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  1. #1
    Co-Pilot D-Flyer's Avatar
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    Forced landing - order of switching off

    Hi all

    I'd be interested in opinions here, and this is purely hypothetical - lets say you're forced to land out in a field, either after a semi-engine failure or as a precautionary. On lining up, you notice the field you've picked is a little rough, so this might not be a smooth roll out and you could end up upside down.

    If the engine is still turning over of sorts, and it's time to go through and switch off fuel and mags, my question is this - if you know you'll definitely make it in, is it worth considering switching the fuel off first and letting the remainder get burnt so there's nothing in the pipes and carb bowls before mags go off (I think I've heard somewhere that's about 30 seconds on a 912), or would you think that the limited amount of fuel in the pipes / carb bowls etc isn't a big risk? Would you gamble on 30+ seconds of glide rather than stick with a semi rotating engine? And is there a benefit in not having the prop rotating in such a scenario, either for lessening flying debris on a possible nose over, or to prevent shock load on the motor?

    Your thoughts, as ever, are welcome!

    D Flyer
    <Insert wit here>


  2. #2
    Co-Pilot Peter Twissell's Avatar
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    I very much doubt that the engine will burn any of the fuel in the pipes. It will run until the level in the float bowls is low enough to weaken the mixture significantly.
    More important is that the fuel tap is off, so fuel is not free to flow from the tank in the event of damage to the pipes, filter etc.
    If the engine is so sick that the decision has been made to make a forced landing, then I'm not sure what might be the benefit of keeping it running at all.
    I would expect to attempt to restart the engine, or improve it's running by such means as possible (manipulation of throttle, choke and ignition) until committed to the landing (say 200 ft altitude) and then switch off everything.
    G-BZNP Still not dead


  3. #3
    Co-Pilot Martin Watson's Avatar
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    Peter is absolutely correct in that switching off when you are ready is much better than leaving the engine running to stop when it wants to. The latter just makes it harder for you to judge the approach.
    Keep it simple and make life easy for yourself - much the best way.
    More generally, it's a good point to raise - we don't really train for a partial engine failure, though they are not uncommon. The trouble is that you never know how long the engine will run delivering partial power. Much the best plan is to switch off and then fly it as a full failure because that's what you are used to.
    Martin
    BMAA 5370


  4. #4
    Co-Pilot Peter Twissell's Avatar
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    Russ, I have to disagree. Fuel can only flow to the engine if air can get into the pipes to replace it. If the cap breather becomes blocked on a motorcycle fuel tank, after a few minutes the engine will stop through fuel starvation, although all the fuel is above the engine and the tap open. The partial vacuum created in the tank (about 25mBar for a 300mm height) will prevent fuel from flowing.
    G-BZNP Still not dead


  5. #5
    F-UK FLYER
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    D-Flyer,
    There are 2 trails of thought in my mind ( or I should say 2 different scenarios ).
    (1) If the prop is creating a modicum of thrust I would keep it running for as long as possible ( partial failure with no vibration scenario )
    (2) If the prop isn't creating a modicum of thrust, it is acting as an air brake !!!!! Shut it down ASAP and become a glider.

    In (1) Shut fuel off when you know you will make the field....then mags off.... Ignition switch off ( if fitted )
    In (2) Shut everything off immediately. ( The order isn't important )

    Bob Hoover ( Aviation Legend ) said :
    quote-if-you-re-faced-with-a-forced-landing-fly-the-thing-as-far-into-the-crash-as-possible-bob-.jpg


  6. #6
    Co-Pilot Peter Twissell's Avatar
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    Russ - The fuel pumps can only generate a limited vacuum. When that vacuum is reached in the fuel pipe between the tap and the pump, no more fuel will flow. Since there is (or should be) little or no air in the fuel pipe, the displacement of fuel necessary to generate vacuum is small.
    I used the motorcycle as an example to illustrate the point, because it is something many of us are familiar with.
    G-BZNP Still not dead


  7. #7
    F-UK FLYER
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    Quote Originally Posted by Russ_H View Post
    "Much the best plan is to switch off and then fly it as a full failure"

    I agree, though every situation is different and PK's comment about the degree of thrust available would effect my decision, you don't want to be dealing with an erratic engine on final, though if you have some available thrust and still at a fair height it would make sense to use it to position to a good field and then switch off when certain of making it.

