曝光台 注意防骗
网曝天猫店富美金盛家居专营店坑蒙拐骗欺诈消费者
If a landing is planned on a runway contaminated with snow, slush, standing water, or during heavy rain, the following factors must be considered: available runway length; visibility of runway markers and lights; snowbanks and drifts along the runway; wind direction and velocity; crosswind effect on directional control; braking action; possibility of effect on the airplane from slush and water spray (engine ingestion, damage to flaps, gear doors, etc.); and the probability of hydroplaning and its effect on stopping distances.
A common form of hydroplaning is dynamic hydroplaning. It occurs when there is standing water on the runway surface. Water with a depth of about one-tenth of an inch acts to lift the tire off the runway surface. This condition can progress to where the tires no longer contribute to directional control and braking action is nil.
The minimum dynamic hydroplaning speed of a tire has been determined to be
8.6 times the square root of the tire pressure in pounds per square inch. With a main wheel tire pressure of 180 psi, the calculated hydroplaning speed is approximately 115 knots. With a nosewheel tire pressure of 155 psi, the calculated hydroplaning speed of the nosewheel tire is approximately 107 knots. Nosewheel tire hydroplaning might be encountered while executing a high speed turnoff. The calculated hydroplaning speed referred to is for the start of dynamic hydroplaning. Once hydroplaning has started, it may persist to a significantly slower speed.
Braking action can become inhibited following the application of chemical de-icers on an icy runway. When first applied, the chemicals provide a watery film over snow and ice that results in an extremely low coefficient of friction. When in doubt about the type of runway de-icing, ask the tower specifically if chemical de-icers were used.
Blowing or drifting snow can create optical illusions or depth perception problems during landing or taxi-in. In crosswind conditions, they may create a false impression of airplane movement over the ground. It is possible to have an impression of no drift when in fact a considerable drift may exist. When landing under these conditions, runway markers or runway lights can help supply the necessary visual references.
When it has been established that a safe landing can be made, the airplane must be flown with the objective or minimizing the landing distance. The approach must be stabilized early. Precise control over drift and approach speeds is mandatory. Execute a missed approach if zero-drift condition cannot be established prior to touchdown. When making the transition to visual reference for landing, continue to utilize the glideslope and VASI information to control the glidepath as wet windshields and snow-covered surfaces may distort depth perception. The airplane should be flown firmly onto the runway at the aiming point. Avoid holding off. Be prepared to manually deploy the spoilers if automatic deployment does not occur as wheel spin-up may be delayed.
On touchdown, take positive action to lower the nose gear to the runway and maintain moderate forward pressure on the control column to assist in directional control. Avoid excessive forward control column pressure in order to retain maximum braking effectiveness and to reduce the possibility of nose wheel spray. Maintain centerline tracking, ensure spoiler deployment, and simultaneously apply brakes smoothly and symmetrically, as appropriate to the braking action and runway length available to ensure a safe stop. On contaminated surfaces, full braking should be used to realize optimum anti-skid operation. Autobrakes, if available, should be used in the maximum setting. The normal braking technique on slippery runways is that immediately after nose gear touchdown, apply brake pressure smoothly and symmetrically with maximum pedal pressure and hold until a safe stop is assured.
Apply reverse thrust to the idle reverse detent. After reverse thrust is verified, gradually increase reverse thrust as required up to a maximum of 1.3 EPR. If necessary, reverse thrust should be applied smoothly and symmetrically to maximum allowable as soon as possible since the reverse thrust effectiveness is greatest at higher speeds. If difficulty in maintaining directional control is experienced during reverse thrust operation, reduce thrust as required. Do not attempt to maintain directional control by using asymmetric reverse thrust as this will further aggravate the effects of weathervaning. Under emergency conditions, maximum reverse thrust may be used to a complete stop. The use of reverse thrust may cause a visibility problem from blowing snow forward as ground speed decreases and can melt dry snow which can impinge and freeze on cold surfaces. Take action appropriate to the braking effectiveness and runway length available. Avoid rapid return to forward thrust when engine RPM is high. The resultant forward thrust may be high enough to cause the airplane to accelerate.
Maintain directional control primarily with rudder pedals. Use differential braking as needed. Be alert for drift toward downwind side of the runway. The rudder required in strong crosswinds may cause the nose gear to turn to an angle which could induce skidding. Therefore, it may be necessary to hold the nose gear steering wheel centered while controlling steering with rudder and brakes to maintain tracking.
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：MD-80 Flight Manual 麦道80飞行手册 2(61)
