100hrs/annual inspection C 172 - what effort

A 100hr service doesn’t have a specific meaning, because most light piston GA planes don’t have one. I think the SR20/22 have a 100hr service but they still need an oil change at 50hrs.

There is a 100hr service on an N-reg if it is used for paying passengers or you are training other people in the plane. That one is normally close to an Annual.

An Annual takes about 4 man-days, on most planes like a C172, C182, all the way through to a TB20. It is mostly inspection of lots of stuff. Retractables need a proper greasing of the landing gear (which almost no company does, despite ticking all the boxes) and that is about 0.5 man-day to do fully.

Any remedial work is additional, of course.

In most cases, the 100-hour check program for light piston aeroplanes is exactly the same as the annual. I’d also budget 3 to 4 man-days, unless you have ADs to take care of, in which case it can be a lot more…

This the 100 hr inspection for a 1954 Cessna 180 I once owned:

100 HOUR INSPECTION
Before beginning the inspection, the shop foreman or mechanic runs the engine to check for ignition drop, generator charging rate, oil pressure variation, and to check smoothness and general operation of the engine, propeller, controls, and indicators. He records these facts as an aid to the mechanic. The inspection consists basically of the following procedures:

I. Remove all inspection plates and fairings, consisting of the following:
1. Remove lower half of wing root fairing (both sides).
2. Remove the eight inspection plates on underside of each wing.
3. Remove the two inspection plates on cabin top adjacent to the wing flaps.
4. Remove tail group fairing and disconnect stinger.
5. Remove the inspection plate on the underside of fuselage just forward of the stabilizer.
6. Remove the three inspection plates on the belly of the fuselage.
7. Remove rear seat back and front seats.
8. Open upholstery headliner zipper.
9. Remove scuff plates and rudder pedal shields, roll back floor covering and remove round inspection plates above landing gear bulkhead.
10. Remove adjustable stabilizer control wheel cover and rear center tunnel cover plate.
11. Remove inspection plates just forward of the rear seat.
12. Remove curtains at the aft end of the baggage compartment for access to cables, bellcranks, pulleys, battery, and radio units.
13. Open landing gear fairing at fuselage.
14. Remove wheel and brake fairings.

1. Remove engine cowl and propeller spinner.
2. Visually check engine for oil leaks.
3. Drain oil from engine, clean oil screen located on rear side of accessory case, and refill with new oil of the recommended weight.
4. Wash down engine and propeller.
5. Remove heater muffs. Inspect mufflers and exhaust stacks for possible cracks.
6. Check carburetor air and heater hoses for holes, collapsed tubes, burning, and security of mounting.
7. Check magnetos for condition and security of mounting. Check timing of magnetos, if required (26° BTC).
NOTE
Since the engine timing marks are covered by the spinner adapter, the use of a top center gage and clamp-on type timing disc is recommended for timing the engine—otherwise, the propeller must be pulled in order to use the engine timing marks for timing the engine.
8. Check cylinder base nuts for tightness.
9. Remove spark plugs, clean, set gap (.016—.018), and test. Check condition of copper gaskets.
10. Check engine mount bolts for security and engine mount tubes and gussets for condition.
11. Check all wires forward of the firewall.
12. Check all engine controls for travel and free movement.
13. Remove and clean fuel strainer bowl and screen.
14. Clean carburetor air screen, re-oil, and reinstall.
15. Check cowl flap mechanism for security and condition.
III Propeller Check
1. Check propeller track.
2. Check propeller blades, hubs and blade clamps for condition and rework any nicks or abrasions as necessary.
3. Check guide blocks for cracks and wear
4. Check jamb nut on blade travel-stops for tightness.
5. Check piston and blade clamps for evidence of leakage.
6. Check propeller tightness on shaft
7. Examine dowel pins to make sure they have not shifted.
8. Grease propeller at grease fittings.
9. Clean and install engine cowl and propeller spinner.

1. Check front and rear wing bolts attaching wing to fuselage (both wings).
2. Check strut bolts for security (both wings).
3- Check all wing control surfaces for freedom of movement and bolts for security.
4. Check aileron bellcranks and cables for security, conditions, and proper safetying (both sides).
5. Check flap bellcranks, tracks, and pulleys and cables for security, condition and proper safetying (both sides).
6. Drain wing fuel tank sumps and resafety — check for fuel leaks.
7. Check pitot tube for cleanliness and freedom from obstructions.
8. Check landing light window for cracks and cleanliness.
9. Check navigation lights for damage.
10. Check flap travel (0° to 38° +2°-1° and aileron travel (20° ±2° up and14° ±2° down).

