Dangers of touching the prop

[Hedley]

Yet another splinter from the tailwheel thread:

Googling "airplane takes off without pilot" gets a staggering ammount of hits

There's even a regulation about this:

http://www.tc.gc.ca/eng/civilaviation/r ... htm#602_10

Starting and Ground Running of Aircraft Engines

602.10 (1) No person shall start an engine of an aircraft unless

(a) a pilot's seat is occupied by a person who is competent to control the aircraft;
(b) precautions have been taken to prevent the aircraft from moving;

There have been an eye-opening number of hand-propping related accidents at my tiny airport.

The latest was when a pilot with a "weak battery" attempted position his prop "just so" - otherwise it wouldn't start. He moved the prop, and the engine furiously burst into life, driving across the infield - which I was certain would stop it, but no - and then it accelerated down a taxiway and started to bound up and down over the ramps and finally hit a hangar so hard it destroyed itself, the hangar doors and damaged the aircraft inside so badly it's going to need an engine overhaul in addition to airframe repairs.

The pilot claimed he "must have had a live mag". Snort. He also had the mixture in and the throttle full. I saw it hit the hangar, and it was really moving - it wasn't just at idle. We were lucky no one was hurt. I must ask, was the savings of $150 for the battery really worth all that destruction?

Less than 2 years ago, a pilot actually intending to hand-prop his champ, again had no one in the cockpit, and when it burst into life. I could hear him swearing at the top of his lungs over the sound of the engine as he hung ontoa strut and swung the champ to go nose-to-nose with a nearly-new C182 that also had it's engine running. Right next to our gas pumps. I later found parts hundreds of feet away. It was a miracle no one was hurt. Did I mention that there were 4 people in the 182?

A few years back, an AME hand-propped a Maule (not mine) which burst into life and bounded across the infield, across the runway, and went up on it's nose in a ditch.

Another weird incident - a few years back, a C210 took off by itself, late at night, and crashed in the infield. I have my suspicions about the finanacial motivation behind that "stolen" aircraft miraculously crashing itself, but again, it was only through blind luck that not one got hurt.

Another incident: a C310 running with no one in the cockpit jumped it's chocks and chewed it's way throught a shiny red pickup truck.

All of these at my tiny airport.

The data would tend to indicate that a lot of people that don't know what they are doing, are not giving aircraft propellers the respect they deserve.

[AOW]

I was taught to (on top of all the other precautions(ie parking brake, chocks, tie downs, etc.)) always hand prop with the fuel valve in the off position. There is enough fuel in the lines to start and idle for long enough to hand prop, untie, climb in and pull the chocks. If you accidentally left the throttle a little (or a lot...) to far open, the fuel will not last very long at high power, and hopefully will avoid disaster.

I appreciate your main point, however, and it is important to always assume that mags are live, and don't touch the prop unless you're prepared for the engine to start!!

[Hedley]

Indeed. Belts and suspenders.

Before you touch the prop: mags off, keys on the dashboard where I can see them from up front. Throttle idle, mixture cutoff, fuel off, parking brake on. No guarantees here - I'm just trying to stack the odds in my favour.

And yes, treat the prop as if it is "hot" because even with the above precautions, it can kick if there is a fault with the p-leads to the magnetos, or the switch.

Food for thought: everyone is convinced they had a "live mag" when a prop kicks. Uh huh. Last time you ran it up, did you do a mag check? If you get a drop on both R and L then you know that both p-leads and mags are grounding out correctly. The only remaining part in the system is the switch, which is unlikely to fail in the off position, but can happen.

There is a 1976 AD (still applicable) on Bendix mag switches which specifies every year/100 hours to do a "dead" mag check - that is, turn it to "off" briefly to check for correct grounding of both mags. I might mention that this check doesn't need to be done every day - read the AD yourself if you don't believe me - but if you must do this check, please do it at absolute minimum RPM, so that a minimal amount of unburned gas is in the exhaust when you turn the mags back on again. You can really damage your very expensive exhaust doing this. I am sure we have all heard students accidentally do this test at 1700 RPM during the runup when they select "off" by mistake, and instinctively turn it right back on again.

Free advice: if this happens to you, take your hand off the mag switch and let the engine die. Let the engine sit for a minute, to let the gas in the exhaust evaporate and clear, then restart the engine. Exhaust are very, very expensive.

Conclusion: never begrudge a few minutes spend learning about your aircraft's systems. It will pay back in spades.

