7.30. Enroute Descents.

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7.30.1. Objective. Smoothly transition from the enroute structure to a (low) instrument approach.

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7.30.2. Description. Descent according to assigned routing and altitude restrictions issued by ATC. The more commonly used method to descend for an instrument approach.

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7.30.2.1. Airspeed - 200-250 KIAS.

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7.30.2.2. Power - As required (See Table 7.1.).

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7.30.2.3. Speed brake - As required.

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7.30.3. Procedure. Lower nose and set power to achieve desired airspeed and rate of descent. Plan descent to allow configuration before the FAF.

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7.30.4. Techniques.

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7.30.4.1. If given the option of a pilot discretion descent, a 5-degree descent is comfortable and controllable. To determine when to start down using a 5-degree descent, multiply the altitude to lose in thousands of feet by 2 and add 10 miles. For example, if the altitude to lose is 20,000 feet, start down approximately 50 NM from the destination (20 multiplied by 2 = 40 plus 10 = 50 NM). The extra 10 miles allows for an instrument approach into the destination.

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7.30.4.2. Given an altitude to be at within a specified range, determine the pitch attitude by one of two methods:

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7.30.4.2.1. 60-to-l rule:

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7.30.4.2.1.1. Pitch change = Altitude to lose (hundreds of feet) divided by NMs. For example, lose 5,000 feet in 10 NM; 50 divided by 10 = 5 degrees nose low.

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7.30.4.2.1.2. Every 1 degree of pitch equals descent (or climb) of 100 feet per NM.

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7.30.4.2.2. EADI technique (Figure 7.3.).

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7.30.4.2.2.1. The 10 degrees nose-low line on the EADI represents NM to descend.

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7.30.4.2.2.2. Lower the nose, based on this scale, to altitude to lose (in thousands). For example, lose 10,000 feet in 20 NM. Set scale with 20 at 10 degrees nose-low line. Descent of 10 (thousand feet) is one-half of 20; therefore, pitch required is 5 degrees nose low.

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7.30.4.3. Verify descent gradient by cross-checking VSI. Calculate descent rate from airspeed and pitch (descent gradient).

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7.30.4.3.1. VSI = Groundspeed (NM/minute) multiplied by pitch (descent gradient) multiplied by 100. For example, 4 NM/minute (240 GS) multiplied by 5 degrees descent gradient multiplied by 100 = 2,000 fpm on the VSI.

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7.30.4.3.2. Use caution when calculating VSI with IAS or TAS. Significant winds change desired VSI for selected descent gradient. Headwinds result in lower VSI and tailwinds in higher. For example, descent above calculated with 240 TAS; expected VSI is 2,000 fpm; to maintain 5-degree descent gradient with a 60-knot headwind (180 GS); VSI is 1,500 fpm. Likewise, with a 60-knot tailwind (300 KGS), VSI is 2,500 fpm.

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7.30.4.4. Use GPS and/or NAVAIDs to maintain SA.

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