Hand Propping and Airplane Dangers

[Broomstick]

In my on-going saga of flight training, I've alluded to hand-propping airplanes to start them instead using an electric starter. I've made frequent reference to hazards of doing so, without having described any Bad Things in thorough detail. This is because, at least in part, these Bad Things have not happened in my presence, and I can only hope they never do.

The following is an image well-known among pilots on the internet, and is certainly worth a thousand words. First, a little backstory:

Once upon a time, a man decided to handprop his airplane while it was still in the hangar. Normally, you handprop away from other solid objects, but for some reason he did this inside. It is also suggested that you procure the assistance of at least one other person, preferably another pilot who is familar with the risks and safety procedures, when handpropping. This is not mandatory, and the gentleman in question did not ask for or seek help. This is not a problem IF you secure your airplane so the airplane will positively stay put, usually by chocking the wheels although I've seen people tie down the tail. Clearly, from the result, this person neglected to take this precaution. He got the airplane started, alright, but then it got away from him and proceed to wander off, on its own, without human aboard. Since it was in a crowded hangar, it very soon encountered another solid object. This was the result:



I would just like to point out that, most likely, the engine was at idle when this occured. A prop at full throttle would be even more devastating.

And now you know why I both respect and fear airplane propellers.

[aerius]

It's amazing how the plane was so neatly sliced up by the prop. The part that somewhat baffles me is how he managed to keep his body parts attached when the plane got away from him and did that.

[Broomstick]

Proper handpropping technique involves stepping back and away as you pull the prop blade. At least he got that part of the procedure correct.

I've been trying to estimate how long it took for the prop to make those slices. Assuming a starting rpm of 800 to 1000, and counting 23 slices, that damage was done in between 1.38 and 1.73 seconds by my reckoning. Anyone who cares to is free to check my math.

Yet another illustration of how when things go wrong in aviation they go wrong very quickly.

[Surlethe]

I've been trying to estimate how long it took for the prop to make those slices. Assuming a starting rpm of 800 to 1000, and counting 23 slices, that damage was done in between 1.38 and 1.73 seconds by my reckoning. Anyone who cares to is free to check my math.

Your math is good.

Shit, that mistake looks expensive; how much did it cost him? What sort of penalties get slapped down?

Also, don't let Chardok see this thread.

[Soontir C'boath]

Maybe he didn't like the owner/plane.

I've been trying to estimate how long it took for the prop to make those slices. Assuming a starting rpm of 800 to 1000, and counting 23 slices, that damage was done in between 1.38 and 1.73 seconds by my reckoning. Anyone who cares to is free to check my math.

Damn, that's fast.

[Broomstick]

Shit, that mistake looks expensive; how much did it cost him?

Well, the destroyed airplane is a twin, meaning expensive. The airframe is totaled. The prop blade crossed the mid-line multiple times. I can tell from the tail/rudder sag that the prop blade reached the rudder cables and severed them on the right side, so it's through the supporting, weight/stress bearing structures. You can't fix that. I'm not sure, but if that twin is a Piper and I'm seeing what I'm thinking I'm seeing the prop might also have nailed the right wing spar and the engine. So those are junk, along with the right main gear. Basically, you can probably salvage the left wing and maybe some of the avionics.

That's in excess of $100,000 USD damage. Exact figure would depend on the age of the airplane in question, plus if any expensive avionics like a Garmin 430 GPS or the like were installed on the right hand side of the cockpit and trashed. Damages could be $200,000 or more if it was new or relatively new airplane with a really good equipment package on board.

What sort of penalties get slapped down?

This happened in Australia, and their regs are somewhat different than those of the US. However, I'm positive there's a "reckless use of an aircraft" penalty involved here. Liability for damages. Almost certainly suspension of license and flying privileges. Clean up costs - if you look under the right wing there is spilled fuel and engine fluids, and from my past experience with/research of prop accident aftermath there were probably debris flung at high speed through the hangar which will likely be embedded in walls, ceiling, floor, and other aircraft that do not appear damaged in this photograph but may have shrapnel removal issues. This airplane is the most dramatic damage, but it's unlikely it's the only damage in the vicinity.

