1973 Cessna 172M Deep Dive

The following is a detailed exploration of a specific aircraft model based on information from the POH, TCDS, and other resources.

Source materials:

• Pilot's Operating Handbook
• Type Certificate Data Sheet
• FAA ADs

Vacuum System

Fuel System

• Two fuel tanks, one in each wing
  • 21 gallons per side, 19 gallons usable
  • 42 gallons total, 19 gallons total usable
• Total usable fuel is 19 gallons per side, for a total of 38 gallons
• Fuel is gravity fed to the selector valve, then through a fuel strainer and then to the carburetor
• The fuel selector value should be used as follows:
  • BOTH for takeoff, landing, or anything maneuver involving prolonged slips/skids
  • LEFT or RIGHT for cruising flight

Electrical System

The electrical system consists of a 14-volt DC system, powered by an engine-driven alternator. A 12-volt battery is located on the left-hand portion of the firewall.

There are two buses, one for general electrical equipment, and on for electronic equipment. When the ignition/starter switch is turned on, a power contactor opens the electronic bus circuit, preventing harmful voltage from damaging the electronics.

The master switch consists of two halves:

• Left half controls the alternator connection to the system
• Right half controls the battery connection to the system

The ammeter will show a positive charge when the battery is charging, and a negative charge when it is discharging faster than the alternator can charge it.

There is an over-voltage system, which includes a warning light labelled HIGH VOLTAGE.

• When the light is on, the system has removed the alternator from the electrical system.
• If this occurs resetting the alternator (turning the master off then on), may reset the alternator in some cases.
• This can also be tested by momentarily turning off the ALT portion of the master.

Circuit Breakers

Most circuits are protected via "push to reset" circuit breakers on the front of the instrument panel. Exceptions are:

• Clock
• Hobbs meter
• Cigarette lighter

Lighting

Lighting consists of:

• Flashing red beacon
• Navigation lights on each wingtip
• Landing and taxi light in the front cowling
• Overhead dome light

Wing Flaps

Wing flaps are electrically operated by a motor in the right wing.

• The flaps operate in a 0° to 40° range.
• Full extension of the flaps takes approximated 9 seconds
• Full retraction of the flaps takes approximately 7 seconds
• The three-way switch can be returned to the center position once the flaps are up
• If side slips are used with full rudder deflection and flaps more than 30°, some elevator oscillation may be felt. However, this does not affect the control of the aircraft.

Heat and Ventilation

• Front cabin heat and ventilation are provided via outlet hoses under the pilots' feet.
• Rear cabin heat and ventilation comes from hoses which end on each side of the rear cabin at floor level
• Window defrost air is supplied by a duct leading from the cabin manifold

Seatbelts

• Shoulder and lap belts are provided for the front seats
• Lap belts are provided for the rear seats

Operations

Starting

• Open throttle 1/8" inch
• 1-2 strokes of primer should be sufficient in warm weather
• Up to 6 strokes may be necessary in cold temperatures
• If the engine is warm, no priming is required
• Oil pressure should be up within 30 second of starting in warm weather, or about 60 second in very cold weather. Otherwise, stop the engine

Cold-Weather Starting

• Prior to starting, pull the propeller through several times
• Use an engine preheater in extremely cold weather

Taxiing

• Carb heat should always be off for ground operations, as the intake air is unfiltered with carb heat on.

Takeoff

• When taking off at >3000' MSL, the mixture should be leaned for max RPM in the runwup prior to takeoff.
• Normal and obstacle clearance takeoffs are performed with wing flaps up
• 10° of flaps may be used for soft/rough fields, or where a minimum ground run is desireable.
  • In this case, use a obstacle clearance speed of 65 MPH
• Crosswind takeoffs are performed
  • With minimum flaps
  • Allow the airplane to accelerate slightly more than usually
  • Abruptly pull the airplane off the runway to prevent it settling back down

Climbs

• Climb at 80-90 MPH
• Mixture should be full rich below 3000' MSL
• Mixture should be leaned for max RPM and smooth engine operation above 3000'

Cruise

• Cruise between 65% and 75% power

Carbuerator Ice

Carb ice is evidence by an unexplained drop in RPM.

