 5 or so metres from where it struck the ground - to say she was somewhat scared is probably an understatement.

I have been struck several times in aircraft but that, in retrospect, pales into insignificance.

[sabenaboy]

As long as you don't prove that there wouldn't have been a lightning strike without the plane passing there it proves exactly nothing.

I'm not saying it's not possible. I'm just saying that the claim the aircraft caused the strike isn't very scientific. If there's a Cb, you can expect lightning, regardless if there's a plane around or not.

[golfyankeesierra]

They probably mean AIL, Aircraft Induced Lightning. That is completely different from the usual lightning associated with a summer Cb.
It is especially prone to happen with cold polar air over relatively warm water masses in winter, like AMS and the Great Lakes, and probably Finland is geographically similar.
Interesting study here:The Prediction and Occurrence of Aircraft Lightning Encounters at
Amsterdam-Schiphol Airport (http://www.enu.kz/repository/2009/AIAA-2009-553.pdf)

[DOVES]

Oh Dear!
I love flying in cbs.
If I do not do it at least once a month, it comes a withdrawal syndrome to me.
Seriously: You won't believe it, but in fifty years I have met only a lightning.
That bad! It was like I was hit by a cannon
Was it because I was lucky?
Safe flights (and avoid Thunderstorms!)

[pattern_is_full]

Ben Franklin didn't even need a 737 - he managed to "call down the lightning" by just flying a kite!

http://all-len-all.com/wp-content/uploads/2014/06/Franklins_experiment.jpg

Anyway, an interesting event, and I suspect the theory is correct, in the right circumstances.

[Guest 112233]

The Temperatures were at a guess similar to those posted previously and a Boeing 777-200 leaving Cambridge after maint, I would imagine;triggered an almighty double lightening strike that I was almost underneath at about 2.6 NM DME Cambridge.

Wore the Tea Shirt and felt the Bang !

[finncapt]

This has quite got my interest.

As mentioned earlier, my house is "on the ILS" to 22L and thinking back I may have experienced a similar incident a few years back.

October? time, large clap of thunder which split a tree in my forest - caused it to drop and there was a longitudinal burn mark along the split - only clap of thunder that day.

Thought nothing of it at the time and I have never heard of the hypothesis of "aircraft triggered lightning" before.

Perhaps I should move!!

[twochai]

Some years ago (probably 40!) I remember a lightning strike in a turbo-prop descending into Toronto YYZ across Lake Ontario in very benign weather conditions - no radar returns, light ice crystal conditions at around 4,000' but nothing particularly remarkable.

The airframe took some damage when the strike entered through the cockpit roof above the windshield and exited the tailcone, frying the combination taillight, rotating beacon and tailcone into a molten mass of plastic and metal. The magnetic compass was also seriously affected and the aircraft eventually had to be degaussed somehow.

An interesting thread.

[RIGHTSEATKC135]

My Master's thesis included a large amount of information regarding N709PA, Pan Am Flight 214, en-route from Baltimore-Friendship, to PHL, on the evening of December 8th, 1963, when it was struck by lightning (in midair) near Elkton, MD, and crashed - killing all aboard.

The (full version of the) CAB report listed three pages of info regarding "the possibility of aircraft induced electrical activity", which may be of interest to some of our more science-minded forum members.

A very well researched .PPT presentation about the tragedy can be viewed here (https://www.youtube.com/watch?v=5KulaSksiRc).

[lederhosen]

I wonder if there is a link between indicated air speed and getting struck. In the old days (cheaper fuel) we used to fly a lot faster lower down and most of my strikes were over 300 knots indicated in cloud. Of course going slower makes it easier to avoid the weather so maybe that would explain it.

[Loose rivets]

I don't think there was an aircraft involved, but this stunning home, on its own mini-mountain in Texas, was there one moment and gone the next. The sheriff's daughter happened to be looking straight at it when it was hit. The core of the house became an orange ball.

In some places the stone had melted.

There's a certain irony about this. We'd always said if the ice caps started to melt (more) we'd retreat there as it was 1200' above sea level.

http://img.photobucket.com/albums/v703/walnaze/PpruNe/Firedamages2.jpg (http://smg.photobucket.com/user/walnaze/media/PpruNe/Firedamages2.jpg.html)

[Exnomad]

Surerly a large chunk of metal flying close to a high voltage source must encourage strikes.
I have been a passenger when the pilot has taken care to avoid a cunim on his route

[andytug]

From what I remember from my high school physics lessons, electric fields (such as inside thunderclouds) concentrate at points, such as the tops of trees, high buildings, pylons, carbon fishing poles etc. Aircraft are metal and similarly pointy (wing tips,tail for example) so I guess would also attract lightning? That's where you see St.Elmo's Fire,too?

[silvertate]

They probably mean AIL, Aircraft Induced Lightning. That is completely different from the usual lightning associated with a summer Cb. It is especially prone to happen with cold polar air over relatively warm water masses in winter.


Not sure about that. We came out of MAN UK one warm and humid day, and although the air was electric there were no thunderstorms. And then we had a big strike, that knocked off two static wicks. ATC confirmed that was the only strike they had seen all day, and so this must have been aircraft induced.

[Nialler]

Interesting. From an insurance perspective would it change the incident from an act of God to one caused by a human agency?

[Lazerdog]

Hopefully someone will capture of a photo of one of these events. There is lots of static potential in dry cold air and I wonder if the exhaust of an airliner might cause some type of "collector trail" for a discharge to occur. Interesting stuff. I did lightning mitigation work for an avionics company years ago and saw some very strange effects on high speed film of strikes on an F-106 NASA aircraft we studied.