Jaybird180
Final Approach
When I did my transition to the DA-40 (par example) the pre-takeoff and the pre-landing checklists both include the titled procedure. I've always wondered why.
Reading Deakins' article on Mixture it brought the question back to mind on why the procedure exists.
He says:
Can someone help me understand why? Why not just leave the engine-driven pump to do the job? The procedure also is there on other low-wing planes.
Reading Deakins' article on Mixture it brought the question back to mind on why the procedure exists.
He says:
It's All in the Mixture
How does this translate into the gasoline-powered, spark-fired, internal combustion engines found in our airplanes (and also in tractors, lawn mowers, and cars)? For purposes of this article, I'll limit my discussion to normally-aspirated engines, leaving turbocharged ones for a future column.
In the engine that powers my Bonanza (a TCM IO-550), if I flip the boost pump to high with the mixture rich, I can literally "flood" the engine and kill it, even at takeoff or climb power settings. (Update Oct. 2005: This column was written in 1999, when I believed that to be true. Alas, it is not completely so. At low power settings, it is true, and illustrates the principle nicely. But most of these engines -- including mine -- tolerate the boost pump very well at high power settings. Indeed, the boost pump can be your friend if taking off with hot fuel in the tanks, or if you climb rapidly, as with the Turbo'd aircraft.)
Any malfunction that pumps "too much" fuel into the combustion chamber (relative to the air) will do the same thing. The fuel is flowing, the spark is sparking, and the airspeed is still turning the prop, but there's just too much fuel and not enough air. Flip the boost to "Low" or "Off" or lean it out with the mixture control and the engine will run again. Given the correct fuel flow, air flow and spark, it must start and run.
Can someone help me understand why? Why not just leave the engine-driven pump to do the job? The procedure also is there on other low-wing planes.