Joined: 11 Dec 2005
|Posted: Fri Feb 22, 2008 11:50 am Post subject: Wheel Brakes Application in 737-300
|The importance of establishing the desired reverse thrust level as soon as possible after touchdown cannot be overemphasized. This minimizes brake temperatures and tyre and brake ware and reduces stopping distance on very slippery runways. The use of minimum reverse thrust almost doubles the brake energy requirements and can result in brake temperatures much higher than normal.
The use of autobrakes is recommended as it is effective due to timely application upon touchdown and symmetrical braking. For manual braking, smoothly apply a constant brake pedal pressure for the desired braking. For short or slippery runways use full brake pedal pressure. Do not attempt to modulate, pump or improve the braking by any other special techniques. The antiskid system stops the airplane for all runway conditions in a shorter distance than is possible with either antiskid off or brake pedal modulation. The antiskid system adapts pilot applied brake pressure to runway conditions by sensing an impending skid condition and adjusting the brake pressure to each individual wheel for maximum braking effort. When brakes are applied on a slippery runway, several skid cycles occur before the antiskid system establishes the right amount of brake pressure for the most effective braking. If the pilot modulate the brake pedals, the antiskid system is forced to readjust the brake pressure to establish optimum braking. During this readjustment time, braking efficiency is lost.
When the antiskid is inoperative, the following techniques apply:
- Ensure that the nose wheels are on the ground and the speedbrakes are extended before applying the brakes
- Initiate wheel braking using very light pedal pressure and increase pressure as ground speed decreases
- Apply steady pressure and DO NOT PUMP the pedals
Flight testing has demonstrated that braking effectiveness on a wet grooved runway is similar to that of a dry runway. Caution however must be exercised when braking on any wet, ungrooved portions of the runway with antiskid inoperative to avoid blown tires.
The brake temperature monitor readings may vary between brakes during normal braking operations. Brake energy data provided in QRH should be used to identify potential overheat situations. To minimize brake temperature build-up:
- For airplanes without operative brake temperature monitoring systems: If the last ground time plus present flight time is less than 90 minutes, extend the landing gear 5 minutes early or 7 minutes prior to landing.
- For airplanes with operative brake temperature monitoring systems: Extend the landing gear approximately one minute early for each unit of brake temperature above normal.
Close adherence to recommended landing roll procedures ensures minimum brake temperature build up.