If an ILS has a 3° glideslope and your groundspeed is 135 knots, what VSI reading should you maintain to stay on the glideslope?

If an ILS has a 3° glideslope and your groundspeed is 135 knots, what VSI reading should you maintain to stay on the glideslope?

• A. About 500 fpm
• B. About 675 fpm
• C. About 750 fpm
• D. About 900 fpm

Answer: (B)

To determine the vertical speed indicator (VSI) reading needed to maintain a 3° glideslope at a groundspeed of 135 knots, you can use the relationship between groundspeed, angle of descent, and vertical speed. Firstly, a 3° glideslope translates into a descent rate that can be calculated using the formula: 1. **Convert the groundspeed from knots to feet per minute (FPM)**: There are 6076 feet in a nautical mile and 60 minutes in an hour, so at 135 knots: \[ 135 \text{ knots} = 135 \times \frac{6076 \text{ feet}}{\text{nautical mile}} \times \frac{1 \text{ nautical mile}}{60 \text{ minutes}} \approx 13415 \text{ feet per minute} \] 2. **Calculate the descent rate using the glideslope**: For a 3° slope, the descent rate can be found through the formula: \[ \text{Descent Rate (FPM)} = \text{Groundspeed (knots)} \times 5 \] Plugging in the

To determine the vertical speed indicator (VSI) reading needed to maintain a 3° glideslope at a groundspeed of 135 knots, you can use the relationship between groundspeed, angle of descent, and vertical speed.

Firstly, a 3° glideslope translates into a descent rate that can be calculated using the formula:

1. Convert the groundspeed from knots to feet per minute (FPM): There are 6076 feet in a nautical mile and 60 minutes in an hour, so at 135 knots:

[

135 \text{ knots} = 135 \times \frac{6076 \text{ feet}}{\text{nautical mile}} \times \frac{1 \text{ nautical mile}}{60 \text{ minutes}} \approx 13415 \text{ feet per minute}

]

2. Calculate the descent rate using the glideslope: For a 3° slope, the descent rate can be found through the formula:

[

\text{Descent Rate (FPM)} = \text{Groundspeed (knots)} \times 5

]

Plugging in the