[Broomstick]

I've been trying to estimate how long it took for the prop to make those slices. Assuming a starting rpm of 800 to 1000, and counting 23 slices, that damage was done in between 1.38 and 1.73 seconds by my reckoning. Anyone who cares to is free to check my math.

Damn, that's fast.

At full throttle, the damage would have occured in .53 seconds. This is not the worst-case scenario.

Amazingly enough, people have survived being hit by a moving prop. It's rare - you have better odds of a surviving a mid-air collision than contact with a moving propellor. Not a recommended experience.

And the man responsible DID get out of way in time. If he hadn't... well, the resulting photograph would probably not have been passed around as freely. I mean, take a blender, turn it on "high", and drop in a carrot.

Even radio control models can be extremely hazardous, as they, too, use propellors. Fingers removed and such. And there was an instance last year of a rc model helicoptor taking the leg off its owner/pilot. Sure, flying toys are fun, but mishandled they're dangerous.

In case you were wondering - no, jet engines aren't any safer, nor are turboprops.

[Broomstick]

Here's a slightly different angle on the problem:



The source for this photo identifies it as a Piper Seminole and mentions that a dozen other aircraft were damaged in this accident. An accident that occured in less than a minute, start to finish.

Here's yet another view:




Here's another boo-boo - Cessna Skyhawk vs. Cessna Caravan in Canada. It looks like the prop in this case may have missed critical structures. In other words, the Caravan might be repairable although yes, it's an expensive mistake. This was, again, another bungled handpropping where the airplane got away.




Here is a gentleman demonstrating one technique for handpropping a small airplane (a Mooney-mite one-seater). Note the serious look of concentration. He is standing behind the prop, so if the plane moves forward it will move away from his body. This also allows him to rapidly climb into the cockpit to reach the controls. To be honest, I don't like how far he's leaning forward, I hope that's for posing, not actual propping.




This is handpropping from the front. The pilot has just completed one pull of the blade and has stepped back and away in good form.



And another one:




This guy is asking for a decapitation - he's leaning in, towards the prop! Bad form! Bad pilot!

[Broomstick]

More fun facts about that awesome up-front meatslicer:

At full throttle/take-off, the tips of the prop blades approach Mach 1, the speed of sound. That's one reason departing aircraft are so noisy - a lot of the roar is actually the propellor, not the engine.

Swinging around at high speed, the force attempting to pull the blades out of the hub and away is somewhere between 10 and 20 imperial tons (depending on specific engine, prop, and other considerations). If the connections fail, this is a possible result:


As you can plainly see, a departing prop blade punched through the fuselage with no problem whatsoever.

This is normal "blade erosion". The black area is paint, the lighter area is bare metal where the paint has been eroded. This erosion is caused simply by the friction of the prop moving through the air, which is why it's always more noticable by the tips, where the prop airspeed is greatest. Flying in precipitation of any sort will accelerate this wear. A definite nick is visible where something larger than an air molecule or water drop made contact. Such damage is not uncommon, although it needs to be checked for nearby fractures. On the next maintenance cycle it should be filed smooth. This prop is flyable.


Junk going through the prop arc - sand, grit, dirt, gravel, bugs, etc - can cause much more serious damage.

On a pre-flight, this is one of the things I'm looking for and hope I never find. Along with more typical nicks and dings, there there is an actual "bite" taken out of the steel prop blade by a piece of gravel, with accompanying metal fracture.


The depth of that gouge alone, even without a visable fracture, would have me turn in the keys and drive home. The prop pictured above is no longer airworthy and is simply junk at this point. Attempting to fly with such damage can be lethal.

[Dalton]

I am reminded of Raiders of the Lost Ark...

[Broomstick]

Now that you've been educated, I'm going to quote from one of my recent flight adventures, as I think that in this context the full drama will come forward:

So I did, then hit the starter. The prop went around one and half turns and then backed up about 1/8.

Huh. "That's not right."

"No, it's not."

