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Post crash fires

H

heinz

Active Member
Last week there was another fatal aircraft accident in my neck of the woods. A DeHaviland Beaver on floats in bad weather with six people on board crashed into the woods in a remote part of Vancouver Island. It appears that all six people survived the crash, but the pilot and one passenger died in the resultant fuel fed fire.

In the Vans RV community I personally know of three fatalities and I'm sure there are many more in both amature and small certified aircraft accidents where post crash fires have claimed lives. Not a nice way to go.

A lot of these crashes where survivable, but the major aircraft damage that resulted involved electrical components and wiring that is fractured, torn and compromised, causing shorts and arcing and fire.

In the RV community we have much expertise, skill and knowledge and are often way ahead of industry in innovation, solution and problem solving.

The problem is-----Post Crash Fires----- caused by shorted and arcing electrical wiring.

The solution is to disconnect the battery from the electrical system by incorporating a G activated switch. This could be as simple as the solid state G switch in our ELT s.

Most small aircraft have a master solenoid that is activated by providing a ground to the solenoid coil. The G switch would be connected to this terminal and in the event of a crash - say 10 Gs - would disconnect the ground connection and open the master solenoid contacts, thus removing the battery from the aircraft electrical system. ----No arcing, shorting and very likely, no post crash fire.

If there was any concern about loosing power to aircraft systems during turbulence or IFR, a simple panel mounted by pass toggle switch would solve that concern.

For some of our electronic wizards this would be a simple technical challenge that has commercial potential, but far more importantly it would save lives.

I invite comment and discussion.
 
Do we know that most of these postcrash fires are due to electrical shorts/sparks? Or by fuel coming into contact with hot engine/exhaust components, or metal that got hot in the process of being bent/scraped during the crash? Not having any idea myself, I would guess that the second sentence is more likely. Otherwise, I like your idea!
 
I share smiller's skepticism that most post-crash fires have the electrical system as the ignition source, rather than hot exhaust components, etc.

Having said that, every checklist I've ever seen for an off-airport forced landing includes turning off the master switch before touchdown. That seems like a prudent measure. That, along with turning the fuel selector valve to "off", to keep the fuel and potential ignition sources apart as much as possible.

Having said all that, designing a g-switch to disable the master relay as the OP described would not be too difficult, and could under some circumstances help if the pilot failed to turn off the master prior to impact. Still, how often the electrical system is a significant contributor to post-crash fires, I don't know.
 
Crashes

A Piper Malibu suffered a mid air around Boulder CO in the 80's. The pilot had the sense to shut the fuel off at the firewall and add full power to burn off the remainder fwf fuel. No post crash fire. He perished minutes after impact.
A Otter crashed on take off here in Alaska this summer. Two families perished in the post crash fire. The fuel is carried in the belly, same as the Beaver.
I am interested in a gizmo that will shutoff fuel at the wing/fuselage joint if the wing is torn off or some how disturbed. With the airframe fuel pump returning excess fuel, I imagine a "crash pull" handle that would isolate electrical systems, and shutoff fuel, arm fire extinguisher, activate elt and ?????
 
NASCAR Technology

I don't disagree with any of the above methods of reducing the risk of post crash fires. But I also dream of the day when aircraft fuel tanks use the same technology NASCAR uses to minimize fuel leakage when a tank is crushed. This is not nearly as big a problem in NASCAR as it once was.

This quote is from "How Stuff Works:"

"In the 1950s, NASCAR race cars used the fuel tanks from whatever street car they were based on. There were some schemes for wood reinforcements, but leaks and fires were common. Today's 22-gallon fuel tanks, also called fuel cells, have built-in safety features to limit the chance of them rupturing or exploding.

Fuel cells have a steel outer layer a­nd a hard, plastic inner layer. The fuel cell is located in the rear of the car and is held in place by four braces that keep it from flying loose during an accident. It is filled with foam, which reduces the slosh of the fuel and any chance of explosion by reducing the amount of air in the cell. If the cell does ignite internally, the foam absorbs the explosion. The car also has check valves that will shut off fuel if the engine is separated from the car."

And a little surfing yields some recent technology. Some enterprising individual should pursue adapting this technology to our RV wing tanks.

Maybe someone has already done this for RV's but I'm not aware of it. Check out this link and this link. Hmmm, they're made in Redmond, Oregon. Google maps says it's only a 3 hour drive from Redmond to Aurora, Oregon. Maybe someone can visit somebody, and we'll have a fuel bladder option soon.
 
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Fire Suppression System

I'm installing a Safecraft fire suppression system in my new 7. Fire scares me more than anything.

It is only 6 lbs and is mechanical so no power needed. I feel if it is a survivable crash it might be able to put out a FWF fire before getting to the tanks. Just might give you those few seconds needed to get out.

Cheap insurance in my book.
 
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From an old fireman.

Basics of fire. Really basic.

You need 3 things for a fire, air, fuel, and a source of ignition.

The removal of any one of these will keep a fire from happening.

The air component is something we can not eliminate.

