Tg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0 Posted (6 years 6 months 5 days 6 hours ago) and read 4897 times:
Hi,
I have a little question regarding MOCA's vs MEA.
To my understanding: If for a given sector of an airway ( Victor and Colored) both a MEA and MOCA is provided, the MOCA will provide the required 1000 or 2000 obstacle clearance ( terrain dependent) and nav coverage within 22 nm of navaid,while the MEA will provide obstacle/terrain clearance as well as both com and nav coverage (with some exceptions)
I also understand that ATC can not assign you a MOCA if you're not within 22 nm of navaid.
So when is the MOCA actually used? In case of com failure? Or if your flying along an airway on your own (no atc)
Jspitfire From Canada, joined Feb 2005, 299 posts, RR: 2 Reply 1, posted (6 years 6 months 5 days 5 hours ago) and read 4883 times:
The way I understand it is ATC will clear you to the MOCA in an emergency. So for example if you need to get out of icing conditions or if you have an engine failure. I think they will also clear you to the MOCA if you are trying to get into an airport that doesn't have an instrument approach. They will let you go down for a few minutes and see if you can get into VMC conditions and proceed to your airport.
This is what I've learned in training, so someone correct me if I'm wrong.
Pilottim747 From United States of America, joined Jul 2001, 1607 posts, RR: 6 Reply 2, posted (6 years 6 months 3 days 8 hours ago) and read 4823 times:
When flying using RNAV (area navigation). You aren't using ground navigation aids like VORs and NDBs so you don't need navigation coverage but you need obstruction clearance.
pilottim747
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Hamad130 From Saudi Arabia, joined Nov 2005, 20 posts, RR: 0 Reply 3, posted (6 years 6 months 2 days 21 hours ago) and read 4790 times:
HI ALL
actually I Agree with my friend JASON . moca used at airfield without IAP because if u have IAP u can descend to minimum safe altitude or min sector alt
which is inside 25 NM from navaid .
By the way we have also MORA & GRADE MORA ( we use it in emergency or when we want to descend with radar coverage)
spudsmac From United States of America, joined Feb 2008, 262 posts, RR: 0 Reply 4, posted (3 months 2 weeks 1 day 22 hours ago) and read 1718 times:
I still have some questions about the MOCA after reading this. As I understand it, the MOCA guarantees obstacle clearance and also reception within 22 miles of the navaid. What about when the MOCA is more than 22 miles from the navaid. What then? I don't know what to tell my students and none of the other instructors seem to be able to give me a good answer.
There are plenty of examples in the link from skyvector. Take V528 for example, in a small piston aircraft, you would not normally be able to fly the published MEA of 16000, but if you were allowed to fly the MOCA, then you would be able to fly it. I feel like a rookie at the moment.
Mir From United States of America, joined Jan 2004, 17876 posts, RR: 59 Reply 6, posted (3 months 2 weeks 1 day 12 hours ago) and read 1582 times:
Quoting Tg 747-300 (Thread starter): I also understand that ATC can not assign you a MOCA if you're not within 22 nm of navaid.
ATC, as I understand it, doesn't really care about MOCAs except for in instances where they have no radar. Where there is radar coverage available, they have Minimum Vectoring Altitudes which are often lower than the MEA or MOCA, since they only have to account for localized obstacles, and radar coverage, not obstacles or navaid coverage along a full section of airway. If you're under radar coverage, ATC can assign you altitudes as low as their MVA. That said, if I were in mountainous terrain, I'd feel a bit iffy about accepting such a clearance if it were a ways below the MOCA.
Quoting spudsmac (Reply 4): What about when the MOCA is more than 22 miles from the navaid. What then? I don't know what to tell my students and none of the other instructors seem to be able to give me a good answer.
Then you're guaranteed terrain clearance but not navaid reception. This presents no problem when navigating by GPS (though there are such things as GPS MOCAs, which may be higher than the regular MOCAs - don't ask me about how that makes sense, because I haven't a clue), so you can file any altitude at or above the MOCA that observes the regular altitude rules for flight plans. However, there are a couple of things to consider:
1) If you happen to be using an RNAV system dependent on VORs for its position, I wouldn't trust the MOCA - fly at or above the MEA.
2) I wouldn't fly an airway whose MEA I could not climb to if needed, unless conditions were VMC along the way. If my GPS quits on me, I'm going to need to use the VORs again, and that means getting up to the MEA. By happy coincidence, the places where the MEAs are going to be highest are around mountainous terrain, where you really want to be able to get guaranteed navaid reception if you need it so that you don't fly into something hard and unforgiving. If it's VMC, then no problem - just climb as best you can, hope the navaids work properly, and see and avoid terrain.
Quoting jetpilot (Reply 5): In case of comm failure you fly the MOCA, MEA or last assinged whichever is higher.
Not quite correct. If you don't need the navigation coverage provided by the MEA (if you have GPS, for instance), you can fly at the MOCA if that is higher than any altitude you were assigned or have been told to expect - you don't have to go all the way up to the MEA.
-Mir
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KELPkid From United States of America, joined Nov 2005, 5610 posts, RR: 4 Reply 7, posted (3 months 2 weeks 1 day 12 hours ago) and read 1576 times:
MOCA is supposed to be for emergencies, but I've had to use it in real life when ATC rerouted my flight onto a different airway than I'd planned over the Cascades on a warm summer day, we just couldn't climb up to the MEA's on time. I advised ATC, and they were OK with it. We did get up to the MEA/ATC assigned altitude, just not before crossing the navaids/segment fixes
Celebrating the birth of KELPkidJR on August 5, 2009 :-)
Mir From United States of America, joined Jan 2004, 17876 posts, RR: 59 Reply 8, posted (3 months 2 weeks 1 day 12 hours ago) and read 1567 times:
Quoting KELPkid (Reply 7): MOCA is supposed to be for emergencies
I'm interested in where you heard this, because 91.177(a)(1) makes it seem like it's perfectly fine for you to operate down to the MOCA as part of normal operations, provided you have appropriate navigation signals.
-Mir
7 billion, one nation, imagination...it's a beautiful day
jgarrido From Guam, joined Mar 2007, 314 posts, RR: 0 Reply 9, posted (3 months 2 weeks 1 day 11 hours ago) and read 1558 times:
As a controller I've never had a need to know MOCA's. Now I haven't been doing this forever(10 years) and I haven't seen/done everything, but that's just my experience. For area's with radar I have MVA's and for those without radar I have MIA's. On occasion I've needed to know the MRA with a non-RNAV equipped aircraft and an airport where I wasn't able to vector to final, but that's about it.
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