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Every 10 kt decrease in groundspeed on a 3° ILS glide path will require..
  • A
    an increase in the aircraft’s rate of descent of approximately 100 ft/min.
  • B
    a decrease in the aircraft’s rate of descent of approximately 100 ft/min.
  • C
    an increase in the aircraft’s rate of descent of approximately 50 ft/min.
  • D
    a decrease in the aircraft’s rate of descent of approximately 50 ft/min.

Rate of Descent is proportional to ground speed. Meaning that if the GS decreases, the ROD must also decrease in order to maintain the glideslope, and vice-versa (please refer to the formula below).

1:60 rule

ROD = (Glideslope in º x GS x 100) / 60
ROD = (3º x 10 kt x 100) / 60
ROD = 50 ft/mi

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