Effect of aircraft being struck by lightening

[nouseforaname]

Just wondering what the general effect would be on an aircraft having been struck by lightening whilst tied down or just parked on the ground. I am aiming this at predominantly light aircraft from a C172 to a B200 kind of bracket.

I have seen numerous aircraft on insurance salvage pages that are for sale as a result of a lightening strike (mainly in the US) whilst tied down. Does this render the aircraft completely unairworthy.? Does it cause significant structural effects or is there no measure of what damage may have been caused.?

Thanks for response in advance.

[IO540]

Apart from any airframe damage you have a mandatory shock load inspection on the engine, because the current could have "fused" some of the bearings.

So it could make it uneconomical to repair if you are talking about something at the bottom of the market.

[Pace]

I had a strike in the air over Dublin heading for Shannon several years back.
I was looking for a way through some pretty hefty storms.
A flash which was blinding hit the wing on the Seneca Five feet from where I was sitting just to the left of the Captains seat between the fuselage and left engine.
I was airways at FL100
The radios went into a mass of crackle which settled back after a few minutes, everyones hair stood on end (not fear)
Aircraft dropped 1000 feet in severe downdraughts.
Got vectored onto the ILS at Dublin and was literally chased by lightning bolts all the way down approach (not Kidding as I reckoned the aircraft was setting them off)
Landed with a closed Dublin! 14 aircraft holding for departure! Fuelling stopped.
Lots of fun but no damage signs.
Dont know what would happen with tyres in contact with the ground but should be ok.
Some people say you will find a tiny pin prick black mark where the bolt hits but never found one

Pace

[ak7274]

They don't weigh quite as much as before being lightened

[Lister Noble]

ak,you beat me to it.

[BackPacker]

You also might need a re-swing of your compass every few weeks while the magnetization of the fuselage returns to normal, slowly. Depending on how much magnetic material is in the airframe of course. Or an (expensive) de-gauss of the whole airframe.

[Charles E Taylor]

Lightning

Please read this. It will give you a real respect for lightning.

http://www.pas.rochester.edu/~cline/...t%20report.htm


Please check out the links to the various photos, they seem to work in this link.



Charlie

[Pace]

Charles

That is the problem with a lot of plastic aeroplanes which are not properly lightning protected.
Read my piece above In a Seneca Five! Direct hit on the wing and no damage whatsoever.

Pace

[Mechta]

The meeting between an ASK21 glider and a lightning bolt was recreated on a BBC '999' programme some years ago. Here is the (non-technical) description of the incident by the passenger: Powered by Google Docs

Getting composite aircraft parts qualified for larger aircraft can be a nightmare, as electrical bonding of any metallic inserts is a must, and coatings and joints have to last the anticipated life of the component if lightning protection is to be maintained. Some components have a fine metal mesh moulded in, but this must be properly earthed too.

[chrisN]

The UK AAIB report can be found here of a glider destroyed by lightning:
http://www.aaib.dft.gov.uk/cms_resou...pdf_500699.pdf


From the AAIB report re GRP etc: "These materials are electrically
non-conductive." . . . "In aircraft or gliders constructed from a
non-conducting material such as GRP, the lightning arc is likely to attach
to the extremities of any linked conducting components within that
structure".

Electrical conduction through the metal parts, mainly I think the aileron circuit, caused the aircraft to disintegrate – pressure resulted from the high current heating the air and blew the fuselage apart.

Chris N
[posted before I saw the one above - took me that time to seek the link!]

[Charles E Taylor]

Mechta

Both are the same report, the direct AAIB link does not have the pictures which are essential to give a good understanding of this.

Given that the estimation that this strike was a factor of 8-9 higher than lightning certificated aircraft are currently required to tolerate with minimal damage, it should at least give metal aircraft operators some concern.


Be careful with lightning.


Charlie

[Pace]

Charlie

My storm was bad enough to close down Dublin airport and to stop all refuelling till it past over.
From where I sat the strike seemed pretty hefty With NO damage to the metal aircraft ( A Seneca )
Composites do create a problem
Show me such a report on an all metal aircraft?

Pace

[ericferret]

Some of the larger all metal aircraft suffer from lightning strikes on a regular basis. For some reason the 737-700 seems particularly prone.

One UK -700 going in to heavy maintenance was found with over 40 burns on the fuselage crown skins. Usually they are on rivets which require replacement, if the rivet holes are damaged beyond limits then larger repairs are required. As the aircraft are pressurised this makes even small amounts of damage a serious issue. A regular lightning strike area on the 737 series is the wing tip navigation lights. Not unusual to find steel screw heads totally burnt off.

One composite aircraft I work on is subject to regular bonding checks as the tail is almost totally composite. Keeping the bonding figures within limits is time consuming and difficult.
They usually are out of limits until all the bonding points are cleaned up.

There is a photo of one of Helikopter Services Super Puma's which had a lightning strike on a composite main rotor blade. The photo shows the chief engineer at Bergen with his head through the hole!!!!

[Charles E Taylor]

Pace

Be as carefree or careful as you wish. But at least be aware.

