Minimum Safe Altitude.

Discussion in 'Cleared for the Approach' started by John777, Dec 17, 2016.

  1. John777

    John777 Pre-takeoff checklist

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    What I am mostly confused with MSA is that it is useless most of time because OROCA is higher than MSA most of time! (assuming LOST COMM situation).

    MSA provides obstacle clearances but OROCA also does and by definition it is for emergency use.

    What is so emergency that the FAA has established this altitude on every chart?

    All I have been involved with MSA was when I did my training on LOST COMM.
     
  2. midlifeflyer

    midlifeflyer Final Approach

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    It is informational so that you know what altitude you need to get to right away in the immediate vicinity when you are low down and have an emergency.

    What emergency would require you to not be able to simply fly the charted courses? I bet you'll know it if you have it!
     
  3. tsts4

    tsts4 Line Up and Wait

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    Go back and re-read the definitions for OROCA and MSA. OROCA is not an emergency use altitude nor is it depicted on an approach plate. It's an enroute altitude used to provide off airway MEA-like obstacle clearance without any Nav reception criteria so those of us who are /G and fly direct not using airways have a way to figure out a safe minimum enroute altitude.
     
    Last edited: Dec 17, 2016
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  4. aterpster

    aterpster Pattern Altitude

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    In many countries, MSAs are operational altitudes, but not in the U.S. In fact, U.S. MSAs are not compliant with 91.177 in Designated Mountainous Areas (DMAs). And, with the advent of RNAV IAPs, they have become all but useless on FAA RNAV IAPs in mountainous areas, because they are not sectorized. Check F70 in Southern California for a good example of a useless MSA.
     
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  5. John777

    John777 Pre-takeoff checklist

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    So, what kind of emergencies do we use MSA including Lost comm?
     
  6. tsts4

    tsts4 Line Up and Wait

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    You've lost your Nav radio(s) too, you have some type of gps, but the destination doesn't have a GPS approach so you are rolling your own. IMO in this age of GPS approaches and for part 91 ops the MSA has lost a lot, if not all relevance.

    Note, this example may no longer be valid as I'm not sure if there's any airports left that have IAPs where at least one isn't a GPS.
     
    Last edited: Dec 18, 2016
  7. aterpster

    aterpster Pattern Altitude

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    None. They are a hold-over from a bygone era. The FAA almost did away with them a couple of years ago. Did you look at my example? Attached.
     

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  8. midlifeflyer

    midlifeflyer Final Approach

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    I don't even think of lost comm as an MSA emergency. The one I think of is a loss of situational awareness, whether induced by the pilot or the nav equipment. Basically, apart from "somewhere around here" you don't know where you are.
     
  9. Qotile

    Qotile Pre-Flight

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    If you are being vectored (e.g. for traffic before you establish on an approach) and lose comms, the MSA can provide a safety margin. You probably don't know the MVA the controller was using, you are no longer on a published route (have no MEA or published segment altitude to reference), and your expected and assigned altitudes are probably the MVA whose sector boundaries are unknown to you. You could climb to the MSA and head towards the IAF.

    Definitely a bit of a contrived example.
     
  10. Shawn

    Shawn En-Route

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    OROCA is the yellow lines on the freeway.
    MSA is the rumble strips.
     
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  11. aterpster

    aterpster Pattern Altitude

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    That wouldn't work very well at F70 (the chart I posted above).
     
  12. AKBill

    AKBill Cleared for Takeoff

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    So very true. Fly your C150 over the Rockies and you will figure it out...:)
     
  13. midlifeflyer

    midlifeflyer Final Approach

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    If you look at the F70 chart, Wally posted, you may get a lot more value out of the chart's plan view showing where the higher and lower terrain is located than an MSA telling you you need to climb about 8,000' immediately.
     
  14. MAKG1

    MAKG1 Touchdown! Greaser!

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    One obvious one is loss of GPS signal during an RNAV approach. BTDT. To make it worse, there is no radio contact to anyone aside from CTAF below 2000 at that airport. Fortunately, it was coastal, so I could climb over the ocean.

    Loss of electric power would lose all approaches plus some of the instrumentation.
     
  15. FastEddieB

    FastEddieB Final Approach

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    I thought the "S" in MSA stood for sector, defined by lines of longitude and latitude.

    Edited to add: right on the abbreviation:

    https://www.ivao.aero/training/documentation/books/SPP_APC_MSA.pdf

    But I was thinking of Maximum Terrain Elevation Figures shown on Sectionals.

    Edited further to add, now just called Maximum Elevation Figure, as shown here in hundreds of feet:

    [​IMG]

    I now recall they used to indicate there was no terrain higher than, in this case, 9,700'. But that changed at some point to include obstructions.
     
    Last edited: Dec 18, 2016
  16. RussR

    RussR Line Up and Wait

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    That website is the "International Virtual Aviation Organisation", so I'd hardly consider it an authoritative source. In addition, due to the spelling of "Organisation", it's likely focused on non-U.S. aviation, and ICAO terms are sometimes different.

    Better to go to the Pilot/Controller Glossary section of the AIM, where it uses the term Minimum Safe Altitude and even refers to Minimum Sector Altitude as an ICAO term, granted for the same thing.
     
  17. FastEddieB

    FastEddieB Final Approach

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    That was just the first site that came up on a Google search.

    I'll stipulate that the Law of Primacy sometimes gets me, where I can quickly parrot back definitions and abbreviations, only to realize they may have changed in the last 40 years!
     
  18. aterpster

    aterpster Pattern Altitude

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    Minimum Safe Altitude. (AIM 5-4-5)

    Sectors for ground-based IAPs, not for RNAV. Ground-based sectors are defined by magnetic bearings from the designated facility.