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-   -   Safety around propellers (https://www.pprune.org/accidents-close-calls/562596-safety-around-propellers.html)

NutLoose 5th Jan 2017 23:25

I always turn props backwards as it reduces the chance of it firing due to the impulse coupling not engaging on those that have it installed.

As for what was said re mag switches, I had one even worse than that, the starter solenoid on one had jammed in and simply turning the battery switch on resultied in the starter turning the prop over.

Flyingmac 7th Jan 2017 10:57

I always turn props backwards
Presumably you listen carefully for the 'Tink' sound of a breaking vane on a dry vacuum pump?

From another forum.

I know better, being a mechanic and all. I park my little Porsche 914 in front of the wing of the Comanche. To get the best clearance I swing the prop vertical so I can back in or pull out with ease. Well, the last time it was just a little off and i pushed it backwards and thought I heard a little "tink".https://www.pilotsofamerica.com/comm...smilies/no.gif Didn't think much of it until I flew down to Eugene, Or. and noticed the vacuum gauge needle flickering a bit. Upon the return trip no vacuum at all. Needless to say the Comanche has a new vacuum pump on it now... Oh and the one inner lower nut, washer and lockwasher was a real pain in the butt too.https://www.pilotsofamerica.com/comm...milies/yes.gif

stevef 7th Jan 2017 14:31

I've posted this before a couple of times - turning the prop backwards does NOT damage the vacuum pump. This is from Parker Hannefin, who manufacture them. I've lost the email the service department sent to me years ago confirming this but everyone's free to send their own enquiry. :-)
Anyway, turning the prop backwards is part of the magneto timing procedure and I've never heard of anyone breaking the vanes by doing that.
The pump killer is oil, solvents or water.

India Four Two 8th Jan 2017 07:37

On the 182 that I fly, you can't turn the prop backwards, due to the construction of the starter adapter.

Forfoxake 20th Mar 2017 11:24

Turning the prop backwards (over one or more revolutions) on Rotax 912/914 engines can apparently cause ingestion of air into the valve train and require a venting check:

Service Bulletin: Inspection for correct venting of the oil system for Rotax engine type 912 and 914 (series)
SB-912-036 R1 SB-914-022 R1
Cited in Compliance 1.5 – “engines which have had the prop spun for more than 1 turn in reverse direction allowing air to be ingested into the valve train.”


Service instruction: Venting of lubrication system for Rotax engine type 912 and 914 (series) SI-04-1997 R3
Cited in 1.3 Reason – “and/or had the prop spun in the reverse direction allowing air to be ingested into the valve train.”

tonytales 25th Jun 2017 05:34

Even though well indoctrinated in avoiding prop arcs I nearly walked into one. Midnight shift of course, only three mechanics on duty and we had to adjust the hydraulic pressure for the autopilot of a DC-4. The regulator was located in the hydraulic hell hole accessible through a hatch on the starboard side at about the wind leading edge. No pressure gauge down there and no aux hydraulic pump on the ex C-54 so you had to run an inboard engine for pressure. So, one of us in the cockpit to run the engine, ride brakes and observe pressure, one in the hydraulic hell hole to adjust the regulator and one in the cabin above the hydraulic hell hole to stamp on the floor. That was to signal me, the guy in the hell hole to raise or lower the pressure. No maintenance intercoms on this old bird, no hearing protection either in those pre-jet day (1954).
So I stood fire guard wile #3 engine was started and then carefully made my way clear of the props around behind the RMLG and up the short ladder and into the hell hole.
The R2000 engine was not the only source of noise. Being in and among the hydraulic system lines and valves, they were singing loudly too. Screeching was maybe a better word.
Lots of stamping and banging as I adjusted the regulator but it turned out to be faulty, probably worn internally. It would overshoot either up or down but would not settle on the desired 600 PSI (I seem to remember) no matter how carefully I tried to set it. After an eternity we gave up, lots of stomping. Half befuddled by engine noise and hydraulic screeching and midnight shift lack of sleep I backed out of the hell hole, down the steps, turned right, took a couple of steps forward and realized there was a prop whistling by a foot in front of me. My knees almost gave way.
I have been a fanatic on prop safety ever since but, yet, I too am one of those who held the prop whilst a Proteus tried to start up in a tailwind.

IcePaq 2nd Jul 2017 01:22

Turning a prop backwards causes the oil to reverse direction and air to enter.

Depending on where it ingests the air is what determines the severity of the problem that may arise at next start.

I parked a car on a hill and put the manual transmission in a forward gear.

When I came back out, it had moved down the slope about 15 feet.

That was enough to slowly draw the oil out of all the hydraulic lifters and tensioners and the engine almost threw the chain off and the lifters clicked for about 10 minutes afterward.