Just a quick look on the net resulted in this.


The following is a list of the fatal crashes since 1963 involving lightning strikes on aircraft weighing more than 5.7 tons:

• 27/02/2002, Let 410 (twin-engine turbo prop), Comoros Islands, following a lightning strike, the artificial horizons and gyro compasses malfunctioned. The pilot lost control of the aircraft, one person onboard died.
• 10/1/2001, Merlin IV (twin-engine turbo prop), Mediterranean Sea, total failure of the electrical systems, all 10 people onboard died.
• 08/02/1988, Metro III (twin-engine turbo prop), Germany (Kettwig), total failure of the electrical systems, all 21 people onboard died.
• 24/12/1971, Lockheed L-188A Electra, combination of lightning and severe turbulence, all 9 people onboard died.
• 08/12/1963, B707, Philadelphia (USA), fuel tank explodes after a lightning strike, all 81 people onboard died.

From

NLR-ATSI: Lightning strike reportedly downed Ethiopian Airlines jet





Charlie

[Pace]

How often are aircraft struck by lightning?

It is estimated that on average, each airplane in the U.S. commercial fleet is struck slightly more than once per year. In fact, aircraft often trigger lightning when flying through a heavily charged region of a cloud. In these instances, the lightning flash originates at the airplane and extends away in opposite directions. Although record keeping is poor, smaller business and private airplanes are thought to be struck less frequently because they usually do not adhere to rigid schedules.

Does lightning cause aircraft to crash?

The last confirmed civilian plane crash that was directly attributed to lightning in the U.S. was in 1967, when lightning caused a catastrophic fuel tank explosion. Since then, much has been learned about how lightning can affect airplanes, and protection techniques have improved. Airplanes receive a rigorous set of lightning certification tests to verify the safety of their designs.

What happens when an aircraft is struck by lightning?

Although passengers and crew may see a flash and hear a loud noise, nothing serious should happen because of the careful lightning protection engineered into the aircraft and its sensitive components. Initially, the lightning will attach to an extremity, such as the nose or wing tip. The airplane then flies through the lightning flash, which reattaches itself to the fuselage at other locations while the airplane is in the electric "circuit" between the regions of opposite polarity. The current will travel through the conductive exterior skin and structures of the aircraft and exit off some other extremity, such as the tail. Pilots occasionally report temporary flickering of lights or short-lived interference with instruments. We have heard reports of the activation of cabin oxygen masks; no doubt frightening for the passengers.

How is an aircraft protected from lightning?

Most aircraft skins are made primarily of aluminum, which is a very good conductor of electricity. By making sure that there are no gaps in this conductive path, the engineer can assure that most of the lightning current will remain on the exterior skin of the aircraft. Some modern aircraft are made of advanced composite materials, which by themselves are significantly less conductive than aluminum. In this case, the composites are made with an embedded layer of conductive fibers or screens designed to carry lightning currents. These designs are thoroughly tested before they are incorporated in an aircraft.

Modern passenger jets have miles of wires and dozens of computers and other instruments that control everything from the engines to the passengers' music headsets. These computers, like all computers, are sometimes susceptible to upset from power surges. So, in addition to the design of the exterior of the aircraft, the lightning protection engineer must assure that no damaging surges or transients can be induced into the sensitive equipment inside of the aircraft. Lightning traveling on the exterior skin of an aircraft has the potential to induce transients into wires or equipment beneath the skin. These transients are called lightning indirect effects. Problems caused by indirect effects in cables and equipment are averted by careful shielding, grounding and the application of surge suppression devices when necessary. Every circuit and piece of equipment that is critical or essential to the safe flight and landing of an aircraft must be verified by the manufacturers to be protected against lightning in accordance with regulations of the FAA or a similar authority in the country of the aircraft's origin.

The other main area of concern is the fuel system, where even a tiny spark could be disastrous. Therefore, extreme precautions are taken to assure that lightning currents cannot cause sparks in any portion of an aircraft's fuel system. The aircraft skin around the fuel tanks must be thick enough to withstand a burn through. All the structural joints and fasteners must be tightly designed to prevent sparks as lightning current passes from one section to another. Access doors, fuel filler caps and any vents must be designed and tested to withstand lightning. All the pipes and fuel lines that carry fuel to the engines, and the engines themselves, must be verified to be protected against lightning. In addition, new fuels that produce less explosive vapors are now widely used.

Radomes are the nose cones of aircraft that contain radar and other flight instruments. The radome is an area of special concern for lightning protection engineers. In order to function, radar cannot be contained within a conductive enclosure. Protection is afforded by the application of lightning diverter strips along the outer surface of the radome. These strips can be solid metal bars or a series of closely spaced buttons of conductive material affixed to a plastic strip that is bonded adhesively to the radome. These strips are sized and spaced carefully according to simulated lightning attachment tests, while at the same time not significantly interfering with the radar. In many ways, diverter strips function like a lightning rod on a building

Private general aviation planes should avoid flying through or near thunderstorms. The severe turbulence found in storm cells alone should make the pilot of a small plane very wary. The FAA has a separate set of regulations governing the lightning protection of private aircraft that do not transport passengers. A basic level of protection is provided for the airframe, fuel system and engines. Traditionally, most small commercially made aircraft have aluminum skins and do not contain computerized engine and flight controls, therefore they are inherently less susceptible to lightning. Numerous reports of non-catastrophic damage, such as to wing tips, propellers and navigation lights have been recorded.

