MSA Vs OROCA

J

John777

Pre-takeoff checklist
Joined
Apr 1, 2016
Messages
199
Display Name
Display name:
Louis
OROCA and MSA are similar in concept but only difference to point out is the distances from specific point where obstacle clearance is guaranteed.

MSA uses 25nm and OROCA published for a particular quadrant.

For example, let's say that you went missed on ILS under lost comm for whatever the reason, and plan on making another attempt on same approach.

Since we are within 25nm from the NAVAIDS(such as VOR, NDB etc...), would you really compare two altitudes and fly the highest ?

I do not want the real life tips, but the one that sounds legal!

Thanks.

John.
 
Why would you look at the OROCA when you plan on coming back for the same approach? Use the MSA.
 
Do you have reference or credible source that explains more about the MSA?
 
If your in the chart, msa. That's what it's there for.
 
Also, if you're in mountainous areas, add another 1,000 ft to the MSA if it makes you feel better.
 
OROCA is an enroute altitude -- it's found on enroute charts and provides you a way to determine a minimum safe altitude when flying off airway direct where you don't have an MEA to reference.

MSA is an emergency altitude found only on Approaches.

Let me ask you this-- when you are flying an approach what is on the plate: OROCA or MSA? When flying enroute what's on the Low IFR: MSA or OROCA?
 
MSA... But why not MEA if on published missed/approach segments?
 
Eh, unless you are in some bizarre emergency situation you should not be even looking at the MSA. Unless you are flying the published approach, you shouldn't be looking at the approach plate. OROCA (or MORA if you're a Jepp guy) on the other hand can be a conservative altitude for off-airways flying. This is because the minimum ifr altitude is 1000 (2000 in mountainous areas) feet over the highest obstacle four miles left or right of course. Note, you have to use the OROCA properly. Since it only gives you the elevation figure for that airspace between the lat/lon lines, if you are closer to the edge of the block than 4 miles, you need to also check the adjacent block(s).

The Minimum Sector Altitude is NOT even always the minimum legal IFR altitude. It only guarantees 1000' foot of clearance to the obstacles, which isn't legal in mountainous areas. Further, not everything on your IFR plate is within the MSA ring. The MSA is centered on a navaid, not the center of the plate. While most plates don't go out 25 miles, some do.
 
Check out this route. PIXEY V23 CZQ. OROCA 12100. MEA 2000. OROCA's are there to assist you in complying with FAR 91.177 (2) if you aren't sure exactly where you are. They are not a "hard" altitude. You don't have to be at them every time you are off of published routes. The Catch 22 is, if you aren't sure exactly where you are, then how do you know if you are within the Grid for an OROCA
 
You're flying the missed and coming back for a second try. Wouldn't there normally be charted minimum altitudes for each segment of the approach? If you have to go back into the enroute environment to fly to an IAF, then OROCA or MEA. Usually not an issue anyway except in a lost comms situation, since you'll normally be getting vectors and altitude assignments from ATC.

I couldn't ever see using the MSA for anything other than an abnormal or emergency situation. It's not an operational altitude, and is strictly for "emergency" use.
 
azure said:
You're flying the missed and coming back for a second try. Wouldn't there normally be charted minimum altitudes for each segment of the approach? If you have to go back into the enroute environment to fly to an IAF, then OROCA or MEA. Usually not an issue anyway except in a lost comms situation, since you'll normally be getting vectors and altitude assignments from ATC.

I couldn't ever see using the MSA for anything other than an abnormal or emergency situation. It's not an operational altitude, and is strictly for "emergency" use.
Click to expand...
And, with RNAV IAPs they are not even sectorized. Look at F70's MSA. Totally useless.
 

Attachments

  • F70.jpg
    F70.jpg
    358.2 KB · Views: 22
aterpster said:
And, with RNAV IAPs they are not even sectorized. Look at F70's MSA. Totally useless.
Click to expand...

Yeah. That one is absurd. Is there some rule that justifies it? Or is it just the opinion of whoever was on duty that day when the chart was built?
 
The OP is about to go back, fly to the IAF and try another IAP, all while IMC and not receiving an ATC clearance in doing so. If they feel that's an emergency, then they have every right to consider it an emergency and AIM 6-4-1B backs up the assumption. Lost commo also falls under both the emergency sections of the Instrument Flying Handbook and the 7110.65.

The MSA will comply as a MIA and is listed as such in Part 97. It's even an altitude that's listed in the FIH for lost commo after a GCA. As I said, if you are in mountains areas, just add 1,000 ft to it.
 
Last edited:
Velocity173 said:
The OP is about to go back, fly to the IAF and try another IAP, all while IMC and not receiving an ATC clearance in doing so. If they feel that's an emergency, then they have every right to consider it an emergency and AIM 6-4-1B backs up the assumption. Lost commo also falls under both the emergency sections of the Instrument Flying Handbook and the 7110.65.

The MSA will comply as a MIA and is listed as such in Part 97. It's even an altitude that's listed in the FIH for lost commo after a GCA. As I said, if you are in mountains areas, just add 2,000 ft to it.
Click to expand...
I think you mean add 1,000 feet to it.
 
luvflyin said:
Yeah. That one is absurd. Is there some rule that justifies it? Or is it just the opinion of whoever was on duty that day when the chart was built?
Click to expand...
Some people in the FAA wanted to do away with MSAs entirely. The compromise was to not sectorize them on RNAV IAPs.
 
