FAA Instrument Rating Airplane (IRA)IFR Procedures and ChartsHard
A pilot is flying a nonprecision approach to an airport without a published Visual Descent Point (VDP). The Final Approach Fix (FAF) is 5 NM from the runway threshold, and the MDA is 1,200 feet AGL. The pilot estimates a groundspeed of 120 knots. Approximately how far from the runway threshold should the pilot expect to begin a normal descent from the MDA, assuming a 3° glidepath?
- A2.5 NM
- B3.5 NM
- C3.0 NM
- D4.0 NM
Show answer & explanationAnswer & explanation
Correct answer: D. 4.0 NM
A common rule of thumb for a 3° glidepath is 300 feet per nautical mile. To descend from 1,200 feet AGL, the pilot would need 1,200 / 300 = 4 nautical miles. This is the approximate distance from the threshold where a normal descent from MDA should commence. This calculation helps determine a 'self-made' VDP.
Why the other options are wrong
- A. This distance would result in a steeper than 3° glidepath from MDA.
- B. This distance would result in a steeper than 3° glidepath from MDA.
- C. This distance would result in a steeper than 3° glidepath from MDA.
Estimated VDP Calculation
When no VDP is published, a pilot can estimate a descent point from MDA by using the '3:1 rule' (300 feet of altitude for every 1 nautical mile of distance) for a 3-degree glidepath.
- VDP is for nonprecision approaches.
- It marks the point from which a normal descent can be made.
- 3:1 rule: Altitude to lose (AGL) / 300 = distance in NM.
- Do not descend below MDA until visual with runway environment.
Memory trick: Three-to-one, the descent's begun, for a VDP that's none.