How do you release DD3 safety actuator brakes?
- (a) Push in the yellow parking brake knob.
- (b) Press the brake pedal for 3–5 seconds.
- (c) Do both (a) and (b). ✓
- (d) Pump the brake pedal for 3–5 seconds.
Answer: C. (c) Do both (a) and (b).
Release DD3 safety actuator brakes by doing both: push in the yellow parking brake knob and press the brake pedal for three to five seconds.
Why this is the answer
The DD3 chamber locks the brake mechanically, and the handbook treats its release as a two-part action. You first operate the control valve that supplies air, then press the brake pedal for three to five seconds. The spring brake control valve section describes a yellow push/pull knob that is pushed to supply air and release the spring brakes, so pushing the knob is part of the release. The pedal step is still needed, which is why doing only one of the two actions is incomplete.
Why the other answers are wrong
- A. (a) Push in the yellow parking brake knob. — Pushing in the yellow knob starts the release by supplying air, but the DD3 procedure also requires pressing the brake pedal for three to five seconds.
- B. (b) Press the brake pedal for 3–5 seconds. — Pressing the brake pedal alone does not operate the control valve that supplies air to release the DD3 brake.
- D. (d) Pump the brake pedal for 3–5 seconds. — Pumping the brake pedal is not the DD3 release procedure; the handbook calls for operating the valve and then pressing the pedal for three to five seconds.
Remember it
For DD3 brakes, remember it takes both a knob and a pedal.