PPRuNe Forums - View Single Post - Jeppesen Approach Charts Non Precision DA
Old 3rd Mar 2011, 22:01
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FlightPathOBN
 
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Here is what that profile means with regards to the criteria...and what the chart means to the operator.

The Approach and Missed Approach are two completely separate designs. From the chart noted, Class A-D aircraft parameters apply, which means, basically the Class D performance was likely the worst case. (note that the criteria does not account for Engine Out)

On Approach, with the 3 degree GPA, a 200 foot ROC applies. Given the chart MDA, the obstacle is in the Missed Approach, or the MA parameters govern. (otherwise there would be an MDA 200 foot above threshold)

Now, the level section on the chart shown is an MDA. What isnt shown is the assumed parabolic curve that an aircraft takes when initiating a missed approach. This parabola is bounded by the level segment shown on the chart.
(note:if one initiates an MA, and the parabolic curve descends below the level segment altitude, one has failed)

Now, this parabola makes the following assumption, which is the same assumption that the crew must take into account when determining the real time DA, given this MDA.

The criteria assumes a 7 second timeframe, broken down as follows:
1. The pilot makes a decision to go missed, from the time the pilot makes that decision, it assumes 3 seconds to initiate the missed with the controls. (As a baseline, in roadway design, traffic lights are set to assume a 2 second decision time)
2. The aircraft takes 4 seconds to respond and begin the climb.

This is the foundation of the level section, a level surface that the aircraft must not penetrate.

For these procedures, the crew must take into account the current configuration, temps, loading, etc, and determine a real time climb gradient. This real time climb must fit within the bounds of the profile, and the crew must determine the real-time DA based on their situation.

This is certainly veiled in the chart, but is absolutely imperative for safe operations.

(In procedure engineering, I use the full 7 seconds, citing unknowns in crew experience, and calculate a DA based on several assumed climb gradients from 1.5% (criteria) to 12%, thus an engineered chart would show performance DA's that would not violate the MDA.)
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