GTSIO-520 Starting techniques

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    When I was doing my transition training in the 421 I was taught to start it like any other engine, mixture prop throttle forward, prime, throttle back to 1″ open and apply the starter. I’ve never had any problems starting like this but I know the manual cautions against hydraulically locking the cylinders. I later noticed the procedure in the manual (it helps to read it some times) which involves mixture & props forward then hit the starter and prime at the same time until the engine starts, which I’ve used lately and it seems to work fine.

    Using the manual’s technique seems to require the starter to be active longer and I’m wondering if that is harder on the starter than when priming first. To be honest I have not timed the starts to see if there is any difference.

    So the question is how is the group starting 421s?


      I give the primer a 2-3 second head start, then engage the starter and hold both until it starts. Try not to allow the engine to exceed 800 RPM on the start.

      The same thing when it’s warm. If it doesn’t start after 5 seconds, release the primer and go to full throttle until it fires.

      This procedure has worked every time for the last 36 years I have operated 520’s.

      Enjoy your airplane.



      I find it is best to have at least two different techniques. when the first one fails on the left engine, you can try the second on the right… 🙂

      I believe some 421C’s have an additional prime circuit when the mixture is full rich (just when the prime is pushed). I press prime for a couple of seconds then hold it while cranking with the mixture full rich, and throttle cracked a bit.

      works well at most temps. When it is warmer, prime less, when it is really warm – maybe no prime. If you flood it, prime off, throttle full and then pull the throttle back when it catches

      When it is cold, usually I end up priming way more than I think it needs but eventually it catches. Pre-heating is an even better way of avoiding a cold start.


        I used Pat’s technique – giving the primer a few seconds head start.


        Thanks Guys, Ill give that a try and see how it works. I’m also going to try to time the starts to see if there is any real effect on how long the starter needs to engage.


        I am in the same boat as everyone else during normal starts and hot starts.

        Normal starts (first flight of the day) I prime until FF peaks (usually 2-3 seconds and 10-12 gph) and hit the starter. Starts within a blade or two on each engine.

        Hot starts (if flown within an hour or so) – no prime and straight to starter. I have to be on the ball when the engine fires with the boost pumps to low. Usually within 2-3 blades.

        Cold starts….I have fits with these. I try and pre-heat whenever possible, but the other day I started when it was about 50 degrees outside, and then again when it was about 20 or so and the airplane was sitting on the ramp for 3-4 hours after a long flight. I had fits with my normal procedure and it took a LOT of coaxing before I could get the right engine to fire off. I know now to pre-heat and/or blanket the engines like this, but does anyone else have any suggestions for cold starting? Is it easy to flood the engine and then I guess I need to revert to full throttle until she fires? I am extremely anal retentive about keeping the RPMs low on start up.

        I would love to hear everyone else’s thoughts on cold weather starts on these beasts.

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