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MOCA, When To Use?  
User currently offlineTg 747-300 From Norway, joined Nov 1999, 1318 posts, RR: 0
Posted (8 years 4 months 4 weeks 1 day 23 hours ago) and read 9659 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)

tg 747-300


intentionally left blank
13 replies: All unread, jump to last
 
User currently offlineJspitfire From Canada, joined Feb 2005, 308 posts, RR: 2
Reply 1, posted (8 years 4 months 4 weeks 1 day 21 hours ago) and read 9648 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.

Jason


User currently offlinePilottim747 From United States of America, joined Jul 2001, 1607 posts, RR: 5
Reply 2, posted (8 years 4 months 4 weeks ago) and read 9588 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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User currently offlineHamad130 From Saudi Arabia, joined Nov 2005, 20 posts, RR: 0
Reply 3, posted (8 years 4 months 3 weeks 6 days 13 hours ago) and read 9555 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)

thank u all
HAMAD

( A GOOD PILOT IS ALWAYS LEARNING )



( A GOOD PILOT IS ALWAYS LEARNING )
User currently offlinespudsmac From United States of America, joined Feb 2008, 293 posts, RR: 0
Reply 4, posted (2 years 2 months 1 week 3 days 14 hours ago) and read 6483 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.

http://skyvector.com/?ll=33.85385688...11.33461408690313&chart=405&zoom=3

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.

[Edited 2012-02-09 11:41:37]

User currently offlinejetpilot From United States of America, joined May 1999, 3130 posts, RR: 29
Reply 5, posted (2 years 2 months 1 week 3 days 8 hours ago) and read 6405 times:

In case of comm failure you fly the MOCA, MEA or last assinged whichever is higher.

User currently offlineMir From United States of America, joined Jan 2004, 21103 posts, RR: 56
Reply 6, posted (2 years 2 months 1 week 3 days 5 hours ago) and read 6347 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



7 billion, one nation, imagination...it's a beautiful day
User currently offlineKELPkid From United States of America, joined Nov 2005, 6265 posts, RR: 3
Reply 7, posted (2 years 2 months 1 week 3 days 4 hours ago) and read 6341 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 :-)
User currently offlineMir From United States of America, joined Jan 2004, 21103 posts, RR: 56
Reply 8, posted (2 years 2 months 1 week 3 days 4 hours ago) and read 6332 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
User currently offlinejgarrido From Guam, joined Mar 2007, 339 posts, RR: 0
Reply 9, posted (2 years 2 months 1 week 3 days 3 hours ago) and read 6323 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.

User currently offlinen829th From United States of America, joined Mar 2009, 21 posts, RR: 0
Reply 10, posted (1 year 4 months 1 day 15 hours ago) and read 4004 times:

I'm looking to see if I'm able to fly MOCA to avoid Oxygen requirements. I'm flying a PA-34-200T from KIWA to U42 and do not have oxygen on board. The MEA on V257 in 14,500 for a large part on the leg, but the MOCA is 11,200. I can easily fly 12,000 and stay legal. That is if I'm able to fly that leg at or just above MOCA, but under MEA.

User currently offlineKELPkid From United States of America, joined Nov 2005, 6265 posts, RR: 3
Reply 11, posted (1 year 4 months 1 day 12 hours ago) and read 3952 times:

Quoting n829th (Reply 10):
I'm looking to see if I'm able to fly MOCA to avoid Oxygen requirements. I'm flying a PA-34-200T from KIWA to U42 and do not have oxygen on board. The MEA on V257 in 14,500 for a large part on the leg, but the MOCA is 11,200. I can easily fly 12,000 and stay legal. That is if I'm able to fly that leg at or just above MOCA, but under MEA.

I don't know if it would be legal to flight plan that. The FAA's computers will kick out the flight plan if you don't file for at least the MEA. If you do file a flight plan at that altitude, then you have to carry supplemental O2 on board   FBO's used to rent the bottles, but it's been a long time since I've seen one that did.



Celebrating the birth of KELPkidJR on August 5, 2009 :-)
User currently offlinewoodreau From United States of America, joined Sep 2001, 978 posts, RR: 6
Reply 12, posted (1 year 4 months 1 day 6 hours ago) and read 3894 times:

I use the MOCA when we've been cleared direct thru mountainous terrain and we're no longer on our filed routing (which is just about all the time)

So we're flying anywhere from FL360-410. Once we're cleared direct and not on flight plan routing all of the drift down decision points and planned enroute alternates from the dispatch release aren't valid anymore. So I use the MOCA as the lowest altitude I can go to if I need to do an emergency descent due to cabin depressurization. And I compare whether the MOCA is below my final driftdown cruise altitude to make sure I can stay above MOCA in the event of engine failure/OEI enroute.

That's just to give me a safe number until I can get a lower safe number from ATC or some other official number. I've never needed to use it in real life, but I keep it in the back of my mind as we're going direct over mountainous areas.



Bonus animus sit, ab experientia. Quod salvatum fuerit de malis usu venit judicium.
User currently offlineMir From United States of America, joined Jan 2004, 21103 posts, RR: 56
Reply 13, posted (1 year 4 months 22 hours ago) and read 3840 times:

Quoting n829th (Reply 10):
That is if I'm able to fly that leg at or just above MOCA, but under MEA.

Normally, you'd be fine doing that (assuming you weren't reliant on VOR navigation). There's nothing wrong with filing for above MOCA but below ME. Except that the problem in this case is that your route passes over the Grand Canyon SFRA, and you're not allowed to fly below 14,500' MSL on that airway in that area, thus the MEA - the MOCA listed is, in this case, for emergency purposes only.

You've got two alternatives. One would be either routing over V208 from GCN to PGA, then V293 to BCE and rejoining V257. The other would be to go from DRK via V562 to PGS, V235 to MMM, then V21 all the way to FFU (or DTA, depending on how you were planning on approaching U42). The first option is about 520nm, and the second option is about 510nm (in comparison to your original route of 470nm).

The third alternative would be to just go VFR and use the Dragon Corridor, which would allow you to cut across the canyon at 11,500 following fairly close to V257, then go direct to BCE to rejoin your airways. You'd get the benefit of seeing the canyon from above as well. However, I say this just from looking at the charts - I have no local knowledge of flying around the Grand Canyon, and I would seek out the opinion of someone who does before committing to that route.

-Mir



7 billion, one nation, imagination...it's a beautiful day
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