MOCA only gives you minium obstacles clearance altitude at a very limited area, so not good for emergency use, as it is limited to a smaller area, I would say the opposite, MOCA if you are visual, as it will only give you a small area where you are assured MOCA, while MORA gives you a larger area. But you need to read the definitions properly.
I know there are are various ways of getting MORA, but both KSS and Jeppesen, are written in JAR OPS (IEM OPS 1.250)
So this for me means that they are official approved methods to make certain you will have the minimum obstacle clearance.
The obstacle clearance in MOCA and MORA are the same, however MORA defines a larger area with regards to this, and is more applicable to IFR flight.
MOCA mainly clears you for the route segment, I have read that airlines uses MORA and MEA to calculate obstacle clearance in flight, none that I have read about have used MOCA.
MOCA in my opinion is to limited, as it is only good for the actual route segment, however in case of drift down, you would need to leave the route, and you would have to use MORA!
Same in icing conditions, MORA would be a better bet than MOCA!
My advice, don't spend to much time analyzing this, I have a friend how did that, end of the day, conclusion was the same! MORA will give you a better chance to avoid in your vicinity, so from that logic, that's what you should use, never heard of MOCA being the number used for IFR.
Remember MOCA has to be met in the entire MORA area, either Grid or Route!
MSA for approach area, ref.point + 25 Nm (emergency safe altitude)
(but not secured radio reception)
MORA - emergency on/off airways, off route segments etc.
Last edited by truckflyer; 10th July 2012 at 09:24.