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Generally this will be used for emergency, to make the calculations of this easier.
I think from the JAR definitions, it is not the MOCA you should use for emergency, it should be the MORA. Specially grid MORA, you need to check what grid you are in, check the adjacent grids, and use the one that is highest!
You can also use route MORA, but this will give a much more narrow band to work with, as you just explained.
To be honest I think MORA is the one you normally would use for emergency, not MOCA.
i read a lot of avation forums and no one can give absolute answer for this....most of them gives referance from jar-faa but still i quess every pilot not using this altitude so much.MORA derived by jeppssen(it must be not offical so how can u use it?) but moca is a offical altitude pls correct me if im wrong.Finally can we say in msa use approach plate altitude in flight for an emergncy use moca for emergency on a airway segment or decent below icing conditions and use mora for vfr aircrafts?????????
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 Jul 2012 at 09:24.
Lets say you are flying to an uncontrolled airport, previous radar controller gives you a direct off airway routing, and says goodbye once you descend through FL150... What altitude are you going to descend to?
We dont have contact with ATC anyway as its a unicom airfield we are using inertial navigation, so dont need ground based navigation.
We are flying into an airport tonight where the MEA is 12,000 feet, the DME arc is 6,500 feet, distance to FAF from the Arc joining point is 19 nms, FAF altitude is 4800 feet. So allowing 19/3 = 6300 feet plus 4800 = 11,100 feet, our maximum altitude for joining the arc is 900 feet below the MEA. GRID MORA is 8,000 feet. We further compound this by routing direct to the ARC, so the initial arc distance of 9nm is reduced. So if we descend to 9000 feet (due direction of flight), we can join the arc 13 miles from the FAF and we have saved a massive 1 minute of flight time, not bad after 3000 nms
Also the MORA is Jeppesen derived, so they didn't account for navigation coverage, it doesn't mean that it doesn't exist. We are navigating to a high altitude VOR and not a terminal VOR, so the theoretical range is based on height above the transmitter. (1.23√Receiver Ht (in feet) + 1.23√Transmitter Ht (in feet))