(We both have a talent for stating the obvious)

What most likely happened was that the battery was feeling the effects of the cold, had enough juice to get the prop around that time and a half, but not enough to get past the next compression cycle. When the battery stopped pushing, it was the compressed air in one of the cylinders pushing back that gave us that 1/8 of a circle reverse. It doesn't do that in summer because in summer enough turning to get just one cylinder through a compression-and-spark cycle is usually sufficient to start the engine, maybe two. As it gets colder the fuel gets less flammable, vaporizes more reluctantly, and the starter may need to crank much more than in warmer weather before the engine "catches" and starts running under its own power. With airplanes - as opposed to, say, your car - there is the additional complication that the batteries are small and the starter is expected to rotate a 35-40 lb/16-18 kg piece of steel.

"Hit the starter again." came the Voice From Behind Me.

We got half turn out of that one. I started doing the mental checklist thing, in the slightly frantic mental voice master, mags, mix, prime, throttle - did I just come out here for noth-?SHUT UP! - master, mags, mix...

"I suppose we get out and have a look?" I said, starting to unbuckle.

"You stay put, I'll get out."

"OK." I looked up at the electrical switches. "How about I turn this stuff off if you're going to be around the prop?"

"Good idea."

I reached up and flipped off the switches. J got out. I checked the switches. He asked me if they're off. I looked again, yep, off. He asked for some more prime, which I supplied. He grabbed the prop and pulled it around. The sound effects were different than normal. Louder and... well, sort of a clankity-grinding thing going on.

"J, does that thing have any oil on it?

"It's been awhile since it was flown, and with the cold..." Oh, yeah, in this weather the oil wants to turn to jelly. What was near the engine heater was warm enough, but out where the prop turns it was stiff. J pulled the prop around a couple more times, each time getting easier. He stepped back and looked down, shuffling his feet a little. Oh, I think I know where this is going... he's looking for good footing...

"Get on the brakes."

"Brakes on."

"You're sure?"

"Hard as I can."

"Give it some prime." he said. So I did. "Master on." >click< "Mags on." >click, click< I had my hand on the throttle and mix, watching J as he checked his footing one more time. J put one hand on a prop blade, pulled down and stepped back at the same time. The prop went rrrrrrRRRRRRR! just like it was supposed to do. J took a couple more steps away from it and circled around to get back into the airplane.

Just another routine day at the airport. Good pilots make it look easy and safe. And it IS safe - if you do everything exactly right, every time. Penalities for mistakes can be quite high.

When I first started flying someone told me something I've never forgotten: Always assume the prop is about to kill you. Because it really is that dangerous.

[Broomstick]

Didn't want to start a whole new thread for this, and it related to "prop dangers" even if not "handpropping dangers". This is from yet another accident. The horizontal lines were cut into the pavement by a prop:



Now, it may occur to you that props don't normally hit pavement. You are correct, they normally sit comfortably above the ground. This one was an exception. Why? Well, lets look at what's wrong with this airplane:



Someone forgot to put the landing gear down. And it really is that simple - they forgot to put down the gear. This may seem to be a mind-boggling omission, but it's been an occassional problem since retractable gear airplanes were invented. It doesn't matter how many lights, buzzers, and alarms you stuf into these machines, a couple times a year someone gets so busy and distracted on landing they forget to pull the lever. That's one reason I liked flying the Piper Arrow - if you drop below a certain speed it puts the gear down for you. That mechanism isn't perfect, either, and people have managed to land them gear up despite that, but it's probably prevented a few accidents.

No one got hurt, both occupants walked away unharmed. Damage to the airplane was significant, as you can imagine. You know how tires can give you black rubber skid marks? Below are shiny aluminum skid marks:

[tumbletom]

Wow that prop damage is bad....How often do you have to replace propellers (or do you only replace them when they are that screwed up?)

[BloodAngel]

As a student Aerospace Engineer, and hopeful pilot, this thread has proven to be quite enlightening... Many thanks.

[Broomstick]

Wow that prop damage is bad....How often do you have to replace propellers (or do you only replace them when they are that screwed up?)

Well, yeah, we replace 'em if they've obviously screwed up...

