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DA Altitude
CDGF
Topic Author
CDGF created the topic: DA Altitude
Hi
Appreciate some help on this.
With reference to DA altitude on ILS 3D are we allowed to -100 ft if actual QNH is available ?
for example if its a aerodrome that has a DA of 250FT & with shaded Gray box & PEC is not available what will be the DA.
1. case its has to be 250 + 50 = 300FT DA ?
2. case since the DA limit box is shaded - and actual QNH is available will the DA be 250FT - 100FT then add 50FT to Be 200FT ?
It is not uncommon for the LLZ MDA box to be shaded but it is not as common for the DA box to be shaded for an ILS approach. There are a few examples of this in the DAPs such as Amberley, Alice Springs, Avalon and Canberra. The unshaded boxes are usually for major airports with 24 hour tower operations. Your case 2 reasoning is correct. If the ILS DA box is shaded, you can subtract 100 feet from DA as long as you have set the actual QNH from an approved source. Also, if you did not apply PEC, you would have to add 50 feet to that reduced figure. Bit convoluted isn't it......
Hi bob
Many thanks for the help on this it is truely convoluted ! I actually came up with a similar question in the book with the melbroun/Essendon rwy26 ils which the da box is highlighted but published da was 590ft so was trying to grasp this hard.
Thank you so much for the help on this sir.