A growing new class of kit-built composite aircraft also raises some concerns. Because owner-assembled, kit-built aircraft are considered by the FAA to be "experimental," they are not subject to lightning protection regulations. Many kit-built planes are made of fiberglass or graphite-reinforced composites. At Lightning Technologies' laboratory, we routinely test protected fiberglass and composite panels with simulated lightning currents. The results of these tests show that lightning can damage inadequately protected composites. Pilots of unprotected fiberglass or composite aircraft should not fly anywhere near a lightning storm or in other types of clouds, because non-thunderstorm clouds may contain sufficient electric charge to produce lightning. NASA has a Small Business Innovation Research project for the development of cost-effective lightning protection for kit-built aircraft. Conducted by Stoddard-Hamilton Aircraft, Inc. and Lightning Technologies, Inc., the program designed and tested lightning protection against severe in-flight strikes for Stoddard Hamilton's fiberglass composite Glasair III LP, a small high-performance, kit-built aircraft..

Hope this explains why in properly lightning proofed aircraft lightning should not be a problem.
Pace

[chevvron]

Only time I've seen the effect was from an air strike on a C152. It hit one wingtip, travelled across the airframe, and literally blew the opposite (plastic) wingtip off.

[UV]

Flew under a towering Cumulus (not CB) in a Falcon with 2 Hawks in close formation. The strike went though all three of us!

[Pace]

Pilots of unprotected fiberglass or composite aircraft should not fly anywhere near a lightning storm or in other types of clouds, because non-thunderstorm clouds may contain sufficient electric charge to produce lightning.

With my own lightning strike experience it explains to me why I seemed to be chased down the approach into Dublin by flashes, as I suspected the aircraft was setting them off.
The above snippet explains that it doesnt have to be a CB to experience a lighning strike other clouds with enough electrical charge will do so.
It warns of the danger of composite aircraft especially those that have not had full lightning protection.
This is relevant especially to gliders as they tend to circle around CBs towering cumulus or large cumulus looking for lift yet they are the most vulnerable to lightning strikes.
My own in a Seneca only caused temorary loss of the radios. It appears that if you have a metal aeroplane with a metal prop you are fairly safe if you fly a composite or part composite part metal beware if it has not been properly lightning protected.

Pace

[Charles E Taylor]

Lightning

I operate from EGSH.

In July 2002, 11 people lost their lives in a Helicopter operating from this base, this event was attributed somewhat to lightning.


The rather short AAIB report can be found here.
http://www.aaib.gov.uk/cms_resources.cfm?file=/dft_avsafety_pdf_503164.pdf

This aircraft was fully lightning certified, inspected and approved to all of the required standards. After the lightning strike the blade in question underwent further inspection by the manufacturers.

There is an increased appreciation of the effects of lightning, at this airfield at least!

This rotor blade was manufactured in March 1981. In 1999 when fitted to Sikorsky S76A G-BHBF
it was damaged by a lightning strike (see AAIB Bulletin 3/2001). At that time the blade had
accumulated 8,261 hours usage. The blade was returned to the manufacturer for assessment where,
following inspection, it was repaired and returned to service. Neither the thermal damage to the
spar nor the manufacturing anomaly were detected during this inspection. At the time of the
accident, the blade had accumulated 9,661 hours usage. The airworthiness limitation life of the
blade is 28,000 hours.
The AAIB and the helicopter's manufacturer are of the opinion that the electrical energy imparted
by the lightning strike in 1999 exploited the anomaly that was built into the blade at manufacture
and damaged the spar.

Safety action
On 24 July the aircraft manufacturer issued Alert Service Bulletin (ASB) 76-65-55. The purpose of
this ASB was "To remove from service any main rotor blade identified as having been damaged by
a lightning strike". A modified version of the ASB (76-65-55A) was issued the next day. The
modifications related to the accomplishment instructions and did not alter the purpose of the
original ASB. The modified ASB was subsequently mandated by Emergency Airworthiness
Directive 2002--15-51 issued on 26 July by the Federal Aviation Administration.

Nature, the only “Superpower” can be a formidable adversary.


Take care.




Charlie.

[Pace]

The AAIB and the helicopter's manufacturer are of the opinion that the electrical energy imparted
by the lightning strike in 1999 exploited the anomaly that was built into the blade at manufacture
and damaged the spar.

The blade was faulty at manufacture and as such may not have been lightning protected.
It is not clear whether they blame the lightning strike or the fault at manufacture which was exploited by the lightning strike.
I stress that on average every airline flying in the USA experiences more than an average of one strike per year.

Pace