You are preparing for a precision approach in a Boeing 777. According to the following information shown on the approach chart, which of the following is the correct choice of missed approach point?
OCH for A/B category aircraft: 400 ft
OCH for C/D category aircraft: 420 ft
(50 ft should be added for operational reasons)
Note: The wording here might be slightly different than in the exam, the feedback was unclear about it. Please let us know if you see the question and how it was phrased, thank you!
Short explanation:
- The Boeing 777 falls under the C/D category aircraft, with a reference height of 420 ft (plus an additional 50 ft for operational considerations).
- Precision approach: decision altitude or height (DA/DH):
- Category C/D aircraft: 420 ft (with 50 ft added for operational reasons). Therefore, the calculation simplifies to: DH = 420 ft + 50 ft = 470 ft
Detailed explanation:
So one part of this question is asking you to choose from MDH or DH.
Decision Height (DH) refers to precision approaches, and is the lowest height above the runway threshold where the pilot must begin a missed approach, if the runway is not yet in sight. So operationally, it is where you decide to continue if visual, or begin the go-around procedure if you are not yet visual.
Minimum Descent Height (MDH) refers to non-precision approaches (NPAs), and is a relic of the past, where NPAs could be flown by descending to the MDA/H and flying level until visual with the runway or the missed approach point.
- So therefore, as we are dealing with a precision approach here, the answer begins with DH.
The next job is to work out what the DH of the approach will be for that B777. It is a very large aircraft and accompanies approach categories C/D (two categories because its circling speed puts it in a different category to the VAT speed).
The approach category of an aircraft depends on its VAT speed (speed over the threshold) at MLM (maximum landing mass), or circling minima, which can give it two categories, as mentioned above. Having categories for this means that different approach speeds can be taken into account for obstacle clearance, circle to land and go-around manoeuvres.
As the B777 category is C/D, we can use 420 ft, plus the 50 ft addition (it is very common to add a small amount like this, for different corrections and safety margin, decided by the operator).
Therefore our answer is DH = 470 ft.
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