Not being an owner (I rent my airplanes) I've never had a reason to find out the expected lifetime of a well-treated propellor. They do last a long time, even wooden ones, provided they're cared for and nothing bad happens. I'm not sure if they have a mandatory retirement or not.

Propellors actually have log books that record all maintenance and official inspections performed, just as the engine and the airframe do. They're more than just simply an artfully twisted piece of metal - you need to consider the mechanisms achoring them to the engine, among other things. I usually fly fixed-pitch props, which are about as simple as they get. Constant-speed props, in which the angle at which the blades meet the air can be changed for greater efficiency in different modes of flight, contain moving parts and hydraulic systems, all of which require care and maintenance. Beyond that, there are props with anti-icing equipment installed, which is another layer of complication to deal with., reversing props, and in some motorgliders, even props that can fold away or retract into the fuselage.

Although most props these days are metal, they still make wooden ones and there are more and more composite models available.

[lukexcom]

Someone forgot to put the landing gear down. And it really is that simple - they forgot to put down the gear. This may seem to be a mind-boggling omission, but it's been an occassional problem since retractable gear airplanes were invented. It doesn't matter how many lights, buzzers, and alarms you stuf into these machines, a couple times a year someone gets so busy and distracted on landing they forget to pull the lever. That's one reason I liked flying the Piper Arrow - if you drop below a certain speed it puts the gear down for you. That mechanism isn't perfect, either, and people have managed to land them gear up despite that, but it's probably prevented a few accidents.

When I was going through my multi-engine training, we were on final for 31 at KSTC, a nice, big, long runway at 7,000 ft.

I was in the left seat of the BE-76 Duchess, my instructor in the right. The white landing gear knob was in the middle. Next to it were three green "Gear down and locked" lights in a triangular arrangement, with a red "in transit" light just above the lights.

Also, below the right-seat control yoke, was a panel of circuit breakers. Now, flight instructors tend to have a very irresistable urge to "play around" with these circuit breakers and look with amusement upon the student's reactions.

In my case, we were on final, with me having already pulled out and down on the landing gear handle. We got closer and closer to the runway, and all seemed fine. The airplane appeared to be performing predictably, and it seemed the amount of power I had *should* equal to the airspeed and performance that I was seeing. Now, remember, at that point, having only 5 hours logged in a multi-engine aircraft, I was woefully inexperienced with the nuances and the "small things" about that type of aircraft, especially considering that I was only 1/3rd of the way through the multi-engine training.

So everything looked good, and we ended up about 200 ft above the runway, a thousand feet from the threshold, when my instructor asks me, "So, does everything look good for landing?"

I instantly knew that something wasn't right, something that's a critical component for landing, something that I missed, because an instructor wouldn't usually ask that question of a pilot unless something was up. In a split second I quickly checked a few major things.

-Twin blue levers (next to the throttle levers) all the way up, indicating the propeller pitch full forward...check.
-Flaps down to 40 degrees...check.
-Gear handle down...check.

I didn't see the source of the problem, and the runway was getting ever closer, and I knew that a go-around would be occuring within the next few seconds. So I answered, "I don't see anything wrong. What did I miss?"

"Go around. You put the landing gear handle down, which is good, but you didn't look at the indicator lights."

After applying throttle to go around, and putting up the flaps, I glance at the lights. They are distinctly not shining green.

My instructor asked, "So what do you think is the problem? Burned out lights? Or is the gear really still up?"

I pressed on the top of of each light, which pushed it down a bit, and each light illuminated green. So the bulbs were good.

My instructor explained. "Your gear is still up, because I pulled the circuit breaker for it. The green lights are working, and they indicate that the gear is still up."

"How evil of you," I jokingly remarked. My instructor grinned, then explained, "Remember, a lot of gear-up landings are made because of inattentiveness. Always pay attention to all gauges, lights, and indicators. They're there for a reason."

