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BACK TO BASICS
MICHAEL CHURCH
MARCH 1997

LANDINGS AND EMERGENCIES


So far, the management of the constant speed option has been covered in these columns for all flight conditions except approach, landing, and emergencies.

Prop pitch and engine RPM have little effect on landings, but care needs to be taken in case a go-around becomes necessary. Applying full throttle--say 30"--at 2200 RPM won’t deliver anything close to full power, so pre-landing checklists should always include "PROP" as one of their steps to ensure the propeller control is advanced in anticipation of future high power demands. Ideally, this action, like all pre-landing steps, should be done well away from the airport to assure its completion before the distractions and workload of entering the pattern begin to interfere.

Noise--for people on the ground--is definitely a factor in this step. If you remain at manifold pressure and increase RPM, noise levels naturally go up. A simple solution is to delay prop advance until you have reduced power for the descent: once you are below 20" of MP, advancing the prop control will have little effect on actual RPM, so added noise will be minimal. As an added bonus, delaying to this point will also prevent the sudden change in RPM and cabin noise you get if you make a prop change while under normal power.

If you don't have a customary pre-landing checklist, I'd like to recommend one: an excellent choice is BCGUMPS (“bee-cee--gumps”)--Boost pump, Cowl flaps, Gas, Undercarriage, Mixture, Prop, Seat belts and Switches. A quick run through this list on the approach will get most airplanes ready to land with minimal distraction from traffic, arrival procedures and communications.

EMERGENCIES
As with most added equipment, the constant speed prop gives the pilot one more system that can go wrong--one more area that requires vigilance.

Mentioned very early in this series was the necessity of extra care during takeoff. After checking the tach at the beginning of the roll to make sure the engine is making full expected power, you must continue to monitor RPM as you accelerate. In single engine airplanes, governor failure shows up as engine overspeed--if you see it, you should abort.

You should also allow for governor system failure at later stages in the flight. When the governor fails, oil pressure to the hub will drop, and, because single engine mechanisms are designed to default to LOW PITCH, run-away RPM will again be the symptom. CFI’s are fond of pointing out that the reasoning behind this design is to make go-arounds and climbs possible even after governor failure. What you may not have been told is that with the blades stuck at low pitch, any in-flight application of full power will immediately overspeed the engine--at climb speeds, by hundreds of RPM.

You might be forced to put up with an overspeed for a short while to meet the needs of a go-around, but if you stick with it too long, you risk creating another emergency--engine damage--on top of what you already have. The only solution is to reduce power, and you will be dismayed to discover that by the time you get RPM below redline, you will have significantly worse performance than could be normally expected from a fixed pitch prop in the same circumstances. Plan accordingly: go-arounds should be a last resort in the event of governor failure.

That’s the whole picture: seven columns on a subject often dealt with in less than an hour by instructors doing the initial “high performance” sign-off. If there’s a lesson in that, it’s that the addition of each new system to an aircraft geometrically increases the study workload of the prospective pilot.

On a related subject: in the near future, I plan to revisit the general subject of RPM and manifold pressure.

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