Let's hear from the old schoolers

[Lead Sled]

Why kind of airplane were you in, lead sled.

An Astra.

LS

 

[Princedietrich]

I should bring this up to my boss. He said I would get a raise when pigs fly.

 

[Spooky 2]

Here's a link to a 1960 article on the subject: http://www.time.com/time/magazine/article/0,9171,894885,00.html

I don't believe there's ever been a case of lightening or a static discharge igniting Jet A, though there have been cases of lightening causing aircraft losses (and explosions) when fueled by Jet B (which is cut with gasoline, vs. purely kerosine).

So far as the danger itself; St. Elmo's can progress from a harmless display to a static discharge fairly quickly, and can certainly cause structural damage, though generally not to the degree of a lightening strike. A lightening strike, on the other hand, may cause damage ranging from a small burn hole going in and going out, to blown off radomes, blown out electrical panels, failed avionics, etc. A lightening strike has a higher potential to cause a fire or explosion.

St. Elmo's fire isn't actually fire, and nothing is burning. It's an electrostatic display which doesn't represent necessarily an increased temperature. In aircraft fueled with Jet A, the fuel tank generally contains a fuel/air mixture which is not conducive to a fire or explosion, especially from static discharges. This is a different matter with cut fuels such as Jet B or JP4. 100LL would be much more likely to ignite than Jet A.

I made a flight one night during a period of electrical activity, in a Seneca II. While I've seen St. Elmo's at higher altitudes often, I've not seen it often in light GA type aircraft. In this case, around eight or nine thousand feet, the propellers glowed blue green, and purplish and yellowish sparks spayed off the fuel caps, and other plastic non-conductive surfaces, including the windshield. Sparks danced around insidethe cockpit and across the windscreen. The propellers took on a neon caste, particularly around the tips, leaving two glowing circular arcs on either side of me. I quit looking outside and turned up the cockpit lights in case of a static discharge, but that didn't happen. It went away. My imagination certainly turned to the possibility of a fire or explosion with the active display of sparks spraying off the fuel caps, but nothing occured.

St. Elmos can signifiy ionization of the airflow around an aircraft, which can in turn form a pathway for lightening, or for a static discharge. With the presence of a discharge or lightening strike, the potential for a fire or explosion is escalated.

The USAF lost a C-130 and a KC-135 to lightning, as well as a F4 and a F16. Internationally a 707 was downed in 1963 and a 747 in 1976 as a result of the same, involving explosions or fires caused by the lightening. In each case, the aircraft was using a cut fuel.

There's never been a verified case of an explosion or fire in flight with Jet A, based on lightening or a static discharge. There have been many cases of engine flame-outs during such events, however, and other types of damage such as structural burns, blow-outs, melting, etc, do occur. I've had holes burned through flaps, elevators, and even propellers, and blow-outs in radomes (usually isolated to small semi-circular burns or blow-outs about a half inch to three quarters of an inche in diameter, in the shape of a thumb or crescent. I've also had melting on pitot tubes, stall/AoA vanes, etc.

Might have to call you on this last paragraph regarding lightening causing a catasprophic explosion on an aircraft. Back in 1963, Pan Am lost a B707-100 (N709PA) while it was holding at 5,000 prior to landing at either PHL or BWI, can't recall which. The left wing exploded when fuel vapors were ignited in the outer aux fuel tank vapor bay, thus causing the crash. The aircraft was fueled with Jet A but also contained a small amount of JP4 which obviously did not help matters, however, in the official accident report this mixture of fules was discounted and not found to be a contributing factor. A lot of new information has been generated over the last fourty years so one might assume that this new data would give some creedence to the fuel cuts used in this event. A greater amount of evidence was the suspicision that the lighten strike was a positve strike and thus significantly stronger.

I have both lightening strikes and massive discharges and it is frequently hard if not impossible to tell which has created the spectacular effects.

 

[avbug]

The 707 was fueled with Jet B mixture (cut fuel with gasoline, not straight kerosine); it was the one I mentioned in my comments. An Iranian B747 was lost during fuel tank explosion after a lightening strike, too...but was also using a cut fuel. A Lockheed Electra experienced an explosion following a lightening strike...cut fuel.

No history of aircraft exploding when fueled only with Jet A.

Static discharges and lightening strikes appear similiar in flight, though the damage left over usually is more localized in a lightning strike, whereas a static discharge usually has multiple points around the aircraft where damage has occured.

 

[Spooky 2]

I was probably editing my comments when you were sending me your thoughts on this subject. The fact that this cut fuel load was not a considered a factor in the final accident report is revealing for the time period in which the accident happened. The biggest change to operating procedures was the addition of static wicks to aircraft.

 

[avbug]

The Iranian B747 was also destroyed as a result of a failure of the aiframe and bonding to properly transfer the current. I've seen a lot of static wicks blown apart and/or melted when handling that electrical transfer; a small, but vital sacrifial part on the airframe.

I flew an airplane that experienced two static discharges of a significant nature, both of which did damage to the airframe. When the incidents occured, separated by a year, the company initially blamed me for operating too close to thunderstorms. I wasn't. I didn't find out until nearly a year after that, from someone in the training department, that they company had found the entire aircraft improperly electrically bonded. Every static wick and bonding surface had non-conductive paint beneath it. The company tried to hide that fact and settled for blaming the pilot.

 

[UALX727]

Dude, that's some messed-up stuff....

 

[Axel]

Regarding the "Pig Strike" report: From AVweb

Snake Strike

I read your article about flying snakes with interest (NewsWire, May 16). And I know the answer to everyone's subsequent question: Yes it's happened -- a mid-air snake-strike!
In one of the weirdest encounters I've ever heard of in aviation, a colleague of mine suffered a snake-strike flying a BAe-146 on final approach into Charles de Gaulle [Paris, France]. In this case, however, the hapless reptile wasn't truly flying itself; a heron had picked it up and made a flight path conflicting with the aircraft. At the last minute it panicked, turned away and dropped the snake, which struck the forward, left-hand side of the fuselage before being ingested through the #2 engine (this being deduced by the presence of the remains of the animal on the fuselage).
Consequently, the crew was forced to make a snake-strike report! And they say stranger stuff happens at sea.
Love reading AVflash.

 

[tomgoodman]

Hitting things

Heard a story about a "person strike" involving a skydiver and a light airplane. Supposedly, his chute got tangled in the elevator, causing a crash, but he cut loose, deployed his reserve chute, and survived.

 

[Lead Sled]

The most "compromised" I've ever been after hitting something involved insects. 30 years ago when I was flying the Grand Canyon, I flew through a swarm (flock, herd, gaggle, or large group) of migrating Monarch Butterflies on descent into Las Vegas. It was a mess - the oil coolers on both engines were plugged and the windshield was 95% smeared with butterfly guts.

LS