[KK7]

Regarding the reg quoted above, one should note that it is not both that must be followed, but one or the other. Here's the full thing:

602.10 (1) No person shall start an engine of an aircraft unless

(a) a pilot's seat is occupied by a person who is competent to control the aircraft;

(b) precautions have been taken to prevent the aircraft from moving; or

(c) in the case of a seaplane, the aircraft is in a location from which any movement of the aircraft will not endanger persons or property.

Then:

(2) No person shall leave an engine of an aircraft running unless

(a) a pilot's seat is occupied by a person who is competent to control the aircraft; or

(b) where no persons are on board the aircraft,

(i) precautions have been taken to prevent the aircraft from moving, and

(ii) the aircraft is not left unattended.

I just wanted to point out that although you can start and run the engine with nobody inside, and this is done properly all the time, if you can at all avoid it, don't do it. Preferably, I'd rather stick an "and" there instead of an "or". Just stick someone in there, definitely someone who is in the know of how to shut off the engine. There have been people stuck in airplanes speeding across aerodromes with no idea of how to stop it. This is just something else to stack things in your favour.

I too have seen a few planes take off without anybody in them. One was a guy who had a dead battery, so decided to handprop. He *thought* it was tied at the tail with a long rope to pull to untie it from the cockpit, but it was not tied properly to secure a moving aircraft. From where I was standing, when I saw it start to move, I thought it would be short lived due to a large snow bank in front of the airplane, but the pilot grabbed the strut to try to stop it, but ended up going for a ride with the plane instead. His hanging on made the plane do a circle right into the wing of another aircraft, chopping up the wing to bits, sending shrapnel everywhere, luckily all away from this guy and anyone else around.

Lucky for the owner of the chopped up airplane, his plane was in such bad shape it wasn't flyable anymore, but got it paid out through the insurance.

[Shiny Side Up]

Before you touch the prop: mags off, keys on the dashboard where I can see them from up front. Throttle idle, mixture cutoff, fuel off, parking brake on. No guarantees here - I'm just trying to stack the odds in my favour.

Often when you see pics of military aircraft when the ground crew are about you'll see them with their hands up and visible too, something you can use here for a bit of added security, when you're near the prop with people in the plane. Its also used when operating heavy equipment and the goonspooners are near the blade/bucket.

[shitdisturber]

Before you touch the prop: mags off, keys on the dashboard where I can see them from up front. Throttle idle, mixture cutoff, fuel off, parking brake on. No guarantees here - I'm just trying to stack the odds in my favour.

Often when you see pics of military aircraft when the ground crew are about you'll see them with their hands up and visible too, something you can use here for a bit of added security, when you're near the prop with people in the plane.

We used that when aircraft were at the arming point and the pins were being removed from the weapons, ie just before takeoff. Theoretically we could use it when the last chance check was being done but I never heard of it being used as the pilots all knew there was someone in a vulnerable position and nobody was that careless.

[AuxBatOn]

Anytime the technicians are close to flight controls (flaps being a big one, stabs, ailerons), they ask us to put the hands up before they go close to these surfaces. 3000 psi of hydraulics will not stop for your arm/head and the hydraulic fill point is very close to the Trailing Edge Flaps. Also, when arming/dearming, we keep the hands visible.

[shitdisturber]

Anytime the technicians are close to flight controls (flaps being a big one, stabs, ailerons), they ask us to put the hands up before they go close to these surfaces. 3000 psi of hydraulics will not stop for your arm/head and the hydraulic fill point is very close to the Trailing Edge Flaps. Also, when arming/dearming, we keep the hands visible.

If memory serves, you can't open the door to the fill point if the flaps are set for takeoff. That being said, we never asked for hands up when topping off the hydraulics; we trusted the drivers to keep their hands away from the controls. That also being said; if I was Man 1, I watched both the pilot and Man 2 like a hawk as long as Man 2 was vulnerable. If I happened to be Man 2 doing the last chance check, I made damned certain I was never in a position where I could be clipped by a flight control and also made damned certain that any newbie/trainee knew where it was safe, and where it wasn't.

In thinking it over, I imagine the reason for the difference in how we did things then as to how they're done now is that we did two man starts instead of the single man starts you guys do.

[Posthumane]

The few times that I've had to handprop my aircraft due to a flat battery, I've had someone sitting in the seat with their feet firmly on the brakes. Most of the time it was my friend who is a flight instructor, so no questions about him being able to stop and shut down the aircraft, but one time was at a remote airfield with nobody around other than my gf. Before doing anything I instructed her about the brakes, the throttle and mixture levers, etc. and made sure she understood what to do if anything unexpected happens.