Russell Gulch 2nd Jul 2017 22:09

Originally Posted by IcePaq (Post 9818557)
Turning a prop backwards causes the oil to reverse direction and air to enter.

Depending on where it ingests the air is what determines the severity of the problem that may arise at next start.

I parked a car on a hill and put the manual transmission in a forward gear.

When I came back out, it had moved down the slope about 15 feet.

That was enough to slowly draw the oil out of all the hydraulic lifters and tensioners and the engine almost threw the chain off and the lifters clicked for about 10 minutes afterward.

What bollocks.

DANbudgieman 4th Jul 2017 05:27

During the very early eighties nose in parking of aircraft on stand became obligatory at Glasgow airport.

The powers that be decided in their infinite wisdom that it was possible and desirable to use an air bridge in conjunction with the twice daily British Midland Viscount service to East Midland.

The procedure agreed with the BAA was that a heavy duty wooden (nose wheel)chock was installed at gate 17. Used in conjunction with AGNIS light this was intended to ensure that the aircraft would safely be brought to a halt in the required position before contact between the props and the airbridge became "an issue."

This system worked well enough and the dear old Viscounts were eventually replaced by DC9s. The introduction of the DC9 with the removal of the props in near proximity made for a much happier experience for all concerned on the ramp!

How this system came to be regarded as acceptable to both the airport authorities, the Viscount aircrew and the ramp crew god alone knows!

IcePaq 7th Jul 2017 05:32

Originally Posted by Russell Gulch (Post 9819196)
What bollocks.

You obviously don't understand how internal combustion engine lubrication systems work.

Consol 7th Jul 2017 06:10

Having done some flying in the good ol' USA where you are encouraged to yell 'Clear Prop!' (I'm softly spoken so no one ever hears), I found myself back home at my local airfield. About to start my engine I observed an instructor and student at another aircraft parked alongside. I earnestly called 'Clear Prop!', no one heard. I signalled engine starting with hand signals several times to a now bemused looking pair. Then the instructor walked over to my aircraft through the prop arc, put his arm over the front cowl and helpfully asked if everything was alright!
Never earnestly assume that everybody else knows about hand signals and prop safety.

rnzoli 7th Jul 2017 09:00

Originally Posted by Consol (Post 9823143)
where you are encouraged to yell 'Clear Prop!' (I'm softly spoken so no one ever hears).

I always open the DV window and literally scream "Clear prop!" to the outside world, because in small airfields, dogs or even small children can easliy approach the lower part of the prop arc without me seeing them.

And then there was one time, when I forgot to turn off the intercom before shouting, and made myself and my passenger deaf for the next 2 minutes.

mustafagander 7th Jul 2017 10:40

IcePaq, I would love to read your explanation for these assertions. I fully agree with Russ G, utter bollox. Please enlighten us, me especially. If you're right I may have wasted a lifetime as a mechanical engineer by not knowing this stuff. I need science, not anecdotes or assertions mate, I've been in the game over 50 years.

IcePaq 7th Jul 2017 17:44

How hard is it to understand that turning an oil pump backwards will draw the oil out of the engine through the pump and to the oil pump pickup/sump?

When an engine is sitting you have gravity working on the oil but, you have to have a path for it to move down and out of the engine.

That path is measured in the thousandths of an inch of whatever clearance you have in your positive displacement oil pump.

The flow rate is so low that I routinely start cars that have been sitting for 4 years and only the valves that were open had lifters bled down meaning only two valves clicking until oil can pump the lifters back up and remove the clearance.

Unlike leaving a car sitting for a long period and possibly having oil drainback, turning the engine backwards uses suction to draw the oil out of where it would normally not leave.

So a car placed in a forward gear on a hill with Ebrake not properly applied will slowly roll down the hill depending on how steep it is and what gear the car is in.

I made the mistake of 3rd gear instead of 1st or reverse so the car rolled about 1.5 lengths down in an hour before I came back.

In my case, I had all lifters clacking as if they had zero oil in them for a period you might see when running a new engine for the first time.

Remember that the oil leaving these devices end up being pushed around a bearing or the tip of a lifter in normal operation so............turning the engine backwards now makes any "oil exit" a perfect "entrance" for air to enter.

I have already witnessed it as described above and the physics is quite basic.

Turned backwards at the right speed, you can generate quite a few inches of vacuum (mercury) which will pull oil from wherever it is until one route of air entry empties and increases in flow rate causing the rest of the entry points to nearly stop..

That short amount of time is more than enough for oil to be sucked from the lifters since it only has to travel about 5/16 inch before the lifters are empty.

