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Spongy brake pedals

Aviation Mechanic Airframe (AMA) practice question 8 of 17 on Landing Gear Systems. ACS element AM.II.E.K6 · difficulty: standard. Want to answer it in a timed quiz? Use the Aviation Mechanic Airframe (AMA) practice mode.

Question bank updated 2026-09-22

QUESTIONA pilot reports that the brake pedals feel spongy rather than firm. What is the most likely cause?

  1. AAir mixed in the brake hydraulic fluid
  2. BBrake linings worn beyond their wear limits
  3. CA brake disc warped by excessive heat
Show the answer and explanation

Correct answer: A. Air mixed in the brake hydraulic fluid

  • A — correct The handbook states that air in the brake system fluid causes the pedal to feel spongy, because air compresses under pressure while hydraulic fluid essentially does not.
  • B — incorrect Worn linings reduce braking effectiveness and are detected with the wear indicator pin or a direct measurement, but they do not make the pedal soft.
  • C — incorrect Discs must not be warped and an overheated disc can glaze, but that shows up as brake squeal and chatter, not as a soft pedal.

BACKGROUND

A common requirement of every aircraft braking system is that no air be mixed in with the hydraulic fluid. Air is compressible and hydraulic fluid essentially is not, so trapped air compresses when the brakes are applied and the pedal does not feel firm. The cure is bleeding, done either top down by gravity or bottom up by pressure, matched to the type of brake system and to the manufacturer's instructions. Brakes are bled whenever the pedals feel spongy or whenever the brake system has been opened. Systems using Goodyear master cylinders must be bled from the top down so that air trapped behind the master cylinder piston is removed.

STUDY TIP

Treat spongy pedals as an air-in-the-system symptom and pair it with bleeding; save lining wear and disc condition for effectiveness and squeal questions.

KEY POINTS

  • Air in the fluid compresses and makes the pedal feel spongy.
  • Bleeding, top down or bottom up, restores firm pedal feel.
  • Bleed whenever pedals feel spongy or the brake system has been opened.

SOURCES

  • FAA-H-8083-31B ch13 "Air in the Brake System"
  • FAA-H-8083-31B ch13 "Independent Master Cylinders"
Practice the Aviation Mechanic Airframe (AMA) test →Timed 100-question exam, by ACS area, or review your misses. Free.
MORE ON LANDING GEAR SYSTEMS

SkyDrill is not affiliated with the FAA. This is an original practice item based on FAA-H-8083-31B Aviation Maintenance Technician Handbook – Airframe, and 14 CFR part 43. Regulations and handbooks are revised; confirm details against the current edition.