It was SOP on Britannias as I recall it. When I were but a lad my crew used to service the CP Brits transiting SYD and that was one of my jobs, hold the prop until it pulled away from my hands in the correct direction of rotation.

Always had quite an audience!! :ok:

Once again, as we dinosaurs know well, this is fine just so long as you know that turning a prop through a compression can cause a hot engine to fire with the mags switched off.

I shudder when I see students assiduously doing their pre-flight and grabbing the prop to give it a turn on an aircraft that was landed and vacated 15 minutes before by the previous user, and I look away when I see people grabbing a hot prop to move an aircraft that landed 5 minutes before. Trust me; it happens.

It's Darwin Award territory.

My passenger briefing includes "Stay away from props, especially ones that aren't going round. It only takes three things to go wrong at once for a prop to burst spontaneously into life, and we like better odds than that around little aeroplanes. So, no selfies draped across the prop please."

On holding props during compressor washes http://www.pprune.org/accidents-clos...ml#post9100126

This was standard practice on PT6's As a free turbine engine its easy at motoring speed. Don't try it with a TPE-331 though.

Props and chocs
 

We were doing engine runs on a rebuilt Stamp SV4 fitted with the Renault engine. This had an air starter with a little knob on the panel that you pulled out. This in turn had a little spring loaded lock, so both hands were required to operate it.
One of our junior mechs was in the seat and got ready to start, while I put the chocks in front of the wheels. With not much pressure in the cylinder, the knob needed to be pulled out over an inch before anything happened, but I had been running the engine just before, so the cylinder was fully charged. As soon as he moved the knob the engine turned, and fired, as he had the switches on.....The blade went through the hair on the back of my head (had more then..) Choice words followed about not taking anything for granted, and sticking to the rules.
DW

When I was a mechanic we would do engine runs in the middle of the night on beater Cessnas, huge torch in hand, checking for oil leaks after maintenance. I would ALWAYS have one hand on a strut, and if I couldn't see the front of the engine using that method then so be it. The scarest part was adjusting the carb idle screw while that puppy was running.

One time at a remote airfield I had a dead battery in a Cessna 150. I was deciding how I would hand prop it without anybody around to hold brakes when an old grizzled IA drives up out of nowhere and offered to help. He told me to get inside and hold the brakes while he tried to hand prop it. After a while he was unsuccessful, so he pulled up his car and jumped the battery.

But in order to get the battery box lid back on, this old grizzled IA withstood the mighty wind forces the O-200 was producing and stuck his hands in the tiny access panel to pin it in. The angle was screwy, so he was gyrating all over to get it in, bringing parts of his body within inches of the blade. I was holding the brakes like mad. He eventually was successful, gave me a slight nod, jumped in his car and drove away, leaving me alone with the weeds and coyotes to contemplate life.

compressor wash
 

Thruster763 obviously paid no attention to maintenance manuals. Cowboy attitude. MM specfically states not to hold prop during compressor wash on PT6. On 331, no advantage derived from compressor wash.

I was told when I started on museum aircraft that there was a problem with the Wright powered aircraft, where if a relay stuck on, with GPU applied the starter would turn and as a result the prop would turn.

One day I powered up our Neptune and as the plug went in, the starter engaged. Fortunately on the L/H side where the GPU plug is,so it was obvious immediately.

The other Wright aircraft in our fleet needed power to be selected on the F/Es panel but it was possible with that as well. It took me quite a bit of arguing to convince the others on site that this was a real threat.

Wunwing

When I was at Seletar in the 60s we had a squadron of Beverleys. The prop clearance on this aircraft was about 7 feet and although it was forbidden some of the blokes used to take a short cut under the props. This was ok until one of them got a posting across to the Argosy squadron at Changi and tried the same trick there, with predictable fatal results.

I stopped someone walking into a prop.
Arriving a Britannia, I was on the headset as chock man installed the nose chocks, then proceeded towards the MLG to put the chocks. Only problem was that spinning prop was between him and MLG. He was head down with ear muffs on, dragging the chocks on ropes.
He didn't hear my shouting - I managed to rugby tackle him just ahead of the prop.
Far as I remember (it was 40 years ago) he just cursed me for hurting his knee.