The OP is about to go back, fly to the IAF and try another IAP, all while IMC and not receiving an ATC clearance in doing so.
Click to expand...
I'm missing where that was ever a stated part of this discussion. Normally missed approaches are not an emergency. You follow the missed procedure and hold until ATC clears you to do something different. I might indeed consider lost comms at the missed approach hold to be heading towards an emergency.
 
flyingron said:
I'm missing where that was ever a stated part of this discussion. Normally missed approaches are not an emergency. You follow the missed procedure and hold until ATC clears you to do something different. I might indeed consider lost comms at the missed approach hold to be heading towards an emergency.
Click to expand...

And I never said a MA is an emergency either. It's authorized with the approach clearance but in this case the OP is lost commo and going back to shoot another approach without ATC clearance. That could very well be considered an emergency in the PIC's mind and also the controller's. Especially if they have to moved aircraft out of the way to accommodate the OP. So, in an emergency situation, I see no problems in using the MSA in the terminal environment and adding 1000 ft if in mountainous.
 
Yeah, I missed where the OP explicitly said this was a lost comms situation. Still, in most cases the MSA will be irrelevant even then, unless there is no charted route back to the IAF and the MSA is lower than the OROCA, or you have some kind of equipment failure in addition to lost comms, in which case it's not your day, and chances are you wouldn't be able to re-shoot the ILS anyway.
 
No MSA circles on approaches with TAAs (RNAV or otherwise). Amusingly, we have an ILS at the next airport over which has an ILS Z, traditional IAF with hold-in-loo, and an ILS Y with a TAA. The ILS Z shows how USELESS the MSA circle is (even in the OP's state case). The MSA is a 25 mile radius form the BZM VOR. That gets you to neither the IAF or to any part of the (primary) missed approach procedure. Fortunately, the missed approach hold is the same as the hold-in-loo. If you go to the alternate missed procedure, you'll have to fly out of the MSA circle, but at least the VOR with the hold there has a published route back to the IAF. The MSA is also 2400' higher than any altitude on the procedure (Or the missed). This is due to terrain/obstacles to the west (the TAA in that direction is 4300 ).

Z: http://155.178.201.160/d-tpp/1702/05683ILDZ28.PDF
Y: http://155.178.201.160/d-tpp/1702/05683ILDY28.PDF
 
Since the OP never published an example approach, I take it he was assuming that the MSA would cover the IAF. Obviously if he had a MAP that takes him back to the IAF, he'll take that over an MSA or an OROCA for that matter.

The MSA is when you have an emergency and no clearance back to an IAF. The lost commo procedure in the DOD FIH is an example. Doing a GCA, with the absence of lost commo instructions, military pilots are required to use the last assigned / MSA to get back to an IAP.
 
Last edited:
flyingron said:
No MSA circles on approaches with TAAs (RNAV or otherwise). Amusingly, we have an ILS at the next airport over which has an ILS Z, traditional IAF with hold-in-loo, and an ILS Y with a TAA. The ILS Z shows how USELESS the MSA circle is (even in the OP's state case). The MSA is a 25 mile radius form the BZM VOR. That gets you to neither the IAF or to any part of the (primary) missed approach procedure. Fortunately, the missed approach hold is the same as the hold-in-loo. If you go to the alternate missed procedure, you'll have to fly out of the MSA circle, but at least the VOR with the hold there has a published route back to the IAF. The MSA is also 2400' higher than any altitude on the procedure (Or the missed). This is due to terrain/obstacles to the west (the TAA in that direction is 4300 ).

Z: http://155.178.201.160/d-tpp/1702/05683ILDZ28.PDF
Y: http://155.178.201.160/d-tpp/1702/05683ILDY28.PDF
Click to expand...
TAAs are a great safety and operational improvement for RNAV-equipped aircraft. Unfortunately, TAAs don't fit well at some mountainous areas. And, there is at least one Center that refuses to have them in their airspace (ZLA).
 
Velocity173 said:
The MSA is when you have an emergency and no clearance back to an IAF. The lost commo procedure in the DOD FIH is an example. Doing a GCA, with the absence of lost commo instructions, military pilots are required to use the last assigned / MSA to get back to an IAP.
Click to expand...

Funny, there's a piece of regulation that tells you what to do in lost comm and consulting MSAs isn't in it.
 
flyingron said:
Mimimum legal IFR altitude since "cleared, filed, and, expected" no longer apply.
Click to expand...
Assuming we're talking abut IFR conditions, I would think that "The minimum altitude...for IFR operations" would apply, per 91.185(c)(2)(ii).
 
Palmpilot said:
Assuming we're talking abut IFR conditions, I would think that "The minimum altitude...for IFR operations" would apply, per 91.185(c)(2)(ii).
Click to expand...

Yup. The one thing, the FAR's, that hasn't changed all that much over the years often has the answer.
 
Palmpilot said:
It doesn't tell you what to do about routing after flying a missed approach.
Click to expand...
91.185 ends with the commencement of a missed approach at the destination airport. It is strictly pilot's emergency authority at that point.
 
You must log in or register to reply here.
Back
Top