Aircraft dimensions

25.10.2004

Submission:

Reference; ICAO State Letter SP22/4-00/84 dealing with recommendation 4/1 of the twelfth OCP meeting concerning the use of aircraft dimensions in the calculations of OCA/H.

The letter states "...concerning the need to take the geometry of the largest aircraft currently in operation into account when calculating obstacle clearance altitude/height for aircraft larger than the standard dimensions stated in" PANS-OPS VOL II Part III Chapter 21. "This recommendation arose from analyses carried out by several States on the effects of the largest current aircraft on the calculation of OCA/H. This had resulted in raising he OCA/H at a number of airfields and the publication of the relevant information in a special box on the instrument approach chart for aircraft with a semi-wing span greater than 30m. Although the present criteria in PANS-OPS, Vol II require States to account for aircraft dimensions larger than the standard assumption (semi-wing span = 30m), the appropriate PANS-OPS criteria have not been universally implemented."

I would appreciate hearing from those that have been applying these corrections [Ref; PANS-OPS Vol II Part III par 21.4.8.7.2 (and Attachment B)]:

(1) what the significance are? (Keeping in mind an A340 or 747-400 semi wing span comes to 32m)

(2) Do they also apply these corrections to smaller wing-span aircraft to obtain a lower OCA/H? Which would signify withdrawal of the aircraft dimension constant.

Gerhard Coetzee (Flight procedure specialist) South Africa