IAP minimums explination

[Guest]

Hi,Could someone explain the bottom of the IAP chart for me? I don't understand the DH section. I thought ILS cat's were I, II, IIIa,bor c but they have them as A, B, C, and D. Also when they write the minimums under the catagory the write somthing like 420/60 403 (400-1 1/4) that is the other bit I don't understand.Thanks

[KevinAu 441]

The word category when used with approaches has two meanings. One meaning refers to the class of approach and the other is the class of aircraft. A Cat II or III ILS will be found on a separately titled approach plate other than the normal Cat I. The Category A - D you find in the lower box on all approach plates refers to the minimums to be used for that approach depending on the stall speed of your aircraft or your maneuvering speed during a circle to land.The minimums in parenthesis is used only by the military.

[Guest]

Thanksso the letters in bold are for airliner use and the smaller ones are for millitary. What are the catagories of aircraft?Thanks againric

[woodreau 0]

The 420/60 403 (400-1 1/4) do mean something.the 420/60 is the 420ft / 6000ft 420ft meaning this is your decision altitude (DA) your altimeter when set to the right pressure will indicate 420ft (even though you will be 400ft about the ground (DH)) The field elevation is 20ft.6000ft meaning you need 6000ft visibility to legally land.403ft is the height you will be above the threshold when at DA.400ft is the DH 1 1/4 is the flight visibility in miles e.g. 6000ft = 1-1/4 statue milesThis is my initial explanation looking at this briefly and not looking at any pubs, I'll have to look it up again to tell you exactly or someone else can correct all my mistakes. You learn it once, but then you forget what this stuff really means after not looking at it for a long time.Cheers :)

[KevinAu 441]

The category speeds are A for 0-90, B for 91-120, C for 121-140, D for 141-165, and E for greater than 165 knots.

[woodreau 0]

Oops, never mind...after looking it up... I am wrong so....420/60 403 (400-1 1/4)depends on what kind of approach it is, but since you mentioned an ILS...420 DH - decision height60 RVR in hundreds of feet403 Height above thresholdnumbers in parenthesis are for military aircraft ... Iwas wrong here sorryif it is a LOC approach, should be right under the S-ILS block but only for cat I ILS's, Cat II and III ILS's have to have a working glideslope so no LOC420 - MDA60 - RVR403 HATCheers