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Boost pump inertia switch

AN23

Well Known Member
Just wondering if anyone has installed an inertia switch for the fuel boost pump? It could be a lifesaver if an accident on landing rendered the pilot unconscious. I personally witnessed an aircraft accident where fuel just draining from a broken line started a fire minutes after the actual crash (there were lots of people around and both occupants escaped with minor injuries). It would have certainly been a catastrophically different result if fuel, under pressure, had been spraying around. Seems that it would be easy to do and the switches are readily available.
 
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My motorcycle has a tip over switch that cuts off the fuel, so I understand where you're coming from in concept.

however, it seems to me like the potential failure points are more problematic than the potential benefits. i.e. an ELT has an inertia switch and guys regularly set them off with aerobatics or hard landings, I don't want some random switch deciding to shut off my fuel pump when I want it on.

just curious, but in the accident you witnessed, was the broken line firewall fwd? because if not then the boost pump isn't a factor one way or the other

Not gonna discount the idea out of hand and I think it's worth discussing, but I'm going to guess that in the vast majority of cases where theres a post accident fire, it's likely caused by a fuel system rupture that can't be cured by turning off the boost pump.
 
Generally I don't like adding electrical components in critical circuits. Maybe the switch doesn't fail, but the crimp connector's wire fatigues and falls off.

But, if we are talking about a boost pump (so you have a mechanical pump as well), then I kinda like the idea.

If we are talking about the one and only pump for some EFI system... then... not so much.
 
This is the sort of switch available for race cars

Pegasus Auto Racing Inertia Switch

Seems it is a steel ball held in place by a magnet. The ball weight allows the ball to move under a "pre determined" load and this releases the switch ....It is resetable if one of your landings that you can just walk away from triggers it.

The down side is it introduces another point of failure into the circuit.
 
The probability of a failure of the G switch and the mechanical pump at the same time has to be very low. it’s probably fine and probably a good idea.
 
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I actually considered installing one of those Ford inertia/rollover switches to cut off the master contactor in my -6 about 15 years ago. I have one on my '66 GTO with EFI to cut off the fuel pumps.

But, I didn't install it because I figured going negative G's during acro could trip the switch.

Kahuna, you say you have one? Which switch is it? That Pegasus switch is the same as used on Fords starting in the 80's when they went to EFI.
 
Kahuna, you say you have one? Which switch is it? That Pegasus switch is the same as used on Fords starting in the 80's when they went to EFI.

Yes that is correct. After the Amanda Franklin accident, we reviewed it very carefully. Researched a solution. My neighbor was the crew chief for Hendricks Motor SPorts and went through their history of the various solutions they used. Then we required them on all team aircraft. Soon other air show performers began using them as well. I dubbed it the 'Amanda switch.'

I have had them on both my Pitts', both 8's, and a 3. They are flying in dozens of RV's and have been for a very long time. In line for smoke and fuel pumps.
 
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Yes that is correct. After the Amanda Franklin accident, we reviewed it very carefully. Researched a solution. My neighbor was the crew chief for Hendricks Motor SPorts and went through their history of the various solutions they used. Then we required them on all team aircraft. Soon other air show performers began using them as well. I dubbed it the 'Amanda switch.'

I have had them on both my Pitts', both 8's, and a 3. They are flying in dozens of RV's and have been for a very long time. In line for smoke and fuel pumps.

Great info, and thanks for posting that. So, just to clarify, what are the specs of your switch? Are you using that same Ford switch which Pegasus sells or something different?

And a question to anyone contemplating this: why not put the inertia switch in series with the Master switch which controls the master contactor rather than limiting its scope by only shutting off fuel/smoke pumps? If I were to crash, I'd think I'd want ALL of the electrical stuff shut off.
 
Are you using that same Ford switch which Pegasus sells or something different?

And a question to anyone contemplating this: why not put the inertia switch in series with the Master switch which controls the master contactor rather than limiting its scope by only shutting off fuel/smoke pumps? If I were to crash, I'd think I'd want ALL of the electrical stuff shut off.

Yes the exact Pegasus switched referenced.
DO NOT install this with the master. You can get false positives. During our testing, in different mount locations, we were able to trip it in flying and landing. A very firm mounting location is required.

Now, if you were not in an electrically dependent plane, and did not fly IMC, made all good landings, never needed to go around after a bounce and go, then perhaps in line with the master could be considered. Based on my experience with them, I would not under any circumstance.
 
DO NOT install this with the master. You can get false positives. During our testing, in different mount locations, we were able to trip it in flying and landing. A very firm mounting location is required.

Now, if you were not in an electrically dependent plane, and did not fly IMC, made all good landings, never needed to go around after a bounce and go, then perhaps in line with the master could be considered. Based on my experience with them, I would not under any circumstance.

Even more good info! And mirrors what I was thinking 15 years ago (I was going to switch the Master) and why I ultimately did not install one. I had assumed it would need a very stiff mount. That's what I did with my GTO.

So what I get from your comments is don't install this switch on aircraft with EFI which require the fuel pump(s) to run all the time, period. A hard landing combined with a go-around would be impossible if the fuel pumps shut off at that moment of touchdown.

Back when I was researching this, I found a company which makes aircraft-specific inertia switches which are probably good enough to switch the Master circuit. But these guys are $$$$. http://www.inertiaswitch.com/Products/Acceleration-Switches-1/Aircraft-Series-8/
 
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Thanks Kahuna! I know of at least one 8 that's going to get one installed. My son and grandson fly in it all the time. I want it to be as safe as possible!
 
Installed one several years ago in my -7. I believe I used a Ford fuel pump inertia switch. I mounted the switch on the left inside of the fuel pump housing fwd. of the fuel selector. A 1 inch hole allows me to press the reset switch on the top of the switch if necessary. No issues with this setup.
 
This is the sort of switch available for race cars

Pegasus Auto Racing Inertia Switch

Seems it is a steel ball held in place by a magnet. The ball weight allows the ball to move under a "pre determined" load and this releases the switch ....It is resetable if one of your landings that you can just walk away from triggers it.

The down side is it introduces another point of failure into the circuit.

That's the switch I installed, with electric fuel pumps (and now an electric smoke oil pump), I wanted it in place.
 
What about the opposite direction? A pressure switch that immediately starts the axillary pump with a drop in fuel pressure? I suppose one would need a bypass switch if you wanted both pumps on. Wouldn't both switches make sense?
 
Since this was moved to safety it has gone dormant. <SNIP> I want to see if I can generate a little interest in this thread again. BTW, I have ordered and received a pressure switch and an Off-On-On switch to instal next time I have the cowl off. I intend to wire the switch Off-Auto-On so I can start the engine with the switch, then go to Auto for flight and be able to turn it off if desired.
 
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