1. Check both stabilizer and vertical fin for possible damage.
2. Check attaching bolts on both fin and stabilizer for security.
3. Check rudder and elevator attaching bolts for security and surfaces for freedom of movement.
4. Check elevator and rudder hinges.
5. Check surface travels. Elevator 25°±1° up and 22° ±1° down from streamlined with the stabilizer in its full-down position. Rudder 24° ±1° left and right. Adjustable stabilizer travel is fixed, but the mechanism should be checked to see that the stabilizer moves its full range between the fixed stops.
6. Check elevator and rudder bellcranks.
7. Check balance weights for security.
8. Check navigation light for damage.
VI. Tail Gear.
1. Hoist tail gear above floor. Shake tail gear spring to check for any sign of looseness and visually inspect fuselage attachment. Tighten any loose bolts and replace rubber bushings if necessary.
2. Lubricate tailwheel fittings.
3. Inspect tailwheel steering mechanism and tire inflation.
VII. Cabin Section.
1. Clean and check condition of:
a. Plexiglas windshield and windows.
b. Upholstery — Vacuum if possible.
c. Instrument glasses.
d. Ash trays.
e. Metal cabin trim.
f. Instrument and control panels.
g. Decals, control panel lettering, and compass correction card.
2. Check operation and condition of:
a. Door latches.
b. Window opening mechanism.
c. Manifold heating system valves, ducts and louvers.
d. Control knobs.
e. Safety belts.
f. Ventilating system.
g. Seat adjustment mechanism.
3. Check the primer for leakage and security.
4. On rudder bar and control tee assemblies check:
a. Security of mounting.
b. Cable connection points,
c. Pulley installations
d. Rudder return springs
5 On battery check:
a. Electrolyte level and specific gravity (1.310—1.226)
b. Cables for security and condition.
c. Battery security.
d. Cleanliness of battery box and terminals — clean off and neutralize spilled fluid with soda water solution and rinse with clear water.
6. Drain sediment and water from fuel line at plug located on the belly of the airplane.
VIII. Main Landing Gear and Brakes.
1. Hoist or jack up airplane to remove weight from landing gear. Shake landing gear and wheels for any sign of looseness and visually inspect fuselage attachment. If necessary, tighten landing gear bolts and wedges. With airplane in 3-point position on the floor visually inspect landing gear spring leaf for cracks. (Remove landing gear wheels and pack with grease at first 100 hours and every 500 hours thereafter unless otherwise designated by owner.)

2. Operate brakes and feel for sponginess. Bleed and refill brake system if necessary. Check brake linings for wear within permissible limits.
3. Set parking brake and check exposed lines and hoses for deterioration and evidence of leakage of hydraulic fluid.
4. Examine tires for proper inflation, wear, cuts and blisters. Uneven or excessive wear may indicate need for re-alignment of wheels.
IX. Electrical System.
1. Check electrical system by operating the lights, starter, and all accessories which are incorporated in the electrical system.
X. Visual Check for Exterior Surfaces.
1. Clean exposed surfaces.
2. Check:
a. Condition of exposed aluminum surfaces.
b. Airspeed static source holes on each side of fuselage for stoppage.
c. Evidence of leaking fuel or oil — determine cause.
d. Condition of decorative paint and all markings.
XI. Re-cowl the engine and install propeller spinner. Replace all inspection plates, fairings and seats. Check cowl flap travel. Rig cowl flaps in accordance with figure 28.
XII. Run engine as in preliminary run-up to check for ignition drop, generator charging rate, oil pressure, smoothness, and general operation of engine, propeller, controls, and indicators.

Cessna defines the 100h check precisely in the maintenance manual section 2 and it’s the annual that is a 100h check, not the other way around for a Cessna.

A C172 can be done in one man day if you’re experienced and know the aircraft well, otherwise two. This is without any extraordinary problems obviously.

When working with two (i.e. A/P + myself), I can do my TR182 in two days when the extra work is very limited, otherwise three days. That includes all Cessna/CAA mandated tasks plus some extra that come out of experience.

Retractables need a proper greasing of the landing gear (which almost no company does, despite ticking all the boxes) and that is about 0.5 man-day to do fully.

What happens with all your grease? Mine stays in place and the check consists of verifying that there is sufficient grease. If you re-grease, you have to wash out the existing grease which is a big job but what for? I think I’ve added grease to the landing gear only once since I bought it because there is plenty.

There is a gradual ingress of dirt into the grease.

Also any wear particles remain in place and act as a grinding paste to accelerate wear.

Yes – re-greasing requires dismantling which is why almost nobody wants to do it unless you pay extra.

This is one reason why the TB20/21 GT is better than the pre-GT because it has a lot of grease nipples which avoid the need for dismantling most of the landing gear.

Absolute minimum 18 hours for a 172, but you’ll never actually do it in that, as some things won’t come apart as easily as they should, and you will stop to fix things along the way.

The SR22 has no 100 h if it is registered “G”. It has 50 h inspections only and the annual – and a 150 h if you fly more.

If it is registered “D” it will have 50 and 100 inspections, and 100 h inspection has to be done every year, regardless of the hours flown. Most owners (of all types) who fly less than 100 h try to do annual and 100 h inspecetion together, and most shops offer a discount for that, allthough some don’t.