MOC

28.10.2004

Submission:

Was wondering what the readers thoughts are with regards to missed approach clearance surfaces. If you look at TERPS criteria the missed surface starts at MDA - MOC and any adjustments. If you have a TACAN approach you start your surface 250' below the MDA. If you have no penetrations to the surface you retain the 250' plus you are also gaining 48' of MOC since the aircraft is mandated to climb at 200 FPNM. If you look at Pans Ops (which I only understand a little) it appears you are provided 30 to 50 Mtrs instead of MDA/DA minus MOC.

On a departure you are only provided 48' MOC and if the surface is penetrated you publish a climb gradient above 200 FPNM to maintain the 48'. On a missed approach as long as an obstacle does not penetrate more that MOC you started with A/C 200 FPNM performance will still provide 48' per NM. Does not seem logical to publish a climb gradient table on an approach plate less than 200 FPNM.

I know departure and missed are different but was the intention to apply departure philosophy in missed approach? I like the idea of a level surface but if the intent is to only have 48' of clearance for each mile travelled why are we building in a buffer for missed which is not possible in a departure situation?


Dave Perry

Answer or Commentary:

(I.W.

Following are a few pictures to show the Pans-Ops-Ops case.

Basically in my opinion a departure and a missed approach are similar. The aircraft is starting at a position and going up but the two procedures use different criteria. I would be interested to hear from anyone that has any historical background as to why this is the case.)