Pre-takeoff Checklist
A recent query on the Cessna Pilots Association forum reminded me that I wanted to address the procedures prior to the takeoff. Frank Fisher and Paul Knapp contributed answers similar to my own procedures and I’ve edited them below and interspersed Mike Busch’s thoughts on the mag check. John Godwin at Pilots of America had some good thoughts on cycling the prop.
[JS] All of the engines that I’ve flown are happiest with aggressive leaning on the ground during taxi and runup. And by aggressive we mean that applying the throttle causes the engine to stumble. We paid for lots of plug cleanings before we learned that lesson.
[PK] For that same reason, at runup, I lean so far that if I push the throttle any farther forward the engine stumbles. This gives me a very, very lean mixture for runup which is more likely to indicate incipient problems than a richer mixture. And, it protects me from doing something stupid like taking off with a lean mixture at sea level.
[JS] You’ll need to enrichen the mixture a bit to get the RPM to the manufacturer specified run-up RPM—but you don’t need to go full rich. The engine is going to be running well below 65% power at the target RPM, so leaning is appropriate and gives you a better estimate as to how the engine will perform in flight. There should be some drop on each mag but no more than what the engine manufacturer specifies. If there is no drop, you may have an improperly grounded mag.
[MB] If you have an engine monitor you should focus primarily on the engine monitor, not the tachometer, when performing the mag check. What you should be looking for is all EGT bars rising and none falling when you switch from both mags to one mag. The EGT rise will typically be 50 to 100 degrees F, but the exact amount of rise is not critical. [JS] This occurs because the fuel takes longer to burn with just one plug and so is hotter when exiting the cylinder.
If you’re flying a plane with a constant-speed prop, you’ll want to cycle it. While you’re doing it look a the oil pressure. It should show little or no change if you have enough oil. The manifold pressure .. should show an slight increase because the pitch changed. And the RPM should show decrease verifying that the pitch changed.
Controls free and correct should have been tested just after engine start. The remainder of your flight instruments should have been checked during taxi (airspeed indicator for zero; attitude indicator erect and steady; altimeter for field elevation +/- 75′; turn coordinator banking in the direction of turns while the inclinometer slips inside and skids outside; heading indicator for proper tracking during turns; and VSI somewhere near zero.
[JS] Set the DG after it has a chance to stabilize. The magnetic compass and DG should be opposite the runway heading when taxiing parallel to the takeoff runway.
[PK] On my O-200, for runup I lean it to the point where it will run smoothly but if I push the throttle in any farther it will stumble. For taxi, my mixture is so lean that I couldn’t reach runup RPMs if I tried. If you can do your runup at your lean taxi setting, then you’re not leaning nearly enough. The goal in aggressive ground leaning is two fold: to protect the engine from lead deposits that form at cooler CHTs, but also to lean so far that there is absolutely no way you could inadvertently takeoff at that setting.
[JS] Just before I call for takeoff clearance I close the doors and windows and check that they’re locked, set the flaps if necessary, and put my hand on the mixture. Then I’m ready to go when given my clearance.