I do turn engines backward but only to "prime" the oil pump when it is impossible to do it with a tool and then only on engines that don't have a device that would be damaged by reverse rotation or may skip a belt tooth since the tensioner is not pumped up yet..

I hook a clear plastic hose to a long and skinny funnel and run it to the port that supplies the oil filter boss.

This port goes directly to the oil pump.

I fill the funnel with oil and turn the engine backwards and watch as the oil is quickly sucked down through the tube and into the port which leads to the oil pump.

I pump at least a quart to ensure the oil has gone all the way down to the oil pickup.

Now I know that the oil pump is full, and that the gallery leading away from it has a nice column as well so I fill up the filter as much as possible and crank the engine.

It's the same mechanism as what empties an engine except I am using it for the opposite by supplying oil from where the reverse rotated engine would seek air.

I get oil pressure immediately at the pressure sender port so I screw it in and undo the oil supply line to the turbo and crank until it comes out there.

Then I enable ignition/injection and start the engine.

Is it possible that your lifetime as a mechanical engineer never brought you to this exact condition.

I've got plenty of gaps in my mechanical engineering knowledge but my engine knowledge has me working directly in this area my entire lifetime.

Ask me about other things and you may find a hole............but not here.

If you think my answer was harsh, it's simply tit for tat replying to a BS post of "pure bullocks" which had zero scientific merit.

I'm the guy on the right asking "why did you guys run 30 pounds of boost to it without filling the methanol tank?"


tescoapp 9th Jul 2017 06:29

Well as another engineering type I would say its completely dependant on the engine design and component design about what's going to happen.

For some it won't be a problem and others its going to break something.

BTW the ability of vacuum pumps to be turned the opposite way only really holds with new ones. Mid life units which have only been run one way your asking for trouble mainly due to wear profiles and material properties changing. Normally you will get gradual wear but one turn in the wrong direction and you "might" get bigish lumps coming off instead of the normal dust wear erosion.

As for the aero engines what may be ok in a normal utility engine with no inverted capability might do some quite nasty damage to an engine with inverted flight certification. Aero engines will have none return valves where as car engines won't in various systems. So I do actually agree with everything Icepaq says about consumer car engines.

But for me it is quiet dangerous to the wallet to presume that they translate directly to aero engines. All it takes is one none return valve to operate as per design and you have issues. Gravity time flow isn't an issue, but as soon as you get about the valve operation threshold then your into outside design operation.

cyclic35 10th Aug 2017 11:40

A very close call. :rolleyes:
Always assume the prop is "Live".


Fostex 11th Aug 2017 08:15

That PA28 isn't that bad, in the same Aug 17 AAIB report is the G-MYUB where the flexwing guy put his head into the prop and amazingly survived!

G-MYUB was an incident which occured during a ground run in which the injured party was doing checks rather than intending to go flying. Easy to drop your guard when perception of risk drops.

Homsap 21st Oct 2017 11:36

If someone disembarks or boards on a Cessna the door and wing strut generally prevents someone walking into a live prop. like wise on Pipers the door again prevents someone walking into the prop.

The problem is with aircraft with sliding canopies such as the Bulldog, Grob115, Robin DR200, DR400, the poblem is boarding with the engine running, that you could slip on the wing and fall of the front of the wing, likewise upon disembarking an aircraft the danger is 'going the wrong way' and jumping of the leading edge into the propellor. I was warned of this when I started flying DR200s, as I was told this happened with fatal results at Sywell in the eventies and eighties.

During my career on several occasions I have seen people hand swinging aircraft, when there is no occupant in the aircaft, utter maddness!

Historically, the RAF did live changeover of air cadets on on the DHC Chipmunks as the had explosive cartriges and their were only six, but the air cadet was always ecort. It would be interesting to know what happens on the RAF grob? In the instructing world instructors have in the past asked student pilots to start the engine and then board.

As most modern aircraft have electric starters, there is no need for anyone to board or disembark with a live engine. On aircraft where handswing takes, the person who is handswinging and the occupant should be sufficiently qualified, trained and pre=briefed not to walk into the prop,

Chuck Glider 22nd Oct 2017 08:41

Originally Posted by Homsap (Post 9932038)
...I have seen people hand swinging aircraft, when there is no occupant in the aircaft, utter maddness!

Other opinions are available. I do it all the time. It's even shown in the flight manual for my aircraft.

[edited to add]
Generally solo hand propping is done from behind the prop with the controls within reach.
It's still not a place to be careless in your movements but with reasonable care and attention it is quite safe.

tmmorris 22nd Oct 2017 13:28

Originally Posted by Homsap (Post 9932038)
It would be interesting to know what happens on the RAF grob?

Engine is stopped for cadet changeover AND the cadet is helped into the aircraft by ground crew.

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