But now that you've pointed out what shouldn't be done, what SHOULD you do to start an engine when there are no facilities/people around and your battery is dead (or you don't have one)? My first instructor (on ultralights) used to reach into the cockpit and hit the starter while we were both standing beside the plane, and then hold onto the strut to keep it from rolling. I didn't know at the time if this was a bad practice or not. What can you do to effectively secure the plane for starting if you're by yourself that is still easy enough to remove while you're in the cockpit?

[Hedley]

What can you do to effectively secure the plane for starting if you're by yourself

Some people use chocks with a long rope so they can pull them into the cockpit after starting.

If you have something hefty to tie to behind you, and you are a boy scout, you can make some sort of knot that you can release by pulling on it from the cockpit.

Frankly, both of the above are pretty cheesy, unless you really know what you are doing.

As far as hand-propping goes ... there is no single "right way" to do it. It depends upon the airplane, whether or not you should stand in front of the prop, or behind it, though if you're on floats, there's really only one choice!

What I hate is when the compression strokes are all over the place - 6 cyls are like that. 4 cyls are generally nicely consistently horizontal. Some prop blades are really sharp on the trailing edge, and that hurts your hands.

I might humbly suggest that you don't stand on smooth ice when you prop. I might also suggest that you don't wear a scarf. I might also suggest that you find someone competent to give you some personal instruction.

[iflyforpie]

There's also installing a glider tow-hook and releasing it from the cockpit. This is what I plan on installing when I get an airplane with the Ernest Hemingway starter (Farewell to Arms).

Anytime the technicians are close to flight controls (flaps being a big one, stabs, ailerons), they ask us to put the hands up before they go close to these surfaces. 3000 psi of hydraulics will not stop for your arm/head and the hydraulic fill point is very close to the Trailing Edge Flaps. Also, when arming/dearming, we keep the hands visible.

It would always give me the willies doing control travel checks on big jets. Guys 30 feet up in the air on the tail with protractors or rigging boards and now you've got to move dual-redundant 3000PSI elevator or rudder PCUs through their full travel. Typically you can only see one wingtip unless you are sitting on the window sill, so everything was done with radios. And on the ol' 727, you can't reach the B system pumps or ground interconnect switch from either pilot seat.

[Dagwood]

Something I have heard is if you need to reposition the prop (ie to attach the towbar) turn the engine backwards, as the mags will not fire in reverse. Is this in fact true? Maybe a wrench turner on the forum can help.

Free advice: if this happens to you, take your hand off the mag switch and let the engine die. Let the engine sit for a minute, to let the gas in the exhaust evaporate and clear, then restart the engine. Exhaust are very, very expensive.

Another solution which I believe Cat said on here, is if the mags get turned off at high rpm, pull the throttle to idle, wait until the engine slows down enough to count the prop blades going by, then mags back to both.

[slam525i]

Good info Hedley. Every school so far has said do mag grounding checks prior to shut-down every flight. I'll keep that in mind when I (eventually) own my own.

[KK7]

Good info Hedley. Every school so far has said do mag grounding checks prior to shut-down every flight. I'll keep that in mind when I (eventually) own my own.

You can still do this every flight without hurting the engine, by checking each mag individually. It isn't as certain as doing both, but it is pretty reliable. Once in a while, do both to off with power idle, but not all the time.

[Hedley]

I say again: if you have a mag drop when you select L, and you also have a mag drop when you select R, then you know that your magnetos and p-leads are perfect, to the switch. You do NOT have a live magneto.

The only additional point of failure is the internal grounding of the switch in the OFF position, which according to the AD only needs to be checked every year/100 hrs. Checking the switch every flight instead of every year is slightly overkill!

You could also pull the cowls and check the exhaust for leaks every flight instead of every year/150 hrs as per the AD, but that would be overkill, too. If you don't check the exhaust every flight then you might have poisonous carbon monoxide in the cabin, but that's not what the AD says.

Show of hands: who here has personally found a defective switch with their testing every flight? That is, you had a drop on L, and a drop on R, but the engine kept running on BOTH because the swtich had an internal failure. I shall be interested to see the results, given the incredible over-testing.

[Cat Driver]

A propeller should be treated exactly like a gun with a hair trigger.

Never assume it will not fire when moved.

Like a gun it needs a live cartridge to fire.

The engine needs air / fuel and ignition to fire. always ensure the throttle is closed before moving a prop, if it does fire with the throttle closed you will at least not have activated a machine gun if it does fire.

Every time you turn a propeller you must be aware it could fire when moved and make sure you move it expecting it to fire.

Common sense works wonders even with airplanes.

[Beefitarian]

I have moved the prop to make it horizontal many times. I was not afraid because I usually have just ran the engine out of fuel via mixture full lean.

