Plan de Prevención de Riesgos:

1. AFWA Contrail Product Overview. The

technique shown on the JAAWIN page is referred to as the ―Appleman‖ method. Jet exhaust at some temperature with some amount of vapor pressure mixes with ambient air at some other temperature and vapor pressure. The technique mixes air from these two sources. It is assumed that the ―mixed‖ air will exist at intermediate ranges of temperature and moisture values between the jet exhaust and the atmosphere. It is sometimes the case that intermediate temperature and moisture combinations will condense, even if the original

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Figure 2-77. Example Contrails Chart. jet exhaust and the atmosphere are not

themselves saturated.

If contrails are expected, the JAAWIN contrails chart (Figure 2-77) depicts the lowest and highest altitudes in hundreds of feet. In this example, contrails are expected between 47,800 and 65,500 feet.

655 (red) 478 (blue)

If the top is green, look for another contrail layer above by using the link for ―Layer 2‖. There will be another pair of numbers on that image.

2. Definition of Bypass: The term ―Bypass‖ refers to how a turbine engine operates. During normal operation, the intake air is split into two parcels, which move through the engine at different speeds. One parcel is compressed and heated (and slowed in the process), then sent out of the exhaust nozzle.

This is the portion that turns the fan blades. The other parcel ―bypasses‖ both the compressor and the combustion chamber, so is not burned. This is the portion that increases momentum, since the fan speeds up this parcel. A high-bypass engine will have a large fraction of the intake air bypass the compressor and combustion chamber. Conversely, a low-bypass engine will have a small fraction of the intake air bypass the compressor and combustion chamber. According to AFRL sources, values between 0.0 and 4.0 are classified as ―low-bypass‖. JAAWIN gives contrail forecasts for no-bypass, low-bypass, and high-bypass engines.

• Aircraft and Their Probable Engine

Bypass Categories. Note: the term ‗bypass‘

refers to the engine. It is possible that the engine on a specific jet may not be typical of that model of aircraft. Table 2-12 describes the typical, unmodified engine in the column ―Engine Type‖.

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Table 2-12. Engine bypass categories.

Table 2-14. Engine bypass categories.

Aircraft Engine MFR Engine Engine Type

T-38 General Electric J85-GE-5 Turbojet (no bypass) U-2 General Electric F-118-101 Turbojet (no bypass) KC-135A Pratt & Whitney J57-P-59W No bypass

B-1B General Electric F-101-GE-102 Low-bypass Turbofan B-52H Pratt & Whitney TF33-P-3/103 Low-bypass Turbofan C-9A/C Pratt & Whitney JT8D-9 Low-bypass Turbofan

C-141A/B Pratt & Whitney TF33-P-7 Low-bypass Turbofan F-15/A/B/E Pratt & Whitney F-100-PW-220/229 Low-bypass Turbofan

F-15/C/D Pratt & Whitney F-100-PW-220/229 Low-bypass Turbofan C-21A Garrett TFE-731-2-2B Low-bypass Turbofan F-16/C/D Pratt & Whitney F100-PW-200/220/229 Low-bypass Turbofan C-17A Pratt & Whitney F117-PW-100 Low-bypass Turbofan F-16/C/D General Electric F110-GE-100/129 Low-bypass Turbofan KC-135E Pratt & Whitney TF-33-PW-102 Low-bypass Turbofan B-2 General Electric F-118-GE-100 Low-bypass Turbofan F-117A General Electric F404-F1D1 Low-bypass Turbofan E-3A Pratt & Whitney TF33-PW-100A Low-bypass Turbofan

C-5A/B General Electric TF39-GE-1C High-bypass Turbofan E-4B General Electric CF-6-50E2 High-bypass Turbofan KC-10A General Electric CF-6-50C2 High-bypass Turbofan KC-135R/T CFM International

(SNECMA/GE)

CFM-56 High-bypass Turbofan

A-10 General Electric TF34-GE-100 High-bypass Turbofan VC-25A General Electric CF6-80C2B1 High-bypass Turbofan

3. Manual Method for Forecasting

Probability of Contrail Formation. Critical

relationships between pressure, temperature and relative humidity used to forecast contrails are shown on a plotted Skew-T in Figure 2-78. Construct a scaled overlay of Figure 2-78 for your Skew-T and use it to find the temperature and relative humidity necessary for the formation of contrails in the wake of a jet aircraft flying at a particular pressure level. At a particular flight altitude, only the flight altitude temperatures and relative humidity values are required to make a ―yes‖ or ―no‖ forecast for contrails.

• If the flight altitude temperature is to the right of the 100 percent curve, forecast no contrails regardless of the relative humidity.

• If the flight altitude temperature is left of the zero percent curve, always forecast contrails no matter what the relative humidity.

• If the flight altitude temperature is between the 0 and 100 percent curves, both the relative humidity and the flight altitude temperature are needed to forecast contrails.

•• Contrails form only if the actual relative humidity is equal to or greater than the value indicated at that point on the graph (called the uncertain or possible area).

•• If the humidity along the route is unknown, assume a 40 percent relative humidity if there are no clouds and a 70 percent relative humidity if there are clouds.

Note: Dashed lines and brackets on Figure 2-78 indicate curves in the 100- to 40-mb region.

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Figure 2-78. Jet Contrail Curves on a Skew-T.

Critical relationships between pressure, temperature, and relative humidity used to forecast contrails are shown in the figure. Dashed lines and brackets indicate curves in the 100- to 40-mb region.

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Table 2-13. Probability of contrail formation.

Enter table with temperature at pressure level of interest and read up to get probability.

Table 2-15. Probability of contrail formation. Enter table with temperature at altitude of interest and read up to get probability.

The accuracy of contrail forecasts is degraded by uncertainties in measuring relative humidity at high altitudes. Use the empirical data in Table 2-13 to estimate contrail probabilities when accurate upper-air temperature and relative humidity data are not available.

Apply the flight altitude and temperature at flight time in Table 2-13 to get the contrail probability. For example, at a pressure level of 250 mb and a temperature of -52°C, there is a 50 percent probability of contrail formation.

F. Forecasting In-flight Visibility for Air-