Flying to minimums: MDA, VDP and CDFA

Two ways to fly a non-precision final segment, the visual descent point that connects the two, and computing a VDP from real chart numbers.

13 min read · Instrument approach systems

After this lesson you can

  • Contrast the traditional stepdown technique with a continuous descent final approach (CDFA), and explain why CDFA is safer.
  • Define the visual descent point (VDP) and explain what it does and does not authorize.
  • Compute a VDP using the 300-feet-per-NM rule from an MDA and a TDZE read off a real chart.
  • Describe what to do when no VDP is published, using the FAA's own descent-rate method.

A non-precision approach hands the pilot a single number, the MDA, and nothing that tells them exactly when to leave it for the runway. Reach the MDA too early relative to the runway and you level off and fly level for a mile or more, waiting on a runway that has not appeared yet, hoping it does before the missed approach point. Reach it too late, or descend to it too fast, and you have no time left to see anything before you have to go missed. The visual descent point exists to answer exactly this problem, and it connects to a bigger idea: flying the whole non-precision final segment as one continuous, stabilized descent, instead of a series of dives and levels.

This lesson works through both techniques, defines the VDP precisely, and computes one from the numbers on a real chart: RNAV (GPS) RWY 29 into Portland International Jetport (PWM), a chart that publishes its VDP directly.

The rest of this lesson

  1. 1.Two ways to fly the same final segment
  2. 2.Why continuous descent wins
  3. 3.The visual descent point: a point, not a permission
  4. 4.Computing a VDP: the 300-to-1 rule
  5. 5.Reading it on the chart: RNAV (GPS) RWY 29, Portland
  6. 6.When no VDP is published
  7. 7.Putting it together: a stabilized non-precision approach

These 7 sections, their figures, the checks along the way and the end-of-lesson quiz come with the IFR track. Paid once, yours for good.

See what the IFR track costsEvery module 1 is free to read, no account, no card.

Key terms

Try to recall each definition before turning the card.