[iflyforpie]

I have moved the prop to make it horizontal many times. I was not afraid because I usually have just ran the engine out of fuel via mixture full lean.

A leaky primer can change that situation, just to be aware.

[Beefitarian]

I wasn't sure what it could be but sort of thought there might be something like that.

I was pretty leary the first few times. That's the problem with something like this. You don't have the engine fire and think, "Well I did everything to make it safe, no worries." then something goes wrong. I have done the mags full off check every flight also but you just never know.

One thing I wonder is how long are people leaving the mags off to get the back fire? As so far I have never got one. Was I just lucky?

I'm typically paranoid. It's kind of interesting to hear that it's probably the best course of action when touching a propeller.

[KK7]

I wasn't sure what it could be but sort of thought there might be something like that.

I was pretty leary the first few times. That's the problem with something like this. You don't have the engine fire and think, "Well I did everything to make it safe, no worries." then something goes wrong. I have done the mags full off check every flight also but you just never know.

One thing I wonder is how long are people leaving the mags off to get the back fire? As so far I have never got one. Was I just lucky?

I'm typically paranoid. It's kind of interesting to hear that it's probably the best course of action when touching a propeller.

It is okay to move the prop, but as Cat said, you must treat it like a loaded gun. Don't move it while you're standing in the prop disc/arc, and stand far enough away that should it start you're not going to be struck by it. Get ready to get your hand out of there. Some larger pistons have a special magneto set up, which the name escapes me right now (the Islander has it), where it makes it very easy for the prop to kick over if you turn it. Most companies operating Islanders have banned anyone from turning the prop unless it is absolutely essential. I know a few engineers who have seriously hurt their hands turning the props, even when the ground check on the mags passed.

For the backfire to happen on smaller piston engines, at power idle they need to be off for a few seconds, but anyone who has accidentally turned them off and immediately back on during a runup knows it doesn't take long for the exhaust to fill with fuel. I've had many a student do it, and each and every time I cringe before I take out a big stick and beat them.

[Beefitarian]

Yeah, the first time an instructor asked me to move the prop to horizontal for the other 172s to clear it taxiing past I bit my tongue but thought profanity laced questions of his sanity. After a few times a high risk habit had been added to my list of skills.

I'm pretty sure I'll be thinking of .'s word's next time I touch one and I'll be standing aside and reaching for it in a way that if I lost my balance I'd fall clear.

[Cat Driver]

I am sure your instructors clearly explained what an impulse mag is.

Treat every prop as if it has a hot impulse mag.

In other words once it moves past a certain position it is like a mouse trap except more dangerous.

[Beefitarian]

I am sure your instructors clearly explained what an impulse mag is.

If by that you mean he said, "Hey! Move the prop horizontal so the other 172s can taxi by." then you betcha.

I knew how a magnito works from riding dirt bikes and wanting to be Bob Gliddon when I was younger. That`s why I was worried about touching it.

[Cat Driver]

If you have not been taught how an impulse mag works I would suggest you understand the subject before you move the next prop by hand, because it can be deadly not knowing.

I have to be very careful how I say things here on the instructors forum because some here believe I am anti instructor.....but of course that is wrong very wrong.

[Hedley]

Some larger pistons have a special magneto set up, which the name escapes me right now (the Islander has it), where it makes it very easy for the prop to kick over if you turn it

There are two common designs for systems to help magnetos start a (certified) aircraft engine.

The most common is probably the impluse coupling, which is a spring-and-dog-leg shim which fits inbetween the magneto and the engine. At low rpm, the spring is wound up and is released just after top dead center, which spins the magneto and creates a spark. This mechanism is functional during starter cranking and during hand-propping - no matter how slowly! As soon as the RPM builds, it's a pass-through, and it allows the magneto to fire at the timed advance, usually somewhere between 24 and 28 degrees BTDC.

Not quite as common is the "shower of sparks" which is an truly ancient ignition system used on Model T/A Fords (can't remember which one - been a long time). There is no mechanical trickery, except that the left mag will have a special "retarded" points set which open after TDC. These mags will have two p-leads. Also, there will be a separate "buzz box". IIRC the old Piper Tri-pacer's had shower of sparks, and actually so do the AEIO-540 engines on our Pitts, albeit with a solid-state buzz box.

Both the impluse coupling and buzz box systems are capable of being hand-propped - I have hand-propped both systems many times, and as such both must be treated with respect. I am having trouble believing that the Islander has an especially deadly system. Either impluse coupling or shower of sparks are capable of starting an engine, or making your day go really badly if you treat either of them with contempt.

Note that there are newer, electronic ignition systems - some STC'd, some not - as well. Lasar is STC'd.