Gear, wheels, brakes, struts

Nine procedures. Three of them can kill you if done wrong, and those three open the list.

Procedure 1 — Jack an aircraft (S5, R2)

1. Check the manual for jack points, jacking weight, and any configuration required.
2. Check the surface: level, firm, indoors or with wind within limits. Soft ground is how aircraft come off jacks.
3. Use rated jacks with the correct adapters, positioned squarely on the jack points.
4. Brief everyone — who is jacking, who is watching, who calls stop.
5. Raise evenly and slowly, watching all points.
6. Fit stands or safety collars as it rises, not afterwards.
7. Nobody under the aircraft. Not to look, not for a moment.
8. Lower in the reverse order, evenly.

Check — stands or collars are in place before anyone approaches the aircraft. If the answer to "what is holding it up" is "the jacks", nobody goes near it.

Failure — jacking on soft or sloping ground. It looks fine until the aircraft is up.

Procedure 2 — Remove a wheel (S12, R1)

The step order here is the difference between a routine job and a fatality.

1. Jack the aircraft (Procedure 1).
2. Deflate the tire completely — remove the valve core and confirm it is fully deflated.
3. Only then consider through-bolts. Never slacken a through-bolt on an inflated wheel.
4. Remove the axle nut per the manual, supporting the wheel.
5. Remove the wheel, keeping bearings clean and identified.
6. Separate the wheel halves only after confirming, again, that the tire is deflated.

Check — push the valve and confirm no air. Say it out loud. A wheel assembly is a pressure vessel and a separation is explosive (AF-E Concepts §1).

Failure — assuming a tire is flat because it looks flat. A tire can look deflated and hold enough pressure to separate a wheel.

Procedure 3 — Inspect wheels, brakes, bearings and tires (S7, S13, S27)

Tires: tread depth against limits, cuts, bulges, sidewall condition, flat spots, exposed cord, weather checking, and correct inflation measured cold. Under-inflation is the commonest cause of tire failure and it is invisible by eye.

Wheels: cracks — especially at the bead seat and bolt holes — corrosion, damage to the bead seat area, and correct through-bolt torque.

Bearings: clean, inspect for spalling, pitting, brinelling and discoloration; check the races; repack per the manual.

Brakes: lining thickness against limits, disc thickness and condition, warping, glazing, scoring, and evidence of leakage or overheating.

Check — measure, do not judge. Lining thickness, disc thickness and tread depth all have numerical limits, and eye estimates pass parts that are out of limits.

Failure — inspecting a tire only where it is visible. Rotate it — the flat spot or the cut is usually on the part that was on the ground.

Procedure 4 — Replace brake linings (S8)

1. Check wear limits and confirm replacement is required.
2. Note the orientation and arrangement before disassembly.
3. Remove old linings and inspect the backing plates and disc.
4. Fit new linings per the manual — correct rivets, correct order, correct torque or set.
5. Reassemble, torque per the manual.
6. Bed in per the manufacturer's procedure if one is specified.
7. Check for drag with the wheel free.

Check — spin the wheel. It must turn freely with the brakes released. A dragging brake overheats, wears rapidly, and is a fire risk on landing.

Procedure 5 — Bleed a brake system (S10)

1. Confirm the correct fluid (AF-F Procedures Procedure 1).
2. Follow the manual's method and sequence — some systems bleed from the bottom up, some from the top down, and doing it the wrong way traps air.
3. Bleed until fluid runs clear and free of bubbles.
4. Keep the reservoir topped throughout.
5. Check pedal feel and travel.

Check — firm pedal, consistent over several applications. A pedal that firms with pumping means air remains; a pedal that sinks under steady pressure means a leak, not air (AF-E Concepts §4).

Procedure 6 — Service an air/oil shock strut (S9, S15)

1. Jack the aircraft so the strut is fully extended and unloaded.
2. Discharge the gas completely — remove the valve core and confirm.
3. Compress the strut fully and fill with the specified oil to the specified point, per the manual.
4. Extend, and charge with the specified gas — dry nitrogen — to the specified pressure or to the specified extension dimension.
5. Measure the extension with the aircraft on its wheels at the stated weight, and compare against the manual.
6. Check for leaks.

Check — the extension dimension is the answer, not the pressure alone. A strut at the right pressure and the wrong extension has the wrong oil quantity (AF-E Concepts §3).

Failure — slackening anything before the gas is discharged. R5. Confirm the core is out and the strut is at zero.

Procedure 7 — Service a shimmy damper, and diagnose shimmy (S17, S28)

Servicing: check fluid level and condition per the manual, check for leaks and for free movement without slop, refill with the specified fluid, purge air.

Diagnosing shimmy — work the contributors in order (AF-E Concepts §5):

1. Tire — condition, balance, inflation, wear pattern.
2. Wheel bearings — adjustment and condition.
3. Torque links — wear at the bolts and bushings, and free play.
4. Strut — extension and servicing state.
5. Shimmy damper — fluid, function, mounting.
6. Geometry — alignment and trail.

Check — measure the play at each contributor rather than feeling for the loose one. Shimmy is often several small clearances combining, and replacing the damper on its own frequently does not fix it.

Procedure 8 — Gear retraction check (S6, S25, S26)

1. Aircraft on jacks with stands fitted (Procedure 1).
2. Clear the sweep of every gear leg, and brief everyone. Nobody in the sweep (R6).
3. Warn audibly before actuation, every cycle.
4. Cycle the gear, watching for sequence, timing, full travel, door clearance and locking.
5. Check position indication and warning against actual gear position at each stage.
6. Check down-lock and up-lock engagement, and adjust switches per the manual (S25, S26).
7. Check the emergency extension system per the manual.

Check — indication must match reality at every stage, including intermediate ones. An indicator that reads down when the gear is down but also reads down mid-travel is not a working indicator.

Failure — cycling gear with someone in the sweep. The gear moves faster than people expect and it does not stop.

Procedure 9 — Replace master cylinder packings (S20)

1. Relieve system pressure (AF-F Procedures Procedure 0).
2. Drain and remove the cylinder, capping lines.
3. Disassemble, noting the order and orientation of every part.
4. Inspect the bore for scoring, pitting and corrosion. A scored bore will not seal on new packings.
5. Fit new packings and backup rings per AF-F Procedures Procedure 2 — backup ring on the low-pressure side.
6. Reassemble, install, bleed (Procedure 5), and check.

Check — the bore condition decides whether new seals will work. Fitting packings into a scored bore produces a cylinder that leaks again shortly.

The checks, collected

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