"And as long as we're here, we can head out of the traffic pattern and practice some emergency gear extensions. And pretend there's nobody in the passenger seat to fly the plane while you do it." Yay. That meant me trying to keep the plane nice and steady (standard +/- 100ft. and +/- 10 kt. deviations maximum during this and other procedures, as perscribed in the Practical Test Standards booklets), while reaching in between my legs to try to twist the hydraulic release valve with a little tool on the floor between my legs, with my head at the level of my control yoke. Yes, we pilots ARE contortionists. Very precise contortionists, too.

But the lesson was well learned. The approach and landing phase has THE HIGHEST amount of workload for a flight crew. Exact attention, full awareness, workload control, and being able to fully implement the principles Crew Resource Management (CRM) are extremely crucial to sucessfully complete a flight day in and day out. And let it be known that this is not so easy to do every time. There are situations were the workload on a pilot approaches almost seemingly-ridiculous levels. The psychological stress at the highest workload points can be very burdensome, and has overwhelmed the occasional inexperienced pilot who was out of his/her element.

[MKSheppard]

Which is why on all my planes, an electric starter will be standard.

[Broomstick]

Yeah, that's a great idea Shep. Personally, I feel the same way.

Then there was that time I found myself 100 miles from home in the middle of farm country with an airplane I needed to get back to the airport and a passenger who was getting a little wild-eyed and an airplane - with standard electric starter - that refused to start due to alternator-battery failure. All of a sudden, hand-propping the little bastard Piper started to look like a good solution to multiple problems.

So, with a little assistance, that's what I did.

[Chardok]

Want to hear something funny? I can actually stand being on a prop plane better than a jet, dangerous as they are. Don't know why. Maybe I just think, like, since I can kinda see the moving parts, my mind thinks "If it breaks, I can fix it. I dunno...Anyhoo..Neat stories, Broom. If a bit...deathwish-y.


I would have killed my instructor where he sat had he done something like that to me, by the way.

I also would have consumed his young. To make sure that it never happens again.

[lukexcom]

Want to hear something funny? I can actually stand being on a prop plane better than a jet, dangerous as they are. Don't know why. Maybe I just think, like, since I can kinda see the moving parts, my mind thinks "If it breaks, I can fix it. I dunno...Anyhoo..Neat stories, Broom. If a bit...deathwish-y.

Heh, that quirk can be amended...

Did you ever hear of ASA Flight 529? A twin-engine, turboprop Embraer EMB-120RT. It's a sobering tale of cracked propeller blades and what happens when they fail.

Here's an excerpt from NTSB docket DCA95MA054...

Scheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Monday, August 21, 1995 in CARROLLTON, GA
Probable Cause Approval Date: 12/15/1997
Aircraft: Embraer EMB-120RT, registration: N256AS
Injuries: 8 Fatal, 13 Serious, 8 Minor.

Atlantic Southeast Airline Flight 529 was climbing through 18,000', when a blade from the left propeller separated. This resulted in distortion of the left engine nacelle, excessive drag, loss of wing lift, & reduced directional control. The degraded performance resulted in a forced landing. While landing, the airplane passed through trees, impacted the ground, & was further damaged by postimpact fire. An exam of the left propeller revealed the blade had failed due to a fatigue crack that originated from multiple corrosion pits in the taper bore surface of the blade spar. The crack had propagated toward the outside of the blade & around both sides of the taper bore. Due to 2 previous blade failures (separations), a borescope inspection procedure had been developed by Hamilton Standard to inspect returned blades (that had rejectable ultrasonic indications) for evidence of cracks, pits & corrosion. The accident blade was one of 490 rejected blades that had been sent to Hamilton Standard for further evaluation & possible repair. Maintenance technicians, who inspected the blade, lacked proper NDI familiarization training & specific equipment to identify the corrosion that resulted in fatigue.

The full Probable Causes document is available here

This is the result of a damaged blade by a fatigue crack from multiple corrosion pits. That, and various other contributing factors like "lack of required recurrent on-wing ultrasonic inspections" of the propellers, and so on.

A good book I have that goes through great depths on selected accidents is Aircraft Accident Analysis: Final Reports, James M. Walters and Robert L. Sumwalt. This one here

I would have killed my instructor where he sat had he done something like that to me, by the way.

I also would have consumed his young. To make sure that it never happens again.

