Type Rating Knowledge — Cessna 172S NAV III

Landing gear, ground control and brakes

How a Cessna 172S is steered, stopped and moved on the ground: the spring bungee that gives the nosewheel its 10 degrees, the extra 20 that only differential braking can buy, the spring steel and air/oil struts that absorb the landing, and what to do when one brake goes soft.

Take the interactive lesson →

Ground control and taxiing

Ten degrees from the pedals, thirty with a brake

Ground steering comes from the rudder pedals: left pedal to steer left, right pedal to steer right. Pressing a pedal works a spring loaded STEERING BUNGEE connected between the rudder bars and the nose gear, which turns the nosewheel through an arc of approximately 10° each side of centre. That is all the pedals alone will give you. Applying left or right brake increases the turn to up to 30° each side of centre — so on a 172S, a tight taxi turn is a braking manoeuvre, not a steering one. The bungee is worth noticing for a second reason: it is a spring, so nosewheel steering is soft and slightly indirect by design, rather than the rigid linkage a nosewheel-steering tiller would give.

RUDDER PEDALS — Rudder/brake pedals, pilot and copilot sets interconnected — rudder, nosewheel steering and brakes all come from here.
STEERING BUNGEE — Spring loaded steering bungee between the rudder bars and the nose gear — turns the nosewheel roughly 10° each side of centre.
L MASTER CYL — Left brake master cylinder, attached to the pilot-side left rudder pedal — pressed at the top of the pedal, not the whole travel.
R MASTER CYL — Right brake master cylinder, attached to the right rudder pedal.
PARKING BRAKE — Parking brake handle under the left side of the instrument panel — set the brakes with the pedals first, then pull the handle aft and rotate it 90° down.
NOSE GEAR — Steerable nosewheel on an air/oil shock strut. Never turn it more than 30° either side of centre under tow — structural damage to the nose gear can result.
L BRAKE LINE — Hydraulic line from the left master cylinder to the left main wheel brake.
R BRAKE LINE — Hydraulic line from the right master cylinder to the right main wheel brake.
L DISC BRAKE — Single-disc hydraulically actuated brake, inboard of the left main wheel, on a tubular spring steel main gear strut.
R DISC BRAKE — Single-disc hydraulically actuated brake, inboard of the right main wheel.

Redrawn from POH 172SPHBUS §7, Ground Control / Landing Gear System / Brake System — structure restated, not traced. C172S NAV III.

You need 25° of nosewheel deflection to make a turn. What gets you there?

Rudder pedal plus brake on the inside wheel. Right. The pedals give about 10° each side; differential braking takes the turn out to as much as 30°. Above 10°, braking is doing the work.

Moving it by hand, and the 30° that breaks things

By hand, use a towbar on the nose gear strut. If there is no towbar and the aeroplane must be pushed, push on the WING STRUTS — never on the vertical or horizontal tail surfaces. If it is towed by vehicle, never turn the nosewheel more than 30° either side of centre: past that, structural damage to the nose gear can result. Note that the 30° limit is the same number as the maximum steering deflection, so the aeroplane can be steered to its own tow limit but not beyond it. The minimum turning radius, using differential braking and nosewheel steering, is about 27 feet. For tighter than that, the aeroplane can be rotated around either main wheel by pressing down on a TAILCONE BULKHEAD just forward of the horizontal stabilizer to lift the nosewheel — on the bulkhead, not the skin between bulkheads, and not on the stabilizer itself, which the POH specifically does not recommend.

A tug driver asks how far the nosewheel can be turned while towing. What do you tell them?

No more than 30° either side of centre. Right — and it matters, because exceeding it can damage the nose gear structurally. It is the one number to say out loud to somebody towing your aeroplane.

How do you get the aeroplane round tighter than its 27-foot minimum radius?

Press down on a tailcone bulkhead just forward of the horizontal stabilizer to lift the nosewheel, and rotate it about a main wheel. Right — and it must be a bulkhead, not the skin between them, and not the horizontal stabilizer, which the POH says is not recommended.

The gear, the brakes and the parking brake

Spring steel at the back, air and oil at the front

The gear is tricycle: a steerable nosewheel and two main wheels, with wheel fairings standard on all three. Shock absorption is deliberately different at each end. The main gear legs are TUBULAR SPRING STEEL — they have no oleo, no fluid and nothing to service; they absorb a landing by bending and returning, which is why a firm 172 landing produces that characteristic springy rebound. The nose gear is an AIR/OIL shock strut, which does have a servicing state and can be flat. Each main wheel carries a hydraulically actuated disc brake on its inboard side. The fairings are not purely cosmetic either: POH Section 1 notes speed fairings are worth about 2 knots.

What absorbs the shock of a landing on a 172S?

Tubular spring steel legs on the mains, and an air/oil strut on the nose. Right — and the asymmetry matters in practice: the mains cannot be "flat", while the nose strut can be, and a flat nose strut is a preflight finding.

One master cylinder per pedal, and no crossfeed

Each main wheel has a single-disc hydraulically actuated brake, and each brake is connected by its own hydraulic line to a master cylinder attached to a rudder pedal. Brakes are applied by pressing the TOP of the pedals — the pilot’s left and right set and the copilot’s are interconnected, so either seat can brake. There is no crossfeed and no shared reservoir pressure between left and right: they are two independent circuits that happen to share your feet. That is the structural fact behind the one-brake-failed technique later in this unit. The parking brake is a handle under the left side of the instrument panel, and the order matters: set the brakes with the pedals FIRST, then pull the handle aft and rotate it 90° down.

What is the correct order for setting the parking brake?

Set the brakes with the pedals, then pull the handle aft and rotate it 90° down. Right. The handle holds pressure you have already made with your feet — it does not generate any of its own.

When the brakes go wrong, and what to do about it

The symptoms of impending brake failure are worth recognising before they matter: a gradual decrease in braking action after applying the brakes, noisy or dragging brakes, soft or spongy pedals, and excessive pedal travel with weak braking. Any of these means the brake system needs immediate attention. In the moment, the POH gives three specific actions. If braking action decreases during taxi or landing roll, let up on the pedals and then reapply with HEAVY pressure. If the pedals become spongy or travel increases, PUMPING the pedals should build braking pressure. And if one brake becomes weak or fails, use the other brake sparingly while holding opposite rudder as required to offset it — sparingly, because a single brake used hard is also a yaw input, and the correction is what keeps you straight.

The brake pedals have gone spongy and travel further than normal. What does the POH say to do?

Pump the pedals to build braking pressure. Right — spongy pedals and increased travel are the pumping case. Note it is a different answer from "braking action decreasing", which calls for releasing and reapplying with heavy pressure.

Ground handling and brake numbers (POH 172SPHBUS §7)
Item	Value
Nosewheel steering, pedals alone	≈10° each side of centre
Nosewheel steering with differential braking	Up to 30° each side of centre
Maximum nosewheel angle under tow	30° either side of centre
Minimum turning radius	≈27 feet
Main gear shock absorption	Tubular spring steel struts
Nose gear shock absorption	Air/oil shock strut
Brakes	Single disc, hydraulically actuated, one per main wheel

Why is there no "brake pressure low" annunciation on the G1000 for this system?

Because there is no powered hydraulic system to monitor — pressure comes from your feet, through a master cylinder per pedal. Right. The brakes are entirely manual hydraulics. There is no pump, no accumulator and no system pressure to report, which is why pedal FEEL is the instrumentation.