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Navigating Your Next Approach: Choosing Between Category A, B, or C MinimumsVisibility.

Incorrect minimums during instrument approaches could lead to navigational errors.

,   and  Administrator
3 min read
Optimal minima selection on your approach paths could be your undoing.
Optimal minima selection on your approach paths could be your undoing.

Fly Right, Stay Safe: Unsure about your approach minimums with your Category A aircraft?

Let's tackle aircraft certification and approach categories

Certain rules govern aircraft certification, as defined by FAR 97.3, and these regulations determine an aircraft's approach category. The exciting part is called the Approach Reference Speed (Vref). Simply put, it's the magic speed for a smoothly executed final approach. Generally, if Vref isn't specified, it's calculated as 1.3 x Vso, which is the aircraft's stall speed in landing configuration at maximum gross weight.

Now here's the interesting part. You might have a Category A aircraft, but achieving the Category A minimums isn't automatic.

According to AIM 5-4-7(b), when your flight speed exceeds the published approach category, you're bound to use the higher category's minimums. For instance, if your Category A airplane is cruising at 130 knots during a straight-in approach, you ought to use Category C minimums.

Here's a shout-out to our famed birds of the sky:

Example 1 (Cessna 172 Skyhawk, Category A): If you fly the final approach segment at 95 knots (indicated), you'll need to use Category B minimums.

Example 2 (Cirrus SR-22, Category A): If you race along at 125 knots (indicated), you'll need to employ Category C minimums.

Sometimes, minimums remain unaltered across categories like in ILS examples.

Minimums Changed? Adapt!

Remember those days when AIM suggested using straight-in minimums based on your aircraft's certified category? Well, that's ancient history! It's all about your indicated airspeed flown (circling and straight-in) these days.

This updated rule makes perfect sense since higher minimums provide a bigger safety cushion when you're gunning it.

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Enrichment Data:

Indicated airspeed directly influences the minimum approach requirements for instrument approach procedures, taking into account aircraft approach category (e.g., Category A, B, C, D, or E).

FAR Part 97.3 (Instrument Approach Procedures) formalizes approach categories based on approach reference speed (Vref), which is 1.3 times the aircraft's stall speed in landing configuration at maximum gross weight or a specified higher speed by the operator or type certificate holder. The categories are:

| Category | Indicated Airspeed (IAS) at Threshold ||----------|--------------------------------------|| A | < 91 knots || B | 91 to 120 knots || C | 121 to 140 knots || D | 141 to 165 knots || E | > 165 knots |

AIM 5-4-7(b) (Minimums for Straight-in Landing Procedures) requires pilots to use the minimums for the approach category corresponding to their actual approach speed at the threshold if it differs from their aircraft's certified category. For example, if your aircraft is usually a Cat A aircraft but you're flying an approach at a Cat C speed, you must use Cat C minimums[1].

Key Points:

  • Indicated Airspeed at Threshold Determines Category: If your indicated airspeed at the approach threshold falls within a higher category than your aircraft’s published category, you must use the higher category's minimums[1].
  • Safety and Compliance: By ensuring terrain and obstacle clearance minimums are appropriate for your actual speed and energy state, not just the aircraft’s design, this ensures enhanced safety levels[1].
  • Example: If you fly a Cirrus SR-22 (usually Cat A) but approach at 125 knots indicated, you should use Category C minimums[1].

Summary Table

| Aircraft Typical Cat. | Actual IAS at Threshold | Minimums to Use ||-----------------------|------------------------|-----------------|| A | 85 knots | A || A | 125 knots | C || B | 135 knots | C || B | 100 knots | B |

  1. The regulations in FAR 97.3 dictate the approach category of an aircraft, determining the Approach Reference Speed (Vref) which is crucial for a smooth final approach.
  2. If Vref isn't specified, it's calculated as 1.3 times the aircraft's stall speed in landing configuration at maximum gross weight.
  3. Achieving the Category A minimums isn't automatic even for Category A aircraft.
  4. According to AIM 5-4-7(b), if your flight speed exceeds the published approach category, you're required to use the higher category's minimums.
  5. For instance, if a Category A airplane like the Cessna 172 Skyhawk cruises at 130 knots during a straight-in approach, Category C minimums should be used.
  6. Minimum approach requirements for instrument approach procedures are influenced by the indicated airspeed, taking into account the aircraft's approach category.
  7. The updated rule focuses on your indicated airspeed flown (circling and straight-in) for determining minimum approach requirements.
  8. This change makes sense since higher minimums offer a bigger safety cushion when flying at higher speeds.
  9. Enhanced safety levels are ensured by using minimums based on your actual speed and energy state, not just the aircraft's design.

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