• It can redmedied by full application of carb heat.
• Afterwards, use the minimum amount of heat necessary to form icing.
• Use full carb heat during flight in heavy rain
• In extremely heavy rain, partial carb heat and partial throttle may be needed to maintain power

Stalls

• The stall horn will come upon around 5-10 MPH above stall in all configurations

Spins

Spin recovery is performed:

1. Retard the throttle to idle.
2. Apply full opposite rudder in the opposite direction of the turn.
3. Move the control wheel forward in a brisk motion.
4. Neutralize the rudder as the rotation stops, and make a smooth recovery from the dive

Landings

• Short field landings are done with power off, 40 ° of flaps, and approximately 69 MPH airspeed.
• Crosswind landings should be done with minimum flap setting
• With average pilot technique, a direct crosswind of 15 knots can be handled safely.

Go-Arounds

1. Apply full power
2. Reduce wing flaps to 20°
3. Once a safe altitude is reached above obstacles, retract the reset of the flaps.

Emergency Procedures

Electrial Power System Malfunctions

• Excessive rate of charge
  • The ammeter should show less than two needle-widths of charge once established in cruise flight.
  • If the charge reaches 16 volts, the protection system will shut off the alternator
• Insufficient rate of charge
  • Usually caused by a alternator failure, or failure of the alternator belt
  • In this case, load-shed off the battery and land

Rough Engine or Loss of Power

• Gradual loss of RPM is usually indicative of carburetor ice
• Roughness could also be related to an improperly set mixture
• Spark plug fouling is indicated by rough, low power engine when operating on one set of magnetos
  • If the problem persists, try operating a leaner mixture

Magneto Malfunction

Sudden engine roughness is usually evidence of magneto problems. Switch from LEFT or RIGHT to determine which set is malfunctioning, then run on the good side. Land as soon as you can.

Low Oil Pressure

• Can be caused by th oil pressure gauge malfunctioning
• A leak in the line to the gauge isn't necessarily an emergency, as there is an orifice that prevents a sudden loss of oil from the engine sump
• A loss of pressure and a rise in oil temperature is reason to suspect an imminent engine failure:
  • Reduce power and select a suitable forced landing field

Engine Fire While Starting

• Continue cranking the engine until start
• If the engine starts, run at 1700 RPM for a few minutes before shutting down
• If the engine does not start, continue cranking until fire extinguishers can be obtained

Engine Fire in Flight

1. Mixture to idle cutoff
2. Turn off fuel selector valve
3. Master switch off
4. Establish a 120 MPH glide
5. Close cabin heat
6. If fire does not extinguish, find an airspeed that results in an incombustible mixture
7. Execute a forced landing

Engine

150 HP Lycoming O-320-E2D

Oil

• Oil type: SAE 20
• Do not operate with less than 6 quarts of oil
• Fill to 8 quarts for extended flights

Landing Gear

• Tire Pressures:
  • Nose Wheel: 231 PSI
  • Main Wheels 29 PSI
• Nose gear Shock:
  • Keep filled with hydraulic fluid and inflated with air to 45 PSI

Weight and Balance

Station	Weight	Arm (in.)	Moment (lbs.-inches / 1000)
Aircraft Empty Weight	lbs	in.	55.975
Oil	lbs	in.	-0.200
Fuel (at 6 lbs/gal)	gallons	in.	10.944
Pilot	lbs	in.	5.550
Copilot	lbs	in.	5.550
Rear Passenger 1	lbs	in.	10.950
Rear Passenger 2	lbs	in.	10.950
Rear Baggage	lbs	in.	14.250
Total Loading	2389.50 lbs	47.70	113.97

Speeds

• V_x: 74 MPH
• V_y: 90 MPH
• V_y (10,000' MSL): 79 MPH
• V_A: 112 MPH
• V_N0: 145 MPH
• V_FE: 100 MPH
• V_NE: 182 MPH
• Maneuver entry speeds:
  • Chandelles: 120 MPH
  • Lazy 8's: 120 MPH
  • Steep Turns: 112 MPH

Applicable Recurring AD's

Serial #: 17261958

• 5/13/2011, 2011-10-09 6/17/2011: Seat Rails and Roller Housing Inspections