    That's my take anyway, but of course, easy to say sat here in front of a PC
    Taking a part of Martin Watson's post as a 'counter' to my previous comment
    Quote Originally Posted by Martin
    "The trouble is that you never know how long the engine will run delivering partial power."
    From previous experiences I have always chosen to keep the engine running if there is partial power on the assumption of thrust being present ( I think we all know what RPM creates thrust & what RPM creates no thrust so that would be a defining factor in 'KEEP RUNNING' or SHUTDOWN in the engine we have fitted.
    Quote Originally Posted by Martin
    Much the best plan is to switch off and then fly it as a full failure because that's what you are used to.
    I am not sure opting to accept a full failure is what everyone is used to? I have practiced forced landings continuously & practicing with a modicum of idle power gives a different result to having a full shutdown.
    The practice mode gives you a fighting chance of getting it right when the fan fully stops. I have only ever suffered a full shutdown once & I will openly admit that the chosen landing point was 200m too far away, luckily I was over a large estate with a lot of lush grass and whilst aiming at my keypoint I quickly realised I would be arriving short ( not a biggie in that situation ) but if my keypoint had been the only viable landing spot I would have been arriving at a less suitable place. You only need to look at Realtime forced landings and quite a few go awry..... You can only give it your best shot in every instance.


  8. #8
    Trainee Pilot newflyer17's Avatar
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    Does anybody actually switch the engine off to practice forced landings, then fire up once nearly down.
    Or is that simply far too risky in case it won't start again?


  9. #9
    Training Captain Gentreau's Avatar
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    Quote Originally Posted by newflyer17 View Post
    Does anybody actually switch the engine off to practice forced landings, then fire up once nearly down.
    Or is that simply far too risky in case it won't start again?
    Yes, I do it all the time. The difference in glide between idle and engine off is significant.
    It's also good to experience the silence and get used to listening to the wind noise when you're at the right glide speed.

    However I have a strict procedure.
    1000ft overhead, throttle to idle, mags off.
    When the prop stops, mags on, ignition off then on (to ensure starter fires first time)
    Decision height 200ft AGL. If the runway is made, continue, if not restart and go around, no hesitation.
    Never had a problem restarting the 912S on the club machine.
    The three most useless things in aviation:
    • The air above you.
    • The runway behind you.
    • The fuel in the bowser.


    Rule #1: Always tie your aircraft to the largest heaviest object available. The planet Earth meets these requirements and is readily available in all locations.
    Rule #2: The great thing about twin engined aircraft is, if one engine fails, the other engine always has just enough power to get you to the scene of the crash.

    Semper specto in clara parte vitae.

    .


  10. #10
    Co-Pilot sssdu01's Avatar
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    I am not an instructor or any more qualified than anyone else, but this is what I practice for

    If I think the engine is on fire then

    1 shut down fuel i.e tap off, pump off if its electric.
    2 open throttle to burn off as much fuel as I can
    3 Engine will then stop and you are into a deadstick situation so now get your mayday call in etc.

    Partial power

    1 I would always assume the engine is going to stop in a few seconds.
    2 If you have height then you have options so mayday call, and have a fiddle with throttle/choke/fuel taps/electric pump etc (but dont fiddle with mag switches as if running badly on one good mag it may not restart)
    3 Fly back to your nearest airstrip with whatever power you have but keep a lookout for the "best field" to land in if the engine dies
    4 Set your own minimum height limit (depending on where you are flying an what type of plane you have) e.g if I was flying over flat farmland my chicken out height would be 1000 feet ie once I got this low under partial power then I would decide to pick a field and land. If it was a forest I would want to be in glide distance of a suitable field at all times and my chicken out height would probably be 2000 feet
    5 Once I get to me chicken out height then pick the longest looking field into wind and set yourself up for a landing and I would get close to "final" and throttle back and then turn off the fuel tap once I am sure I can make it into the field i.e I am not landing sort

    If the engine dies you are into deastick scenarios

    1 Turn off fuel tap/Pump.
    2 Put in mayday call
    3 Pick most suitable landing field into wind
    4 Pick one that might be closer as you cant extend with no power
    5 Keep up airspeed
    6 Dont pull back on stick if you think you are landing short as you will land even shorter or stall
    7 if you have time make sure your straps are as tight as you can get them
    8 Learn to side slip as this will help you to loose height if you are landing long (do this with an instructor)
    9 If you have a non pilot passenger tell them whats going on and that you have done this loads of times

    There will of course be variations on this e.g if you were flying over uneven rocky ground or water etc then you might use a tail wind to get you to a safer position and then plan out what you are going to do.
    Above all if you have any doubt talk it through with your instructor and practice flying with no engine


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