Finland: "How a 737 on approach burnt a house"
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
Last edited by md80forum; 24th Apr 2016 at 09:35.