In the case of our aircraft, the fuel is virtually always either the avgas in the tanks, or the oil in the engine-------there just is not a lot of other combustible stuff in our planes to worry about.

Lastly, the ignition component is virtually always either going to be the electrical system as stated in the OP, or the hot exhaust.

So, if you have time, and presence of mind, shut down both the fuel system and the electrical system. Not a lot that can be done about the hot exhaust.

And, dont forget to fly the plane-------the best fire prevention is to prevent the crash in the first place.
 
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Excellent discussion and something every pilot is fearful of I'm sure. Egress from an inverted RV is the thing that worries me.

One question. Does 100LL ignite by hot metal? The reason I ask, and am now ashamed to even discuss, is that I had an old '64 Buick Skylark as a kid. It had a rotten fuel line leaving the tank and there were times before I fixed it when the fuel would run onto the tail pipe and vaporize from the heat. I'm sure it was running on 87 octane. I would think 100LL would be that much more difficult to get to combust.

Just curious.
 
rv7boy said:
Mike, where is the link to the description and ordering information for the inertia activated shutoff switch? I don't see it on the above page or on the linked pages.
Click to expand...

We used this one.
https://www.pegasusautoracing.com/productdetails.asp?RecID=87
1108.JPG
 
fuel cell foam?

the Pegasus auto racing site also shows a yellow fuel cell foam that can be cut to any size and fit to fuel tanks.....albeit during construction for our tanks.

As I understand it dampens shock wave formation that causes tanks to explode, and slows leakage, and reduces combustible air/fuel vapour mixtures inside the tank. $54 for an 8x8x8" cube, E85 resistant.
 
flyboy1963 said:
the Pegasus auto racing site also shows a yellow fuel cell foam that can be cut to any size and fit to fuel tanks.....albeit during construction for our tanks.

As I understand it dampens shock wave formation that causes tanks to explode, and slows leakage, and reduces combustible air/fuel vapour mixtures inside the tank. $54 for an 8x8x8" cube, E85 resistant.
Click to expand...

The problem with this stuff is it breaks down over time. Pegasus recommends changing it every 3 years because of the fact that it'll start clogging pumps and filters.
 
I have witnessed a decathalon that nosed over on landing with full tanks. The fuel simply leaked from the caps and vents and made a nice stream entering the cowl. There was no fire. Shutting off fuel would have had no effect in this situation. I know it is a high wing, but I think a similar outflow of fuel could happen in an RV sitting on its nose. Depending on how high the tail is, the fuel might reach a hot exhaust part. Just speculating, maybe somebody has seen an RV on its nose and can comment.
 
auto ignition temp of avgas 824?F / 440?C

ConocoPhillips
001769 - Aviation Gasoline, 100 LL
Date of Issue: 23-May-2007
Vapor Pressure: 5.5-7.0 psia (Reid VP) @ 100?F
Vapor Density (air=1): >1
Boiling Point/Range: 75-338?F / 24-170?C
Melting/Freezing Point: <-72?F / <-58?C
Partition Coefficient (n-octanol/water) (Kow): No data
Specific Gravity: 0.68-0.74 @ 60?F (15.6?C)
Bulk Density: 5.83 lbs/gal
Percent Volatile: 100%
Evaporation Rate (nBuAc=1): >1
Flash Point: <-35?F / <-37?C
Test Method: (estimate)
LEL (vol % in air): 1.5
UEL (vol % in air): 7.6
Autoignition Temperature: 824?F / 440?C

Stability: Stable under normal ambient and anticipated storage and handling conditions of temperature and pressure. Extremely
flammable liquid and vapor. Vapor can cause flash fire.
 
Remember me I landed in the soccer field ? I hit that park sign going 60+mph and it sliced right into the fuel tank. Still waiting for the fuel tank to be repaired btw. But I was happy that no fire occurred. I did not get the fuel off before the landing admittedly.
 
As a child I use to always ignore the warning lables and refill my go-carts, motorcycles, lawn mower while they were hot; and I almost always spilled fuel on the exhaust. I still remember watching it boil off... I know much better now, but my experiance is telling me that the high number of post crash fires are not comming from the exhaust system.
The fuel shut-off inerita switch most cars have could work as a Master shut-off.
 
Something else to think about:
Fire resistant clothing, i.e. nomex suit and undergarments. At least do not wear synthetic such as nylon that burn well, melt and stick to skin.
Flight suits may look dorky but are cheep, comfortable and may give you the extra 60 second to get out.
 
Thanks for the input.

Transport Canada has an extensive report on--- Aircraft Post Crash Fire Statistics---

I did an experiment to see what was the more likely ignition source in this situation.

Took a tissue, soaked it in 100LL and tried to light it with a piece of red hot lockwire shorted out on a battery. It would not ignite !!!

Created a spark by striking the wires together near the soaked tissue. Instant ignition.

The automotive safety cut off switch weight is only a couple of ounces.
 
It took me a few days after reading this thread, but try as I might I could not come up with a halfway decent reason to not have this G-switch inline with the master. It will be delivered next week.
 
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