Indeed, I remember that. The Brit did not like to start with the prop reverse rotating, so we needed to hold it during start. We had competitions to see who could hold the longest! Silly really, I wonder how we survived it.

A further point about the dangers of a live prop.

After shutting down our gliding club's C-182, we always put the keys on top of the glare shield so that someone outside can see them.

However, that is not a guarantee that the engine can't start. Apart from the obvious issue of a potentially broken ground wire, it is also possible with some keys, to remove them from the ignition switch, when it is set to Both.

I have personally had that happen to me with a PA-28 and I've heard that it is fairly common.

How to get onto a floatplane when parked nose in to a jetty: hold on to the propeller as you step onto the front of the float (there's nothing else you can reach). Never entirely happy with that sort of thing.

1. Always treat the propeller as being live

2. Never touch a propeller unless you have too

3. pass the message on ... !

I seem to remember a loader was killed at Aldergrove in the mid 90s when he walked into a HS748 prop?

When I was training we were instructed to walk out to the A/C and perform our pre-flight checks and then start the engine and waiting for the instructor to board before calling for taxy. It used to worry me everytime when I watched the instructor climb onto the wing of the HR200 and then open the canopy and climb in. It’s so easy to slip and fall over the leading edge and within the prop arc and I’m surprised an issue hadn’t already pccured to that day.


Eventually (still as a student and after) I decided to simply wait for the instructor before powering up off my own occurred.

Drummed into me while I was in the CCF by a serving RAF officer several decades ago.

A couple of decades later I was watching the Italian AF giving a demonstration of mountain rescue at a ski resort, using a large helicopter. It was sitting at the bottom of the pistes rotors running, when for some reason the co-pilot got out and walked round the back. He slipped on the snow and fell into the tail rotor. 2 stretcher bearers ran over from a parked ambulance: when they reached the scene they just stopped running.
A couple of hours later, having tidied everything up, the helicopter started up and flew away. Without any sort of inspection.

On another thread. A cautionary tale from Dunnunda.

Please DO NOT put all your faith in the Mag Switches being OFF.

Decades ago I spent many years as ground crew in the RAF on all sorts of propellor aircraft.
One of the tasks each morning was to turn the engines over using the prop to check for oil leaking into the cylinders (if it did the resulting hydraulic effect on startup could blow the cylinder head off).
We clearly always checked that the Mag Switches were OFF, but still had a fair few engines burst into life in the hanger........certainly catches your attention!

The cause was faulty Mag Switches or associated wiring.

Magneto switch circuitry is different to most other electrical stuff in that the electrical circuit has to be in perfect condition and the switches closed (ie technically "ON") in order to disable the Magneto.

SO IT IS NOT FAIL SAFE - if anything is broken or damaged THE MAG IS ON.

.............Never walk through the arc of a propellor, let alone touch it.

If you do have to turn a prop over, always assume its going to fire and move away from its arc.

If this happens then the mag switch is US and the aircraft must be grounded until it is fixed. All of the standard light airplane mag switches are specifically designed so that you can only remove the key when the switch is in the off position.

I check for this at the end of every flight by giving the key a little tug at each mag position as I cycle it to off. I have found a few bad switches over the years, all in high time trainers where the switch is just worn out. My guess is in all cases the switches had been like that for awhile but nobody had paid any attention to what they were doing when they shut down :ugh:

When a student on No 16 Vampire/Varsity course at Oakington in the 60's I was told about the "civvy" who, in WW2 and before first light, cycled to work round the perimeter track.

They were equipped with Stirling bombers with their extended undercarriage legs that ensured the four engines had plenty of clearance under them. Knowing this he would remain on the taxyway rather than take to the grass to pass them.

Sadly they re-equipped almost overnight with Halifaxes and he still took his usual short cut..... but through the props rather than under them.

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.

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
Dumb-a**
Kevin

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.

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

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:

SB-912-036
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.”

and

SI-04-1997
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.”

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.

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.

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!

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

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.

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.

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.

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?"

http://performancepowerracing.com/wp...10/74g9759.jpg

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.

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


https://assets.publishing.service.go...BNSZ_08-17.pdf

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.

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,

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.

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