时间：2011-04-18 00:52来源：蓝天飞行翻译 作者：航空 点击：次
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7.3.2 FIG 7.3.4 Vortex Flow Field Several Hundred Ft.,/Min. Several Hundred Ft.,/Min. FIG 7.3.5 Vortex Movement Near Ground . No Wind FIG 7.3.6 Vortex Movement Near Ground . with Cross Winds Wake Turbulence 7.3.3 5. There is a small segment of the aviation community that have become convinced that wake vortices may “bounce” up to twice their nominal steady state height. With a 200.foot span aircraft, the “bounce” height could reach approximately 200 feet AGL. This conviction is based on a single unsubstantiated report of an apparent coherent vortical flow that was seen in the volume scan of a research sensor. No one can say what conditions cause vortex bouncing, how high they bounce, at what angle they bounce, or how many times a vortex may bounce. On the other hand, no one can say for certain that vortices never “bounce.” Test data have shown that vortices can rise with the air mass in which they are embedded. Wind shear, particularly, can cause vortex flow field “tilting.” Also, ambient thermal lifting and orographic effects (rising terrain or tree lines) can cause a vortex flow field to rise. Notwithstanding the foregoing, pilots are reminded that they should be alert at all times for possible wake vortex encounters when conducting approach and landing operations. The pilot has the ultimate responsibility for ensuring appropriate separations and positioning of the aircraft in the terminal area to avoid the wake turbulence created by a preceding aircraft. b. A crosswind will decrease the lateral movement of the upwind vortex and increase the movement of the downwind vortex. Thus a light wind with a cross runway component of 1 to 5 knots could result in the upwind vortex remaining in the touchdown zone for a period of time and hasten the drift of the downwind vortex toward another runway. (See FIG 7.3.6.) Similarly, a tailwind condition can move the vortices of the preceding aircraft forward into the touchdown zone. THE LIGHT QUARTERING TAILWIND REQUIRES MAXIMUM CAUTION. Pilots should be alert to large aircraft upwind from their approach and takeoff flight paths. (See FIG 7.3.7.)FIG 7.3.7 Vortex Movement in Ground Effect . Tailwind Tail Wind Tail Wind Touchdown Point Touchdown Point x Wake Turbulence 7.3.4 7.3.5. Operations Problem Areas a.A wake encounter can be catastrophic. In 1972 at Fort Worth a DC.9 got too close to a DC.10 (two miles back), rolled, caught a wingtip, and cartwheeled coming to rest in an inverted position on the runway. All aboard were killed. Serious and even fatal GA accidents induced by wake vortices are not uncommon. However, a wake encounter is not necessarily hazardous. It can be one or more jolts with varying severity depending upon the direction of the encounter, weight of the generating aircraft, size of the encountering aircraft, distance from the generat-ing aircraft, and point of vortex encounter. The probability of induced roll increases when the encountering aircraft’s heading is generally aligned with the flight path of the generating aircraft. b.AVOID THE AREA BELOW AND BEHIND THE GENERATING AIRCRAFT, ESPECIALLY AT LOW ALTITUDE WHERE EVEN A MOMENTARY WAKE ENCOUNTER COULD BE HAZARDOUS. This is not easy to do. Some accidents have occurred even though the pilot of the trailing aircraft had carefully noted that the aircraft in front was at a considerably lower altitude. Unfortu-nately, this does not ensure that the flight path of the lead aircraft will be below that of the trailing aircraft. c.Pilots should be particularly alert in calm wind conditions and situations where the vortices could: 1. Remain in the touchdown area. 2.Drift from aircraft operating on a nearby runway. 3.Sink into the takeoff or landing path from a crossing runway. 4.Sink into the traffic pattern from other airport operations. 5.Sink into the flight path of VFR aircraft operating on the hemispheric altitude 500 feet below. d. Pilots of all aircraft should visualize the location of the vortex trail behind larger aircraft and use proper vortex avoidance procedures to achieve safe operation. It is equally important that pilots of larger aircraft plan or adjust their flight paths to minimize vortex exposure to other aircraft. 7.3.6. Vortex Avoidance Procedures a.Under certain conditions, airport traffic control-lers apply procedures for separating IFR aircraft. If a pilot accepts a clearance to visually follow a preceding aircraft, the pilot accepts responsibility for separation and wake turbulence avoidance. The controllers will also provide to VFR aircraft, with whom they are in communication and which in the tower’s opinion may be adversely affected by wake turbulence from a larger aircraft, the position, altitude and direction of flight of larger aircraft followed by the phrase “CAUTION . WAKE TURBULENCE.” After issuing the caution for wake turbulence, the airport traffic controllers generally do not provide additional information to the following aircraft unless the airport traffic controllers know the following aircraft is overtaking the preceding aircraft. WHETHER OR NOT A WARNING OR INFORMATION HAS BEEN GIVEN, HOWEVER, THE PILOT IS EXPECTED TO ADJUST AIR-CRAFT OPERATIONS AND FLIGHT PATH AS NECESSARY TO PRECLUDE SERIOUS WAKE ENCOUNTERS. When any doubt exists about maintaining safe separation distances between aircraft during approaches, pilots should ask the control tower for updates on separation distance and aircraft groundspeed. b.The following vortex avoidance procedures are recommended for the various situations: 1.Landing behind a larger aircraft. same runway. Stay at or above the larger aircraft’s final approach flight path-note its touchdown point-land beyond it. 2.Landing behind a larger aircraft. when parallel runway is closer than 2,500 feet. Consider possible drift to your runway. Stay at or above the larger aircraft’s final approach flight path. note its touchdown point. |
