19.4 Before-Takeoff Check, After-Landing, and Securing the Airplane
Key Takeaways
- The magneto check verifies that each ignition system fires independently; the AFM sets both the maximum RPM drop and the maximum allowable difference between the two magnetos.
- No RPM drop at all during the magneto check suggests a broken or grounded P-lead, which leaves that magneto hot — the propeller must then be treated as live even with the switch off.
- The carburetor heat check should produce an RPM drop, confirming that warm, unfiltered air is actually reaching the carburetor.
- Do not begin after-landing checks until the airplane is completely clear of the runway, past the runway holding position marking.
- Shut down with the mixture at idle cutoff so no combustible charge remains in the cylinders, and record every discrepancy in the maintenance record rather than passing it along verbally.
The run-up is a diagnostic, not a ritual
PA.II.F.K1 asks for the reasons for checking each item and for detecting malfunctions. Position the airplane clear of the runway and of other aircraft, on a firm surface so the propeller does not ingest gravel, and — where practical — nose into the wind for cooling.
| Check | What it is actually testing | The malfunction it detects |
|---|---|---|
| Magneto check at the AFM RPM | Each ignition system firing on its own, since the engine has two independent magnetos and two plugs per cylinder | Excessive RPM drop (fouled plug, bad lead, mistimed magneto); excessive difference between magnetos; a rough run on one magneto |
| No drop at all on a magneto | The P-lead grounding path | A broken or grounded P-lead — that magneto is hot and the engine can fire even with the switch OFF |
| Carburetor heat | That warm, unfiltered air is reaching the carburetor | No RPM drop means the heat is not getting there — the anti-icing system is inoperative (Section 7.2) |
| Engine instruments | Oil temperature and pressure in the green, ammeter charging, suction or vacuum in range, fuel flow normal | A failing alternator, a failing vacuum pump before you need the gyros (Section 12.2), a cooling problem |
| Flight controls free and correct | Full, unobstructed travel in the correct sense | A jammed control, a control lock left in, a reversed cable after maintenance |
| Flight instruments set | Altimeter to the current setting, heading indicator aligned to the magnetic compass, attitude indicator erect, VSI near zero | A gyro that will not erect, an altimeter outside tolerance, precession beyond limits |
| Configuration | Trim set for takeoff, flaps set, fuel selector on the proper tank, mixture set for the field elevation | A trim setting or fuel selector that would produce a control or power surprise on the roll |
| Doors, belts, seats | Latched, fastened, and locked | A door that pops open on climb-out, a seat that slides aft on rotation |
Finish with a departure briefing spoken out loud: the abort point on the runway, what you will do if the engine quits on the roll (throttle idle, brakes, stop straight ahead) versus after liftoff at low altitude (lower the nose, land more or less straight ahead, small turns only to avoid obstacles — Section 18.3), the initial heading and altitude, and the first frequency. Deciding this on the ground is the whole point.
After landing — clear the runway first
The rule that matters: do not begin after-landing checks until the airplane is completely clear of the runway, meaning past the runway holding position marking. Heads-down time on an active runway is how incursions and collisions happen. At a towered airport, stay on the tower frequency until instructed to change.
Once clear: flaps up, carburetor heat cold, trim reset, landing light and strobes as appropriate, transponder per local procedure, and then the taxi clearance.
Shutdown, securing, and the postflight inspection
Task XII.A covers airplane shutdown, securing, and postflight inspection, plus documenting discrepancies.
- Mixture to idle cutoff stops the engine by starving it of fuel, so no combustible charge is left in the cylinders. Shutting down with the magneto switch instead leaves raw fuel where it can fire on a later propeller movement.
- Magnetos off after the propeller stops, then master off, then the key removed. Treat the propeller as live regardless — especially if the magneto check showed no drop.
- Secure the airplane: control lock installed, chocks and a three-point tie-down (both wings and the tail) if it will sit outside, pitot cover on, cowl plugs in, fuel selector per the AFM, and the doors and windows latched. Park into the wind where the ramp layout allows.
- Postflight inspection is a walk-around with fresh eyes: new oil streaks, a fuel stain, a nicked propeller, a flat-spotted tire, a hangar-rash dent. The discrepancy you find on the ramp is the one the next pilot does not discover at 1,000 feet.
- Documenting discrepancies (PA.XII.A.K2) means writing them into the squawk sheet or maintenance record — not mentioning them to whoever is behind the desk. A verbal report leaves no record, does not reach the mechanic reliably, and does not discharge your responsibility. If an item is deferred, the 91.213(d) path requires it to be removed or deactivated and placarded "Inoperative" (Section 3.3).
- Refueling after the flight reduces overnight condensation in the tanks, which is the practical answer to water in the sumps — but check that the resulting fuel load still leaves a legal weight and CG for the next flight (Chapter 14).
During the run-up, the engine shows a 40 RPM drop on the LEFT magneto and no drop at all on the RIGHT magneto. What does the right-magneto indication most likely mean?
Applying carburetor heat during the before-takeoff check produces no change in RPM. What does this indicate?
Why is the engine shut down by moving the mixture control to idle cutoff rather than by turning the magneto switch off?