GRUMMAN AMERICAN
FOR TRAINING USE ONLY – SECTION 4
MODEL GA-7/COUGAR
NORMAL PROCEDURES
4-17
Issued: April 10, 1978
BEFORE TAKEOFF
WARM-UP AND GROUND CHECK
Check both oil pressure and oil temperature and ensure mixture controls are set to full rich.
PROPELLER CHECK
Check the propeller control system for proper operation. Advance the throttles to give an engine speed of 2200
RPM. Move the propeller control from high RPM to low RPM and back to high RPM positions. The normal RPM
drop is from 150 to 200 RPM. Full feathering check of the propellers on the ground is not recommended, but the
feathering action can be checked by running the engine at 1500 RPM, then momentarily pulling the propeller
control into the feathering (full aft) position. Do not allow the RPM to drop more than 500 RPM.
MAGNETO CHECK
A proper magneto check is important. Factors other than the ignition system affect magneto drop off. They are
load-power output, propeller pitch, and mixture strength. With the propeller at minimum pitch angle, set the
engine to 1800 RPM. The mixture control should be in the full rich position.
Switch from both magnetos to one and note drop-off. Return to both until engine regains speed. Switch to the
other magneto and note drop-off. Return to both. The drop-off should not exceed 175 RPM or 50 RPM between
magnetos. A smooth drop-off past normal is usually a sign of a too lean or too rich mixture. Perform magneto
check on both engines.
To minimize plug fouling, do not operate on a single magneto for a long period. A few seconds is usually sufficient
to check drop-off.
ELECTRICAL SYSTEM CHECK
NOTE
When the master switch is OFF, the alternators and the battery are disconnected
from the electrical bus. The Master Switch must be ON before either alternator,
battery, or external power can power the electrical bus.
To run a functional check of the battery and alternator circuits, use the following procedure:
1.
Set both engines at 1800 RPM with some electrical equipment on.
2.
Turn left alternator switch off.
3.
Right alternator current meter reading will increase and left alternator failure light will illuminate.
4.
Turn left alternator switch on. Turn right alternator switch off.
5.
Left alternator current meter reading will increase and right alternator failure light will illuminate.
6.
Turn right alternator switch on.
Except for the landing gear the circuit breakers cannot be pulled to deactivate electrical circuits. The circuit
breakers will automatically open in case of a current overload. The breaker can be reset by pushing in.
A simple last minute recheck of important items should include a quick glance to see that all switches are ON, the
mixture and propeller controls are forward, all flight controls have free and correct movement, and the fuel
selectors are properly positioned.
A mental review of all single-engine speeds, procedures and field length required should be made prior to takeoff.
