Low-Altitude Wind Shear and Its Hazard to Aviation (1983) / Chapter Skim
Currently Skimming:
3. Aircraft Performance and Operations
3. Aircraft Performance and Operations
Pages 51-78
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From page 51... ...
The Airman 's Information Manual (AIM) tells pilots when and how to report wind shears and other hazardous-weather information.
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From page 52... ...
gives the facility chief the option of using the centerfield wind information: "if operationally feasible, facility chiefs may elect to designate wind information derived from remote sensors located near runway thresholds as the wind to be issued to arriving aircraft rather than from the centerfield source, except that the centerfield source will be used during outages of the remote sensor/s." Such procedures as described above require the local facility chief to issue a letter to airmen explaining to arriving aircraft the origin of wind information, if it is obtained from a peripheral sensor. However, controllers are not required to specify the source of remote-wind data used when issuing these data to arriving aircraft, except when an alert occurs.
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From page 53... ...
CWSU meteorologists at the ATC center either now have or could acquire al 1 the information they need to prepare a transcribed broadcast of reported or predicted low-altitude wind shears and of any other hazardous weather occurring in or forecasted for the geographical boundaries of the center, including air carrier terminals and other airports. In the proposed system, meteorologists would upda te the taped advisory as required, which would be continuously broadcasted on a discrete frequency.
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From page 54... ...
In particular, the FAA should describe the structure of downbursts and enhance the discussion of airplane performance and piloting techniques in wind-shear conditions. Operating Procedures Airline flight operations manuals were reviewed by the committee as to the procedures specified for use by airline flight crews in the event of low-altitude wind-shear encounters.
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From page 55... ...
Airline flight operations manuals are organized differently from one company to another, as are their methods of presenting procedures for dealing with wind shears. Typically, all procedures related to takeoff and initial climb appear in one section of the manual and all procedures applicable to approach and landing appear in another.
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From page 56... ...
There are some potential problems with a pullup to stick shaker speed that should be considered: 0 If the pullup is accomplished too soon (significantly prior to imminent ground con-t-act) climb rate is actually decreased, since climb rate at stick-shaker speed is less than at V2, V2 + 10, or Vprog o If the pullup is accomplished too soon, and ground contact still occurs, there is no airspeed cushion to use for a "flare" to soften impact.
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From page 57... ...
All airlines appear to cover the subject extensively in ground training. As with operations manuals, the material is based largely on excerpts from the FAA's advisory circular, Boeing Airliner articles, and the technical literature.
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From page 58... ...
In view of the random and rare occurrences of wind shear in nature and because of the threat posed to flight safety by exposure to severe wind shears at low altitude, air carriers operating under Part 121 conduct such flight training in simulators. These devices are more economical to operate than airplanes and provide superior training capability for a range of abnormal and emergency training problems, including severe wind-shear encounters.
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From page 59... ...
Accurate portrayal of downbursts and wind-shear conditions and related aircraft responses in a simulator with motion base and visual displays presents a complex computer modeling problem. It requires extensive and expensive computation capabilities, available only in costly advanced simulators with large memory capacities, fast computation capabilities, and real-time cockpit controls and displays and response t imes necessary for the realis tic portrayal of wind-shear encount ers.
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From page 60... ...
Each of these wind components will produce a different response based on the airplane's aerodynamic configuration. A brief description of how an airplane responds to each of these wind shears along individual axes will contribute to an understanding of the wind-shear problem.
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From page 61... ...
Again, after several oscillations, the airplane wit 1 return to its original angle of attack and airspeed relative to the air mass, but it will be climbing relative to its original inertial flight path. The opposite situation, a downdraft, decreases an airplane's angle of attack, thus reducing lift and causing it to sink.
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From page 62... ...
However, while taking off or during go-around, precise heading control is not required, and some amount of dri ft from the runway centerline is acceptable. In summary, longitudinal and vertical wind shears can add energy to or subtract energy from an airplane.
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From page 63... ...
Simulator studies of flying a landing approach through severe wind shears of this type have shown that unles s an immediate go-around at a high pit ch angle and high thrust is initiated by the pilot, there could be little chance of s urvival . An increas ing headwind shear would appear to be benign since it carries the airplane above the glide slope and increases airspeed.
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From page 64... ...
General aviation aircraft that have lower stall speeds 64
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From page 65... ...
Some accidents have occurred in thunderstorms where the airplanes encountered heavy rain and wind shears simultaneously. Some preliminary analytical and experimental data indicate that heavy rain can degrade a wing's aerodynamic performance by reducing its maximum lift capability (Haines and Luers, 1982~.
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From page 66... ...
If a severe shear is encountered above this altitude, an airplane probably has enough altitude and speed margin to traverse the shear and have terrain clearance. As a downdraft approaches the ground, the ground presents a solid boundary that converts the vertical winds of the downdraft into an outflow of horizontal winds.
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From page 67... ...
Altitude Loss in Wind Shear on Landing Approach Analysis of the flight path of an airplane that penetrates a severe wind shear on landing is a complex problem. Figure 14 presents a generalized view of the altitude loss in transitioning from a 3° glide-slope approach to a go-around in tailwind shears of varying magnitude and intensity.
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From page 68... ...
Flaps and Gear Down , I 1 1 FIGURE 14 Transport Aircraft Flare Capability in Wind Shear from a Three-Degree Approach Path. v >~ go-around and flare performance for an aircraft with a system providing a warning of a shear encounter.
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From page 69... ...
Figure 14 considers only horizontal tailwind shears. The addition of downdrafts is difficult to present in a generalized form.
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From page 70... ...
While this appears to be a very favorable factor for light general aviation aircraft penetrating wind shears, it is by no means the only factor to be considered with regard to the hazards of severe wind-shear encounters. Also, the acceleration potential values presented in Table 4 are based on a static, instantaneous performance analysis and are only indicative of the relative acceleration capabilities of the aircraft types listed.
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From page 71... ...
2. Since the minimum operating speeds during takeoff and landing approach are defined as a percentage of the FAR stall speed, general aviation aircraft with low stall speeds will have smaller speed margins than do jet transports.
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From page 72... ...
As distinct from normal conditions, severe wind shears can drive an aircraf t to "the edge of the f light envelope" and beyond. Consequently, these aids mus t be optimal in the sense of generating maximum performance while maintaining safety marg in S .
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From page 73... ...
Systems can be assembled from off-the-shelf components; in fact, wind-shear warning devices are currently being sold, but only the most advanced fl ight directors contain some degree of wind-shear command capability to provide the required margin of safety and a minimum of schedule interruptions. More research and development must be done, particularly on ground and airborne "predictive" sensors.
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From page 74... ...
The automatic flight control systems on advanced transport aircraft have the capability to satisfactorily perform many of these functions automatically. Such systems and their associated displays constitute a near-term approach to providing adequate guidance and control aids for dealing with wind shear.
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From page 75... ...
~ _ . Perhaps encouraged by the degree of wind-shear penetration improvement reported by some of the studies discussed above, various avionics manufacturers have begun marketing products specifically designed to improve pilot performance in wind shears .
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From page 76... ...
Assuming that the aforementioned systems give correct command and display information to a pilot during all types of wind-shear encounters, they would be a useful addition to present transport and general aviation aircraft to reduce the hazard posed by wind shear s . However, the extent of their individual 76
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From page 77... ...
19110~. This notice discussed FAA research and development on wind shear, and it requested comments and recommendations to assist the agency in determining what, if any, regulatory proposals should be developed to amend FAR 121 to require wind-shear detection equipment or other onboard systems to assist in coping with hazardous wind shears.
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