As "sadistic" as it may seem to some, what my instructor did was done with very good reason.

The pulling of the landing gear circuit breaker simulates the faliure of the electrically-driven hydraulic pump. As it cannot release the hydraulic pressure, the gear stays up (on other planes, like the Cessna 182RG, hydraulic pressure is required to LOWER the gear, opposite of the system on this plane).

This teaches the new pilot to pay attention to the indicator lights and to be more aware of what is indicated in the cockpit. Had this been a real faliure of the hydraulic pump, and the instructor not there, then at that experience level I would have landed with the landing gear up.

But because the flight instructor is there, and he pulled the circuit breaker, he is aware that the landing gear is up. He will NOT allow the plane to land in this condition, whether letting the student arrive at that conclusion by himself, or if that fails, then by letting the student know that something is up, or if even that fails, then by taking command of the plane and going around.

Yes, I said that flight instructors tend to enjoy doing this, and like to observe the students' reactions. But the reason why this is done is because it is a very effective learning tool, a safe way to simulate a faliure in-flight, and is used everywhere. Said amusement is a side benefit for the instructors.


I don't know if I mentioned this in the past, but multi-engine training involves you flying the aircraft, and then suddenly the instructor simulates a faliure of one of the engines. By reducing the throttle to idle, effectively leaving you with one engine. This typically happens once or twice per lesson. It is to permanently ingrain the procedures and motions for engine faliure into your brain as effectively as possible, almost making it a reflexive action.

The most interesting engine-faliure simulations are the ones where your flight instructor completely shuts down the fuel flow into the engine. Naturally, this makes the big spinning prop thingy stop spinning....completely. The engine is shut down in flight, and you then perform an engine restart, whether by windmilling the prop (gain enough airspeed for the wind to "hand-prop" the propeller), or by using the electric starter, as appropriate to the situation at hand.

The one annoyance is the sheer leg-power required to depress the opposite rudder pedal to the failed engine, so the airplane keeps flying straight (because of asymmetrical thrust from the remaining good engine). You work up a sweat quickly as you jam your leg into the rudder pedal as hard as you can.

[Julhelm]

This reminds me of the flight deck footage from "The Fighting Lady" where the mechanics casually go about their business around that menagerie of rotating meatmills.

[Broomstick]

I would have killed my instructor where he sat had he done something like that to me, by the way.

I also would have consumed his young. To make sure that it never happens again.

As "sadistic" as it may seem to some, what my instructor did was done with very good reason.

I agree... in flight training you think your instructors are sadistic, evil bastards. Until you have REAL emergency and it's just your lone ass on the hotseat who has to save the day, and you realize that Mother Nature's middle name is "Fucker".

After you survive the experience, you go back to that evil, sadistic bastard, genufluct a dozen times "we're not worthy!", and offer to kiss any body part he chooses in gratitude for pounding those emergency procedures into your thick skull.

Then he breathes a sigh of relief that your heirs do not yet have an excuse to sue him

[Broomstick]

Here's another accident. A gent was fueling his Piper Cherokee at a self-serve pump. For some reason, he couldn't get it to start in the normal manner. So he took it into his head to handprop it. No big deal, right? Its shouldn't have been. However, not only did he start it with the throttle at 3/4 open (you really only need to be just above idle) he also failed to either put the parking brake on (which in this model is actually pretty decent) or to chock the wheels. Well, he got it started alright, and somehow managed to get out of the way himself. The airplane "made contact", as they say in the accident reports, with the steel and concrete barriers around the fuel pump. Which stopped the airplane and spared the pumps. It also nearly stopped the prop. When an irrestiable force (the prop) meets an immovable object (concrete barrier) something just has to give. In this case, it was the crankshaft:



Wait a minute, you say - I don't see a prop! Well, not on the airplane, anyway. Here's the route the prop, spinner, and part of the engine took after departing the airplane:



And here's the roving bit itself - it's in pretty good shape, all things considered. I mean, it's still recognizable as a prop:



Today's safety tip: If you see someone handpropping an airplane, stand behind the aircraft where it's relatively safe.